simdeck

„Disk je pun”, a mjesta ima"Disk full" with free space

Ponestalo inodea; obrisana datoteka koju proces drži otvorenomRunning out of inodes; a deleted file a process holds open

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• Pun disk na 28 %Disk full at 28%

Adresa, ruta i rezolverAddress, route and resolver

Tri stvari koje stroj treba za mrežu, i traženje ruteThe three things a host needs, and the route lookup

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• Ime vodi na krivu adresuA name leads to the wrong address
• Ime radi, ruta neThe name works, the route does not

cron i mjerači vremena: propušteni terminicron vs systemd timers: missed runs

Propušteni termini, Persistent= i nasumična odgodaMissed runs, Persistent= and randomized delay

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• Persistent=: tri propuštena termina, jedna nadoknadaPersistent=: three missed elapses, one catch-up
• Zamka ILI u cronu: dan u mjesecu i dan u tjednuThe cron OR trap: day of month and day of week

Datotečni sustavi s kopiranjem pri pisanjuCopy-on-write filesystems

Snimke dijele blokove; pisanje ide u nove blokoveSnapshots share blocks; writes go to new blocks

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• Sjenovite kopije i prethodne verzijeShadow copies and Previous Versions
• Puno diferencijalno područjeA full diff area
• Kopiranje ili preusmjeravanje pri pisanjuCopy-on-write vs redirect-on-write
• +1

Devet bitova dozvola, oktalni zapis i umaskNine permission bits, octal notation and umask

Devet bitova u tri zapisa; umask briše bitove: 666 uz 077 daje 600Nine bits written three ways; umask clears bits: 666 with 077 gives 600

istraživanjeexplorer

• Oktalni chmod briše nespomenuti bitOctal chmod erases a bit nobody named
• umask 077: 600, a ne 567umask 077: 600, not 567

Dozvole kažu da, SELinux kaže neDAC says yes, SELinux says no

Druga provjera nakon dozvola, po oznakama: tip, politika, način radaA second, label-based check after permissions: type, policy, mode

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• setenforce 0: prekidač, a ne popravaksetenforce 0: a switch, not a fix
• cp i mv s oznakom postupaju različitocp and mv treat the label differently

Gdje se gube podaci kontejneraWhere container data is lost

Sloj kontejnera, svezak ili vezano montiranje: što rm čuva, a što brišeContainer layer, volume or bind mount: what rm keeps and what it deletes

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Idempotentnost: skripta i playbookIdempotence: a script and a playbook

Skripta pokrenuta dvaput nešto pokvari; deklarativni zadatak neA script run twice breaks things; a declarative task doesn't

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• Tri zadatka, drugo pokretanjeThree tasks, the second run
• Rukovatelj samo nakon promjeneA handler only after a change

Imena, inodei i povezniceHard links, symlinks and inodes

Ime pokazuje na inode; brojač poveznica; viseća simbolička poveznicaNames point to inodes; the link count; dangling symlinks

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• Viseća simbolička poveznicaA dangling symbolic link
• rm, a prostor se ne vraćarm, and the space does not come back

Imenski prostori, veth i mostNamespaces, veth and a bridge

Kako se mreža kontejnera spaja ručnoHow container networking is wired by hand

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• Iz imenskog prostora u svijetFrom a namespace out to the world
• Zaboravljen ip_forwardForgot ip_forward
• Što sustav za kontejnere složi samWhat a container engine wires for you
• +1

Infrastruktura kao kod: konfiguracija, stanje i odmakInfrastructure as code: configuration, state and drift

Željeno, zapisano i stvarno: plan pokazuje razlikuDesired, recorded and real: plan shows the difference

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• Izgubljen zapis u stanjuA lost state entry
• Prihvaćanje odmakaAccepting drift

Izlazni status: &&, ||, set -e i pipefailExit status: &&, ||, set -e and pipefail

Kako se neuspjeh širi skriptom, i cjevovod koji javlja uspjeh iako je paoHow failure propagates, and a pipeline that reports success while failing

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• pipefail: cjevovod vraća 127pipefail: the pipeline returns 127
• Noćni posao javlja OK, a sigurnosna kopija je krnjaThe nightly job says OK, and the backup is truncated
• a && b || c nije if-elsea && b || c is not if-else
• +1

Kako regularni izraz pogađaHow a regex matches

Matcher hoda po retku, vraća se unatrag i provjerava sidraThe matcher walks the input, backtracks, anchors

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• a|ab: prvi pogodak ili najduljia|ab: first match or longest
• (a+)+b: stotine pokušaja(a+)+b: hundreds of tries

Kontejner bez root ovlasti: root unutra, običan vaniRootless containers: root inside, an ordinary user outside

Root u kontejneru preslikava se u neprivilegirani UID na domaćinuRoot inside the container maps to an unprivileged UID on the host

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• Kontejner bez root ovlasti: servisni korisnikRootless containers: a service user
• Kontejner bez root ovlasti: datoteka domaćina unutraRootless containers: a host file inside

Kontejner je procesA container is a process

Imenski prostori za PID, mrežu i montiranje izoliraju jedno stablo procesaPID, network and mount namespaces isolate one process tree

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• ps u kontejneru bez novog /procps in a container without a new /proc
• Kad PID 1 kontejnera umreWhen a container's PID 1 dies

Kontrolni zbrojevi i samoizlječenjeChecksums and self-healing

Provjera integriteta nađe loš blok i popravi ga iz zrcalaA scrub finds a bad block and repairs it from the mirror

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Kvote: meko i tvrdo ograničenje, razdoblje odgodeDisk quotas: soft and hard limit, grace period

Meko se smije prijeći dok traje razdoblje odgode; tvrdo zaustavlja pisanjeSoft limit: passable while the grace period runs; the hard limit stops the write

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• Kvote: kad razdoblje odgode istekneQuotas: when the grace period runs out
• Kvote vrijede po datotečnom sustavuQuotas hold per filesystem

Lanac podizanja sustavaThe boot chain

Firmware → pokretač sustava → jezgra → initramfs → systemd: lanac predajaFirmware → boot loader → kernel → initramfs → systemd: a chain of hand-overs

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• Krivi root=UUIDA wrong root=UUID
• Cilj nije dosegnutThe target is not reached
• Lanac podizanja WindowsaThe Windows boot chain
• Windows bez BCD-aWindows without its BCD
• +2

LVM snimka se puniAn LVM snapshot filling up

Područje kopiranja pri pisanju i nevaljana snimka kad se napuniCopy-on-write snapshot space, and invalidation when full

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Memorija, odlagalište i ubojica OOMMemory, swap and the OOM killer

Predmemorija se vraća, odlagalište daje mjesta, a OOM ubija najveći zbrojPage cache gives way, swap buys room, the OOM killer takes the top score

istraživanjeexplorer

• Slobodno 0, a stroj nije bez memorijeFree is 0, and the machine is not out of memory
• Ubojica OOM ubija bazuThe OOM killer kills the database
• Odlagalište spašava bazuSwap saves the database
• +1

Multipath: preuzimanje kad put padneMultipath I/O: path failover

Kad put do LUN-a padne, U/I se ponavlja na drugom putu ili čekaWhen a path to the LUN fails, I/O is resent on another path or waits

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Načini rada bondaBonding modes

active-backup, balance ili 802.3ad: što koji način rada žrtvujeactive-backup vs balance vs 802.3ad: what each gives up

istraživanjeexplorer

Navodnici i razdvajanje na poljaQuoting and word splitting

Što ljuska učini s retkom prije nego što ga naredba vidiWhat the shell does to a line before the command sees it

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• Uzorak u varijabli: rm $xA pattern in a variable: rm $x
• Zamjena naredbe: for f in $(ls)Command substitution: for f in $(ls)

NFS i root_squash: tko si, odlučuje poslužiteljNFS and root squash: the server decides who you are

Zahtjev nosi samo broj; poslužitelj ga preslikava, pa provjerava dozvoleA request carries only a number; the server maps it, then checks permissions

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• NFS: isti broj, drugi korisnikNFS: same number, another user
• root_squash ne štiti sveroot_squash does not cover everything

Obnova pod opterećenjem i drugi kvarRebuild under load and the second failure

Duga obnova, nečitljiv sektor, izgubljeno poljeA long rebuild, an unreadable sector, a lost array

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Od blokovnog uređaja do točke montiranjaBlock device to mount point

Disk → particija → datotečni sustav → montiranje; montiranje zaklanja sadržajDisk → partition → filesystem → mount; a mount hides what was there

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• Četiri sloja do stazeFour layers to a path
• Dva montiranja na istoj staziTwo mounts on one path

Ograničenja u cgroupscgroup limits

Težine i granica procesora, granice memorije; OOM unutar kontrolne grupeCPU weights and caps, memory limits; OOM inside a cgroup

istraživanjeexplorer

• Težina nije granicaA weight is not a limit
• memory.high usporava, ne ubijamemory.high slows down, it does not kill
• OOM unutar grupeOOM inside the group
• +1

Opterećenje sustavaLoad average

Opterećenje broji poslove u stanju R i D, a ne postotak procesoraLoad counts runnable and D-state tasks, not CPU percent

istraživanjeexplorer

• Dva posla na jednoj jezgriTwo tasks on one core
• Visoko opterećenje uz prazan procesorHigh load with an idle CPU

Ovisnosti i redoslijed jedinicaUnit dependencies and ordering

Wants/Requires povlače, After/Before određuju redoslijed; neuspjela ovisnostWants/Requires pull units in, After/Before set the order; a failed dependency

istraživanjeexplorer

• Requires= bez After=Requires= without After=
• After= ništa ne povlačiAfter= pulls nothing in

Ovisnosti paketa: sposobnosti, repozitoriji, sukobiPackage dependencies: capabilities, repositories, conflicts

Ovisnost traži sposobnost; pruža je paket iz bilo kojeg repozitorijaA dependency asks for a capability; a package from any repository provides it

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• Uklanjanje odnosi i nekorištene ovisnostiRemoving takes unused dependencies too
• Sukob paketaA package conflict

Paket kroz netfilterA packet through netfilter

prerouting, input, forward, output, postrouting: gdje su NAT i filtriranjeprerouting, input, forward, output, postrouting; where NAT and filter happen

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• Prosljeđivanje porta ide kroz forwardA port forward goes through forward
• accept nije konačanaccept is not final

PAM: kontrolne oznake odlučuju o prijaviPAM: control flags decide a login

required, requisite, sufficient i optional zajedno odlučuju o prijavirequired, requisite, sufficient and optional together decide a login

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• required pa sufficient: uspjeh se zanemarujerequired, then sufficient: the success is ignored
• pam_permit na vrhu: svatko ulazipam_permit on top: everyone gets in

Plavo-zeleno, kanarinac, postupno uvođenjeBlue-green, canary, rolling

Kako svaka strategija seli promet na novu inačicu i vraća lošu natragHow each strategy moves traffic to a new version and rolls a bad one back

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• Skrivena greška od 3 %A subtle 3 % bug
• Greška ispod pragaA bug below the threshold

Podljuske i hvatanje (trap)Subshells and traps

cd u podljusci ne ostaje; čišćenje na izlazu s trap … EXITA cd in a subshell doesn't stick; cleanup on EXIT

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• cd u podljusci ne ostajeA cd in a subshell doesn't stick
• exit u zagradama završava samo podljuskuexit in parentheses ends only the subshell
• Varijabla izgubljena u cjevovoduA variable lost in a pipeline
• +1

Posebni bitovi: setuid, setgid i stickySpecial bits: setuid, setgid and sticky

Proces dobiva efektivni UID vlasnika programa; u /tmp briše samo vlasnikA process gets the program owner’s effective UID; in /tmp only owners delete

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• Sticky bit: tko smije brisati u /tmpSticky bit: who may delete in /tmp
• setgid na direktoriju: grupa nove datotekesetgid on a directory: a new file’s group

Predmemorija stranica i prljave stranicePage cache and dirty pages

Predmemorija je posuđena, ne izgubljena; zapisano čeka na diskPage cache is lent, not lost; what you write waits for the disk

istraživanjeexplorer

• drop_caches: slobodno raste, raspoloživo nedrop_caches: free rises, available does not
• Gotovo pisanje nije na diskuA finished write is not on the disk

Proširenje logičkog volumena i datotečnog sustavaExtending an LV and its filesystem

Fizički volumen → grupa → logički volumen → datotečni sustav, tim redomPV → VG → LV → filesystem, in that order

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Put jedne poruke u dnevnikThe path of a log message

Program → journald → rsyslog → datoteka ili poslužiteljApp → journald → rsyslog → file or remote

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• authpriv.none i authpriv.*authpriv.none and authpriv.*
• Poslužitelj ne primaThe log server isn't receiving

Rotacija dnevnika: create i copytruncateLog rotation: create and copytruncate

Zapisivač piše u i-čvor: create traži reload, a copytruncate može izgubiti retkeThe logger writes to an inode: create needs a reload, copytruncate loses lines

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rsync: kosa crta na kraju i --deletersync: the trailing slash and --delete

src ili src/, i kako --delete zrcali pogreškusrc vs src/, and how --delete mirrors a mistake

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Seoba uživoLive migration

Pretkopiranje konvergira samo ako gost prlja sporije nego što veza kopiraPre-copy rounds converge only if dirtying is slower than copying

istraživanjeexplorer

• Gost prlja brže od vezeThe guest dirties faster than the link
• Prigušivanje gostaThrottling the guest

Signali: SIGTERM, SIGKILL, SIGHUP i nohupSignals: SIGTERM, SIGKILL, SIGHUP and nohup

Postupanje sa signalom odlučuje: zadana radnja, zanemari ili uhvatiThe disposition decides: default action, ignore, or catch

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Slojevi slike i kopiranje navišeImage layers and copy-up

Slojevi samo za čitanje, gornji za pisanje, kopiranje naviše, oznake brisanjaRead-only layers, a writable top, copy-up and whiteouts

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• RUN rm ne smanjuje slikuRUN rm does not shrink the image

Stablo direktorija u LinuxuThe Linux directory tree

FHS: što je gdje i zašto; gornja razina podijeljena je po ponašanju, ne po temiFHS: what lives where and why; the top level is split by behaviour, not topic

pregledreference

Stanja uzbune: na čekanju i aktivnaAlert states: pending and firing

Pravilo vidi samo uzorke; for traži uvjet bez prekida, pa treperenje ne okidaThe rule sees only scrapes; for wants an unbroken run, so flapping never fires

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• Treperenje uz for: 0Flapping with for: 0
• Skok između dva uzorkaA spike between two scrapes

Tablice particija: MBR i GPTPartition tables: MBR vs GPT

Ograničenja particija, zaštitni MBR i kopija zaglavlja na kraju diskaPartition limits, the protective MBR and the backup header

istraživanjeexplorer

• Disk od 4 TB s tablicom MBRA 4 TB disk with an MBR table
• Zaštitni MBRThe protective MBR

Tanki bazen i prekomjerno dodjeljivanjeThin provisioning and overcommit

Obećani i stvarni prostor: tanki bazen se puni pod svimaPromised vs real space: the thin pool fills under everyone

istraživanjeexplorer

• Jedan volumen puni bazenOne volume fills the pool
• Obrisano, a nije vraćeno bazenuDeleted, not returned to the pool

Tip 1 i tip 2, kontejneri i VM-oviType 1 vs type 2, containers vs VMs

Gdje sjede jezgra i hipervizorWhere the kernel and the hypervisor sit

pregledreference

Tko smije: vlasnik, grupa, ostaliWho may: owner, group, other

Vlasnik, grupa, ostali: odlučuje prva klasa koja odgovara; maska ACL-aOwner, group, other: the first class that matches decides; the ACL mask

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• Vlasnik bez prava, a svi ostali smijuAn owner with no rights, and everyone else may
• Unos kaže rwx, maska kaže rw-The entry says rwx, the mask says rw-

Tri toka, preusmjeravanje i cjevovodThree streams, redirection and pipes

stdin, stdout, stderr; poredak > i 2>&1; cijev nosi samo deskriptor 1stdin, stdout, stderr; the order of > and 2>&1; a pipe carries only fd 1

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• 2>&1 prije > : greška ostaje na zaslonu2>&1 before > : the error stays on the screen
• Greška kroz cijev: 2>&1 |The error through the pipe: 2>&1 |

Upravljanje poslovima: fg, bg, Ctrl-Z i odjavaJob control: fg, bg, Ctrl-Z and logging out

Posao je grupa procesa; tipke idu prednjoj grupi, SIGHUP svim poslovimaA job is a process group; keys go to the foreground group, SIGHUP to every job

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Usmjeravanje po praviluPolicy routing

ip rule bira tablicu prije traženja ruteip rule picks a table before the route lookup

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• Pravilo za izvor hvata i LANA source rule catches the LAN too
• Odgovor kroz krivu vanjsku vezuThe reply through the wrong uplink

Zone vatrozidaFirewall zones

zonu paketa određuje njegova izvorišna adresa ili sučeljea packet's zone comes from its source or its interface

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• Izvorišna adresa ispred sučeljaThe source address before the interface
• drop ili block: tišina ili odbijenicadrop or block: silence or a reject

Zrcalo nije sigurnosna kopijaA mirror is not a backup

RAID štiti od kvara diska, ne od brisanja ni pogrešnog sadržajaRAID protects against disk loss, not deletion or corruption

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Ceph grozd: CRUSH, PG-ovi, replikacija i oporavakCeph cluster: CRUSH, PGs, replication and recovery

Kako CRUSH smješta podatke i što grozd preživi kad mu dijelovi otkažuHow CRUSH places data, and what a cluster survives when parts of it fail

istraživanjeexplorer

• Hiperkonvergirana 3 čvora3-node hyperconverged
• 9 čvorova u 3 ormara9 nodes across 3 racks
• Tri replike, jedan ormarThree replicas, one rack
• Neuravnoteženi domaćiniUnbalanced hosts
• +2

Datotečno i blokovno spremišteFile vs block storage

NAS (NFS/SMB) ili SAN (iSCSI/FC): tko vodi datotečni sustavNAS (NFS/SMB) vs SAN (iSCSI/FC): who owns the filesystem

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Deduplikacija: odsječci stalne duljine i po sadržajuDeduplication: fixed vs content-defined chunks

Umetnut bajt pomiče sve fiksne odsječke; granice po sadržaju vraćaju se sameAn inserted byte shifts every fixed chunk; rolling-hash boundaries resynchronise

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Domena kvara u pravilu smještajaFailure domain in a placement rule

Isti podaci uz type host i uz type rack, pa se izgubi ormarSame data, rule by host vs by rack; then lose a rack

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down i out: kada Ceph kopiradown vs out: when Ceph copies

down: degradirano, ništa se ne miče; out nakon intervala: preraspodjeladown: degraded, nothing moves; out after a timer: rebalancing

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IOPS, propusnost i kašnjenjeIOPS, throughput and latency

Dubina reda i veličina bloka mijenjaju IOPS, propusnost i kašnjenjeQueue depth and block size trade IOPS, throughput and latency off

istraživanjeexplorer

• HDD: dublji red samo čekaHDD: a deeper queue only waits
• NVMe na stropu propusnostiNVMe at its bandwidth ceiling

Kodiranje s brisanjem ili kopijeErasure coding vs replication

Prostor, preživljeni kvarovi i cijena obnove: n kopija ili k+m dijelovaOverhead vs failures tolerated vs rebuild cost: n replicas or k+m shards

istraživanjeexplorer

• EC 4+2: cijelo, a ipak stojiEC 4+2: complete, yet stopped

Kopija koja lažeThe backup that lies

Kopija javlja uredno; tek proba oporavka pokaže što u njoj nemaBackups report OK; only a test restore shows what is missing

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• Tjedna kontrolna točka od 1,2 MBA 1.2 MB weekly checkpoint

Lanci slika diskaBacking chains

Čitanje pada kroz lanac, spajanje i prekinuta karikaReads fall through the chain, merging, and a broken link

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• Kontrolne točke u Hyper-V-uHyper-V checkpoints

LVM: topologijaLVM: topology

Kako fizički volumeni, grupa volumena i logički volumeni dijele ekstenteHow physical volumes, a volume group and logical volumes share extents

istraživanjeexplorer

Najmanji disk određuje kapacitetThe smallest disk caps the pool

Najpuniji OSD određuje MAX AVAIL; neravnomjerni poslužitelji pune se prviThe fullest OSD sets MAX AVAIL; uneven hosts fill first

istraživanjeexplorer

• Sjedište: „tek 38 % puno”HQ: "only 38 % full"

Odgođeno i izravno upisivanjeWrite-back vs write-through

Write-back je brz dok ne nestane struje; predmemorija s baterijomWrite-back is fast until the power fails; battery-backed cache

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Prebacivanje na pričuvnu lokacijuSite failover

DNS seli korisnike; sjednice i licencije vezane uz stroj ostaju izaDNS/GSLB moves users; sessions and machine-bound licences stay behind

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• Automatski DNSAuto failover
• Ručni DNSManual DNS
• Dugi TTLLong TTL
• Licencija ostajeLicence stays
• Povratak na AFail back
• +3

Prirasna i diferencijalna kopijaIncremental vs differential backup

Što koja kopija sprema i koje kopije treba oporavakWhat each backup stores, and what a restore needs

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• Slanje i primanje snimkiSnapshot send and receive

Prozor za kopiranje i prva izmještena kopijaBackup window and offsite seeding

Količina, propusnost i prozor: zašto prva kopija ide kamionomSize vs bandwidth vs window: why the first offsite copy goes by truck

istraživanjeexplorer

• Prva kopija kamionomFirst copy by truck

Retencija: djed-otac-sinRetention: grandfather-father-son

Koliko kopija raspored čuva i koliko se daleko unatrag može vratitiHow many copies a schedule keeps and how far back you can go

istraživanjeexplorer

• 7 dnevnih i 4 tjedne: koliko unatrag?7 daily and 4 weekly: how far back?
• Kad noćni posao padaWhen the nightly job fails

RPO i RTORPO and RTO

Koliko podataka i koliko vremena gubite, na jednoj vremenskoj crtiHow much data and how much time you lose, on one timeline

istraživanjeexplorer

• Noćna kopijaNightly backup
• Neuspjele kopijeFailing backups
• Tek u ponedjeljakFound on Monday
• Ucjenjivački softverRansomware
• Replika nije kopijaReplica is no backup
• +3

size i min_size: kada bazen stanesize and min_size: when a pool stops

size 2, min_size 2 staje na jednom kvaru; 3/2 ne stajesize 2, min_size 2 stops on one failure; 3/2 does not

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• Sjedište: pada osd.15HQ: osd.15 fails

Stratis: topologijaStratis: topology

Od lokalnog ili mrežnog blokovnog uređaja do bazena i tankog datotečnog sustavaFrom a local or network block device to a pool and a thin filesystem

istraživanjeexplorer

Unutrašnjost SSD-aInside an SSD

FTL, blokovi za brisanje, pojačanje pisanja, TRIM i trošenjeFTL, erase blocks, write amplification, TRIM and wear

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ZFS i Btrfs: topologijaZFS and Btrfs: topology

ZFS drži zalihost u vdevovima, Btrfs u profilima komada; što preživi otkaz diskaZFS puts redundancy in vdevs, Btrfs in chunk profiles; what survives a failure

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Datotečni sustavFile system

alokacija, slobodni prostor, inodeallocation, free space, inode

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Dodjela memorijeMemory allocation

particije, first/best/next-fit, buddypartitions, first/best/next-fit, buddy

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DretveThreads

ULT, KLT, kombinirani pristupULT, KLT, combined approach

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Karta operacijskog sustavaOperating system map

operacijski sustav u slojevimathe operating system in layers

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Međusobno isključivanje i sinkronizacijaMutual exclusion and synchronization

utrka, semafori, monitorirace conditions, semaphores, monitors

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Potpuni zastojDeadlock

graf resursa, bankarev algoritamresource graph, banker's algorithm

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PrekidiInterrupts

Ugniježđeni prekidi i stog jezgreNested interrupts and the kernel stack

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Prevođenje adresaAddress translation

straničenje, segmentacija, TLBpaging, segmentation, TLB

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ProcesiProcesses

Stanja procesa, PCB, fork/exec/waitProcess states, PCB, fork/exec/wait

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Put jednog pozivaJourney of a call

read() kroz cijeli sustavread() through the whole system

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RAID i priručna memorija diskaRAID and disk cache

RAID 0–6, paritet, disk cacheRAID 0–6, parity, disk cache

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Raspoređivanje diskaDisk scheduling

SSTF, SCAN, C-SCAN, FSCAN

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Raspoređivanje procesoraProcessor scheduling

FCFS, RR, SPN, SRT, HRRN, Feedback

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Sistemski poziviSystem calls

ulazak u jezgru, tablica poziva, povratakentering the kernel, the call table, the return

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Tehnike U/I i međuspremniciI/O techniques and buffering

programirani U/I, prekidi, DMAprogrammed I/O, interrupts, DMA

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Upravljački programiDevice drivers

slojevi U/I, gornja i donja polovicaI/O layers, top and bottom halves

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Zamjena stranicaPage replacement

OPT, LRU, FIFO, Clock

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Amdahlov zakonAmdahl's law

Ubrzanje ograničava dio programa koji se ne može ubrzatiSpeedup is limited by the part of a program that cannot be sped up

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Amdahlov zakon na web poslužiteljuAmdahl's law on a web server

Ubrzanje zahtjeva ograničavaju dijelovi koji nisu ubrzaniA request's speedup is limited by the parts that are not sped up

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Hazardi u protočnoj strukturiPipeline hazards

Podatkovni hazardi, zastoji, prosljeđivanje i poništavanje nakon grananjaData hazards, stalls, forwarding and the branch flush

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• Neovisne instrukcijeIndependent instructions
• Ovisnost bez prosljeđivanjaA dependency without forwarding
• Ovisnost s prosljeđivanjemA dependency with forwarding
• Load-use hazardThe load-use hazard
• Program s grananjemA program with a branch
• +3

Homogeni višejezgreni procesorHomogeneous multicore

Ubrzanje na više jezgri, koherencija predmemorija (MESI) i lažno dijeljenjeSpeedup on many cores, cache coherence (MESI) and false sharing

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Nuspojave sklopovlja: brzina, prostor, povjerenjeHardware side effects: speed, space and trust

Ispravni dijelovi ostavljaju tragove u dijeljenom stanju; optimizacija ih množiCorrect parts leave traces in shared state; optimising multiplies them

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Poredak okteta (endianness)Endianness

Poredak okteta u memoriji i na žiciByte order in memory and on the wire

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Preslikavanje u priručnu memorijuCache mapping

Izravno preslikavanje i skupna asocijativnost; promašaji zbog sukobaDirect mapped vs set associative; conflict misses

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• Ping-pong u jednom skupuPing-pong in one set
• Tri bloka u jednom skupuThree blocks in one set
• Susjedne riječiNeighbouring words
• 10 blokova u krug10 blocks in a loop
• +2

Rowhammer: smetnja među DRAM retcimaRowhammer: disturbance between DRAM rows

Česte aktivacije jednog retka prazne ćelije susjednih redaka prije osvježavanjaFrequent activations of one row drain the cells next to it before a refresh

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SRAM i DRAM ćelijaSRAM vs DRAM cell

SRAM drži bit u bistabilu; DRAM u naboju koji curi i treba osvježavanjeSRAM holds a bit in a latch; DRAM in charge that leaks and must be refreshed

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802.11: pridruživanje mreži korak po korak802.11 association step by step

Skeniranje, autentikacija, pridruživanje, pa rukovanje u četiri korakaScan, authenticate, associate, then the 4-way handshake

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Asimetričan put kroz NAT i vatrozidAsymmetric path through NAT and firewall

Odgovor vraćen drugim putem uređaj sa stanjem ne prepoznajeReplies taking another path break stateful devices

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Četiri vrste kašnjenjaFour kinds of delay

Kašnjenje prijenosa, širenja, obrade i čekanja u redu na jednom skokuTransmission, propagation, processing and queuing delay over one hop

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• Spora i brza vezaSlow and fast link
• Blizu i dalekoNear and far
• Preko satelitaVia a satellite
• Zauzet usmjernikBusy router
• Mali paketSmall packet
• +3

Cijeli put: od adrese do straniceThe whole journey: from URL to page

DNS, ARP, TCP, TLS i HTTP redom, kroz stvarni putDNS, ARP, TCP, TLS, HTTP in order, across the real path

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CRC i paritet: otkrivanje pogrešakaCRC and parity: error detection

CRC otkriva rafalne pogreške koje paritet promašiA CRC catches the burst errors that parity misses

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• Hammingov kod: ispravljanje pogreškeHamming code: correcting an error

Crtač mrežne topologijeNetwork topology drafter

Mrežna topologija otkrivana korak po korak: lokacije, zone i uloge uređajaA network topology revealed step by step: sites, zones and device roles

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• Dvije lokacije preko internetaTwo sites over the Internet
• Perimetar, DMZ i unutarnji LANPerimeter, DMZ and internal LAN
• Kampus: jezgra, distribucija, pristupCampus: core, distribution, access
• +1

CSMA/CA i RTS/CTSCSMA/CA and RTS/CTS

Wi-Fi izbjegava sudare koje ne može otkriti; RTS/CTS rješava skriveni čvorWi-Fi avoids collisions it can't detect; RTS/CTS fixes the hidden node

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CSMA/CD: kolizija i odustajanjeCSMA/CD: collisions and backoff

Kolizije na dijeljenom mediju i kako ih slučajno odustajanje razrješavaCollisions on a shared bus and how random backoff resolves them

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DHCP posrednik i giaddrDHCP relay and giaddr

Posrednik prosljeđuje broadcast kao unicast i označava podmrežuA relay forwards broadcasts as unicast and tags the subnet

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DHCP: DORA i zakup adreseDHCP DORA and the lease

Discover, offer, request, ack; obnavljanje na T1 i T2; istek dodjeleDiscover, offer, request, ack; renewal at T1 and T2; expiry

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Dijagnostika po slojevimaLayer-by-layer troubleshooting

Odozdo prema gore, odozgo prema dolje i podjela napola kroz isti OSI stogBottom-up, top-down and divide and conquer through the same OSI stack

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Dobro poznati portoviWell-known ports

Portovi koje studenti susreću, složeni po uslugama, i tri raspona IANA-eThe ports students meet, grouped by service, and IANA's three ranges

pregledreference

Enkapsulacija i dekapsulacijaEncapsulation and decapsulation

Svaki sloj dodaje svoje zaglavlje na putu dolje i skida ga na putu goreEach layer adds its header going down and strips it coming up

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Enkapsulacija na drugom i trećem slojuEncapsulation on layers 2 and 3

Svako zaglavlje uzima bajtove: okvir raste ili paket unutra mora biti manjiEvery header takes bytes: the frame grows, or the packet inside must shrink

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Fragmentacija i otkrivanje MTU-a putaFragmentation and path MTU discovery

Fragmenti ili DF i ICMP „potrebna fragmentacija”, te crna rupa PMTUD-aFragments vs DF and ICMP "fragmentation needed", and the PMTUD black hole

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Građa Ethernet okviraAnatomy of an Ethernet frame

Polja okvira, najmanja duljina od 64 okteta, nadopuna i FCSThe frame's fields, the 64-octet minimum, padding and the FCS

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IPv6 NDP umjesto ARP-aIPv6 NDP instead of ARP

Traženje susjeda ide na multicast adresu traženog čvora, ne svimaNeighbour solicitation goes to the solicited-node multicast, not to all

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• NDP: nitko ne odgovaraNDP: nobody answers
• NDP i hop limit 255NDP and hop limit 255

IPv6 SLAAC: samododjela adreseIPv6 SLAAC: address autoconfiguration

RS i RA, prefiks + identifikator sučelja, otkrivanje dvostruke adreseRS and RA, prefix + interface ID, duplicate address detection

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• EUI-64: identifikator iz MAC adreseEUI-64: the interface ID from a MAC
• Dvostruka IPv6 adresa (DAD)A duplicate IPv6 address (DAD)

Klizni prozor: veličina prozora i brzinaSliding window: window size and throughput

Brzina je prozor / kružno vrijeme, a nikad više od brzine vezeThroughput is window / round-trip time, never more than the link's rate

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Kolizijske i broadcast domeneCollision and broadcast domains

Koncentrator, preklopnik i usmjernik dijele različite domeneHubs, switches and routers split different domains

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• Primjer 3 iz knjigeExample 3 from the book
• Primjer 3 (b)Example 3 (b)
• Ured s koncentratoromOffice with a hub
• Bez usmjernikaNo router
• VLAN-ovi u mreži 1VLANs in network 1
• +3

Kontrola toka: prozor primateljaFlow control: the receiver's window

Primatelj prozorom kaže koliko prima; pošiljatelj ne smije preko desnog rubaThe receiver's window says how much it takes; the sender stops at its right edge

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Kontrola zagušenja u TCP-uTCP congestion control

Slow start, congestion avoidance i AIMD pila; Reno i CUBIC nakon gubitkaSlow start, congestion avoidance, the AIMD sawtooth; Reno and CUBIC after a loss

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Linijsko kodiranje: NRZ i ManchesterLine coding: NRZ vs Manchester

Kako bitovi postaju signal i zašto se takt mora moći izvući iz njegaHow bits become a signal and why the clock must be recoverable

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Lokalno ili udaljeno, pa ARPLocal or remote, then ARP

Računalo maskom bira odredište ili pristupnik i ARP-om traži njegovu MAC adresuThe host ANDs the mask, picks the target or the gateway, resolves its MAC

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Multicast i prisluškivanje IGMP-aMulticast and IGMP snooping

Članstvo u skupini; prisluškivanje IGMP-a drži tok dalje od drugih priključakaJoins, and IGMP snooping keeps the stream off other ports

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NAT: tablica prijevodaNAT: the translation table

Zapis nastaje kad paket krene van; dolazni paket bez zapisa se odbacujeAn entry is made when a packet goes out; inbound with no entry is dropped

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Nazivna propusnost i ostvarena brzinaNominal vs achieved throughput

Zaglavlja, polu-dupleks i ponovna slanja pojedu dio nazivne propusnostiOverhead, half duplex and retries eat the link rate

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• Oglašeno 100, izmjereno 82Advertised 100, measured 82
• 11 MB/s u pregledniku11 MB/s in the browser
• Najmanji okviriSmallest frames
• Gigabit, veliki okviriGigabit, large frames
• Koncentrator, tri staniceHub, three stations
• +3

Odlučuje prvi pogodakFirst match wins

Čita se odozgo, odlučuje prvo pravilo koje odgovara, na kraju skrivena zabranaRead top down, the first matching rule decides, an implicit deny ends the list

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Operatorski NAT: dva prijevodaCarrier-grade NAT: two translations

Dva NAT-a, dijeljeni prostor 100.64/10 i zašto prosljeđivanje porta ne pomažeTwo NATs, the shared space 100.64/10, and why port forwarding fails

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OSI i TCP/IP: koji sloj, koji uređajOSI vs TCP/IP: which layer, which device

Dva modela slojeva i sloj na kojem radi svaki protokol i uređajTwo layer models, and the layer each protocol and device works at

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Podmrežna maskaSubnet mask

Maska dijeli adresu na mrežni i host dio i odlučuje je li odredište blizuThe mask splits an address into network and host part and decides near or far

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Polja IPv4 zaglavljaIPv4 header fields

Čemu služi svako polje i koja se polja mijenjaju na putuWhat each field does and which fields change in transit

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Portovi i socketiPorts and sockets

pet vrijednosti razdvaja mnogo veza na jednom portu 443the 5-tuple keeps many connections apart on one port 443

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• Dvije kartice, isti poslužiteljTwo tabs, one server
• Isti par socketa je ista vezaThe same pair of sockets is one connection

Prelazak između access pointovaRoaming between access points

O prelasku odlučuje klijent, a ne AP; ljepljivi klijentiThe client, not the AP, decides when to roam; sticky clients

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Pristupni i trunk priključci, nativni VLANAccess and trunk ports, native VLAN

Gdje okvir dobiva 802.1Q oznaku, a gdje je gubi802.1Q tags added and removed at trunk edges

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Prosljeđivanje portovaPort forwarding

Dolazni spoj do poslužitelja iza NAT-a: stalan zapis mijenja odredišteInbound connections to a server behind NAT: a fixed row rewrites the destination

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• Objava porta kontejneraPublishing a container port

Razapinjuće stablo (STP)Spanning tree (STP)

Izbor korijenskog mosta, uloge priključaka i koji priključak blokira petljuRoot bridge election, port roles, and which port blocks the loop

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• Broadcast olujaBroadcast storm
• Bez petlje nema olujeNo loop, no storm
• Usmjernik kao granica broadcastaA router bounds the broadcast
• +1

Redovi za kvalitetu usluge (QoS)QoS queues

Strogi prioritet ili težinska podjela veze; pun red odbacuje pridošlicuStrict priority vs weighted fair queuing; a full queue drops the newcomer

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Sažimanje putevaRoute summarisation

Susjedni prefiksi u jednom zapisu, i što taj zapis pokriva viškaNeighbouring prefixes in one route, and what it over-covers

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Skraćivanje zapisa IPv6 adreseShortening IPv6 addresses

Vodeće nule van, najdulji niz nula-skupina postaje ::, i to samo jednomLeading zeros go, the longest run of zero groups becomes ::, and only once

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Skriveni čvor i RTS/CTSThe hidden node and RTS/CTS

Dvije stanice koje se ne čuju sudaraju se na access pointuTwo stations out of range of each other collide at the access point

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Stanje veze i Dijkstrin algoritamLink state and Dijkstra

Preplavljivanje LSA gradi jednu kartu, SPF bira puteveLSA flooding builds one map; SPF picks paths

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Statički i zadani putStatic and default routes

Zadani put hvata sve što ništa specifičnije ne hvata; petlju zaustavlja TTLThe default route catches what nothing more specific does; TTL ends a loop

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Što se mijenja na svakom skokuWhat changes at each hop

MAC adrese mijenjaju se po skoku, IP adrese ostaju, TTL pada, zbroj se računaMACs change per hop, IPs stay, TTL drops, the checksum is recomputed

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Što znače odgovori na pingWhat ping answers mean

Echo odgovor, kodovi nedostupnosti, istek TTL-a i što znači tišinaEcho reply, unreachable codes, time exceeded, and what silence means

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Tablica MAC adresaMAC address table

Preklopnik uči izvorišne adrese, a nepoznato odredište preplavljujeA switch learns source addresses and floods an unknown destination

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Tablica usmjeravanjaRouting table

Od svih zapisa koji se podudaraju, pobjeđuje najdulji prefiksOf all the entries that match, the longest prefix wins

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TCP i UDP pri gubitkuTCP vs UDP under loss

Isti niz: TCP šalje ponovno i zastaje, UDP gubi i nastavljaThe same stream: TCP retransmits and stalls, UDP drops and continues

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TCP SYN: otvoren, zatvoren, filtriranTCP SYN: open, closed, filtered

SYN dobije SYN+ACK, RST ili tišinu, i što koji odgovor dokazujeA SYN gets a SYN+ACK, an RST or nothing, and what each one proves

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• TCP SYN: tri ishoda u pravoj snimciTCP SYN: three outcomes in a real capture
• Vatrozid: odbaciti ili odbitiFirewall: drop or reject

TCP: gubitak i ponovni prijenosTCP: loss and retransmission

RTO, duple potvrde, brzi ponovni prijenosRTO, duplicate ACKs, fast retransmit

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• TCP: brzi ponovni prijenosTCP: fast retransmit

TCP: stanja vezeTCP: connection states

Stanja kroz koja socket prolazi, uživo: svaka strana ima svojeThe states a socket passes through, live: each end has its own

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TCP: trostruko rukovanjeTCP: the three-way handshake

SYN, SYN+ACK, ACK: potvrda je redni broj + 1, jer SYN zauzima jedan brojSYN, SYN+ACK, ACK: the ack is seq + 1, because the SYN takes one number

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• TCP: zatvaranje vezeTCP: closing a connection
• TCP: poslužitelj prvi zatvara vezuTCP: the server closes first
• TCP: poluzatvorena vezaTCP: a half-closed connection
• TCP: FIN i ACK u jednom segmentuTCP: FIN and ACK in one segment
• TCP: istodobno zatvaranjeTCP: simultaneous close
• +3

Traceroute i TTLTraceroute and TTL

Poruke o isteku TTL-a crtaju put, a zvjezdice nisu kvarTTL-exceeded replies map the path, and stars are not failures

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Udruživanje veza i raspodjela tokovaLink aggregation and flow hashing

Zašto jedan tok nikad ne premaši brzinu jedne članske vezeWhy one flow never exceeds one member link

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Usmjeravanje između VLAN-ovaInter-VLAN routing

Usmjernik na štapu ili sučelja VLAN-ova L3 preklopnikaRouter on a stick vs L3 switch VLAN interfaces (SVIs)

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Vatrozid bez stanja i sa stanjemStateless and stateful firewall

Odgovor treba zasebno pravilo, osim ako vatrozid pamti vezuThe reply needs its own rule, unless the firewall remembers the connection

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Vektor udaljenosti i brojanje do beskonačnostiDistance vector and count to infinity

Usmjernici razmjenjuju tablice, loša vijest putuje sporo, podijeljeni horizontRouters swap tables, bad news travels slowly, split horizon helps

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VLAN

Pristupni priključak nosi jedan VLAN, trunk označava okvire i nosi sveAn access port carries one VLAN; a trunk tags frames and carries them all

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VLSM: podmreže različite veličineVLSM: subnets of different sizes

Jedan prostor, blokovi po mjeri: najveći prvo, svaki poravnat na svoju veličinuOne space, blocks cut to size: largest first, each aligned to its own size

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Vrste IPv6 adresa i njihov dometIPv6 address types and their reach

Link-local, GUA, ULA i multicast: prefiks određuje vrstu, vrsta dometLink-local, GUA, ULA and multicast: the prefix sets the type, the type the reach

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Wi-Fi kanali i preklapanjeWi-Fi channels and overlap

2,4 GHz 1/6/11, širine kanala na 5 GHz, smetnje na istom kanalu2.4 GHz 1/6/11, 5 GHz channel widths, co-channel interference

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WPA2 i WPA3: rukovanje i što vidi promatračWPA2 and WPA3: the handshake and what an observer sees

Porijeklo PMK-a, rukovanje u četiri koraka; WPA2-PSK se pogađa bez mreže, SAE nePMK origin, 4-way handshake, why WPA2-PSK can be cracked offline and SAE can't

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Zaglavlja protokolaProtocol headers

Ethernet, IPv4, IPv6, TCP i UDP zaglavlja jedno uz drugo, u istom mjeriluEthernet, IPv4, IPv6, TCP and UDP headers side by side, to one scale

pregledreference

3-2-1 i nepromjenjive kopije protiv ucjenjivačkog programa3-2-1 and immutable copies vs ransomware

Koje kopije prežive šifriranje i brisanjeWhich copies survive encryption and deletion

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• 3-2-1 u mreži3-2-1 online
• Nepromjenjiva kopijaImmutable copy
• Vrpca izvan mrežeOffline tape
• +1

AAA i 802.1X: prijava na priključak mrežeAAA and 802.1X: logging in on a network port

Klijent, autentikator i RADIUS poslužitelj; priključak se otvara tek nakon EAP-aSupplicant, authenticator, RADIUS server; the port opens only after EAP

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Bočno kretanje i slojevi ovlastiLateral movement and tiering

Jedna administratorska prijava na radnoj stanici otvara cijelu domenuOne admin logon on a workstation exposes the whole domain

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• Samo LAPSLAPS only
• SlojeviTiering
• Skok po skokHop by hop
• +1

Diffie–Hellman

Zajednička tajna preko javnog kanala: prvo miješanje boja, zatim brojeviA shared secret over a public channel: colour mixing, then numbers

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Digitalni potpisDigital signatures

Potpis privatnim ključem, provjera javnim: svaka izmjena ga kvariSign with the private key, verify with the public key; tampering breaks it

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DMZ: matrica pravila vatrozidaDMZ: the firewall's rule matrix

Koja zona smije otvoriti što prema kojojWhich zone may open what to which

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Funkcije sažimanjaHash functions

Stalna duljina, lavinski učinak, cjelovitost i kolizije sažetkaFixed length, the avalanche effect, integrity and collisions of a hash

istraživanjeexplorer

• Jedan znak, pola sažetkaOne character, half the digest
• Kolizija malog sažetkaA collision in a toy hash

IPsec i IKE: tunel između dviju lokacijaIPsec and IKE: a site-to-site tunnel

Dvije razmjene IKE-a, tunelski i transportni način, ESPIKE's two exchanges, tunnel vs transport mode, ESP

korak po korakstep by step · 8 koraka8 steps

Preljev međuspremnika na stoguStack buffer overflow

Prepisivanje povratne adrese; kanarinac, NX i ASLROverwriting the return address; canaries, NX, ASLR

korak po korakstep by step · 5 koraka5 steps

Simetrično i asimetrično šifriranjeSymmetric vs asymmetric encryption

Problem raspodjele ključa i kako ga javni ključevi rješavajuThe key distribution problem and how public keys solve it

korak po korakstep by step · 11 koraka11 steps

Skriptiranje među stranicama (XSS)Cross-site scripting (XSS)

Pohranjeni i reflektirani XSS; kodiranje izlazaStored vs reflected XSS; output encoding

korak po korakstep by step · 7 koraka7 steps

Spremanje lozinkiStoring passwords

Lozinka, sažetak, sol i spori sažetak: što napadač dobije i koliko pogađaPlain, hashed, salted, slow-hashed: what an attacker gets and how long it takes

istraživanjeexplorer

• Ista lozinka bez soliOne password, no salt
• Lozinka od 4 mala slovaA four-letter password

Umetanje SQL-aSQL injection

Unos zalijepljen u upit postaje kod; parametri to sprječavajuConcatenated input becomes code; parameters fix it

istraživanjeexplorer

• ' OR '1'='1: uvijek istinito' OR '1'='1: always true
• Parametrizirani upitParameterized query

WireGuard: rukovanje, AllowedIPs i roamingWireGuard: handshake, AllowedIPs and roaming

Rukovanje u jednom povratnom putu, usmjeravanje po ključu, adresa naučena u hoduA 1-RTT handshake, cryptokey routing, and an endpoint learned on the move

korak po korakstep by step · 4 koraka4 steps

CAP pri razdvajanju mrežeCAP under partition

Razdvojen sustav bira: dosljednost ili dostupnostA partitioned system picks consistency or availability

korak po korakstep by step · 3 koraka3 steps

Domene kvara i minimalni rezni skupoviFault domains and minimal cut sets

Što je najmanje što obara uslugu, i zašto odgovor nikad nije »ništa«The smallest thing that takes a service down, and why it is never nothing

istraživanjeexplorer

• Tri zone, a opet nije nulaThree zones, and still not zero
• Tri ormara, jedna razdjelnica napajanjaThree racks, one power strip
• size=2, min_size=2
• Više regija, upravljačka ravnina u jednojMulti-region, single-region control plane
• Konfiguracijska izmjena stiže u svaku regijuA config push reaches every region
• +3

Dosljedno raspršivanjeConsistent hashing

Novi čvor na prstenu premješta 1/n ključeva, a mod n gotovo sveAdding a node moves 1/n of the keys on a ring; mod n moves almost all

istraživanjeexplorer

• Jedna točka po čvoruOne point per node

Kantica sa žetonima i kantica koja curiToken bucket vs leaky bucket

Nalet propušten odjednom ili razvučen u čekanjeA burst let through at once, or spread out as delay

korak po korakstep by step · 6 koraka6 steps

Kašnjenje autoskaliranjaAutoscaling lag

Vrijeme isporuke kapaciteta prema vršku opterećenja; prekid spot instanceCapacity lead time against a load spike; spot preemption

istraživanjeexplorer

• Rezervirani blokReserved block
• Brzo autoskaliranjeFast scaler
• Sporo autoskaliranjeSlow scaler
• PrekasnoToo late
• Spot i domene kvaraSpot and failure domains
• +3

Kašnjenje pri gotovo punoj iskorištenostiLatency near full utilisation

Vrijeme čekanja eksplodira kad iskorištenost ρ ide prema 1Waiting time explodes as utilisation ρ goes to 1

istraživanjeexplorer

• Pola opterećenjaHalf load
• KoljenoThe knee
• Skoro punoNear full
• VarijabilnostVariability
• Lanac od tri slojaThree-tier chain
• +3

Kašnjenje u repu i grananje pozivaTail latency and fan-out

p99 se odvaja od prosjeka; grananje poziva rep čini uobičajenimp99 decouples from the mean; fan-out makes the tail common

istraživanjeexplorer

• Rep se odvajaThe tail decouples
• Grananje na 10Fan-out to 10
• Grananje na 100Fan-out to 100
• Cilj na p99,9Target on p99.9
• +2

Kvorum i rascjep mozgaQuorum and split-brain

Većina drži jednu stranu živom; paran broj čvorova, svjedok i rascjep mozgaA majority keeps one side alive; even counts, witnesses and split-brain

korak po korakstep by step · 4 koraka4 steps

• Windows grozd sa svjedokomFailover cluster with a witness
• Dinamički kvorum i svjedokDynamic quorum and witness
• Ograđivanje (STONITH)Fencing (STONITH)
• +1

Littleov zakonLittle's law

L = λW u trgovini, na poslužitelju i u farmi za gradnjuL = λW in a shop, a server and a build farm

istraživanjeexplorer

• TrgovinaShop
• PoslužiteljServer
• Farma za gradnjuBuild farm
• Izmjeri WMeasure W
• W iz reda čekanjaW from the queue
• +3

Oluja ponovnih pokušaja i metastabilni kvarRetry storms and metastable collapse

Ponovni pokušaji drže sustav dolje; odgoda, slučajni pomak, kontrola prijemaRetries keep a recovered system down; backoff, jitter, admission control

korak po korakstep by step · 10 koraka10 steps

Raft: izbor vođe i replikacija dnevnikaRaft: leader election and log replication

Mandati, glasovi i potvrda zapisa na većini poslužiteljaTerms, votes and committing an entry on a majority

korak po korakstep by step · 4 koraka4 steps

• Raft: vođa u manjiniRaft: a leader in a minority

Replikacija s više glavnih poslužitelja: sukobMulti-master replication with a conflict

Istodobni upisi na dva glavna poslužitelja: zadnji upis, inačice, što se gubiConcurrent writes on two masters: last-writer-wins, versions, what is lost

korak po korakstep by step · 8 koraka8 steps

SLO i proračun greškeSLOs and error budgets

Brzina trošenja proračuna i uzbune za brzo i sporo trošenjeBurn rate, and fast and slow burn alerts

istraživanjeexplorer

• Ispad od 20 minutaA 20-minute outage
• Brzo trošenjeFast burn
• Sporo trošenjeSlow burn
• Kratki ispadBlip
• Ispod radaraUnder the radar
• +3

VRRP: prijelaz na pričuvniVRRP failover

Izbor glavnog, virtualna IP adresa, preuzimanje prednosti, ARP objavaMaster election, virtual IP, preemption and gratuitous ARP

korak po korakstep by step · 8 koraka8 steps

Zaostatak replikacije i preuzimanjeReplication lag and failover

Asinkrone replike kasne; preuzimanje gubi rep; čitanje vlastitih upisaAsync replicas lag; failover loses the tail; reading your own writes

korak po korakstep by step · 10 koraka10 steps

• Sinkrona i asinkrona replikacijaSynchronous vs asynchronous replication

Amaterski načini rada: referentni pregledAmateur radio modes: a reference

Analogni i digitalni načini rada s klasom emisije ITU-a i širinom pojasaAnalog and digital modes with their ITU emission class and bandwidth

pregledreference

Amplituda i perioda sinusnog titrajaAmplitude and period of a sine wave

Amplituda je visina titraja, perioda njegovo trajanje, a f = 1/TAmplitude is how far a sine swings, the period how long it lasts; f = 1/T

istraživanjeexplorer

Amplitudna modulacija (AM)Amplitude modulation (AM)

Amplituda nositelja prati NF signal; u spektru nastaju dva bočna pojasaThe carrier's amplitude follows the AF signal; the spectrum gains two sidebands

istraživanjeexplorer

Antena iznad tla: zrcalna slika i kut zračenjaAn antenna above ground: its image and the take-off angle

Tlo je zrcalo: izravni i odbijeni val zbrajaju se ili poništavaju po visiniThe ground is a mirror: direct and reflected waves add or cancel by height

istraživanjeexplorer

ASK, FSK i PSKASK, FSK and PSK

Tri načina da se bitovi utisnu na nositeljThree ways to put bits on a carrier

istraživanjeexplorer

Aurora: grub ton CW signalaAurora: the rough tone of a CW signal

Aurora u gibanju razmaže ton u šum širok stotine herca: Dopplerovo širenjeA moving aurora smears a tone into a hiss hundreds of hertz wide: Doppler spread

istraživanjeexplorer

Balansni modulator (DSB)Balanced modulator (DSB)

Izbalansiran prsten dioda potiskuje nositelj; ostaju samo dva bočna pojasaA balanced diode ring suppresses the carrier and leaves only the two sidebands

istraživanjeexplorer

Brujanje i preostala valovitostMains hum and ripple

Poluvalno ostaje valovitost 50 Hz, punovalno 100 Hz; zvučnik je čini brujanjemHalf-wave leaves a 50 Hz ripple, full-wave 100 Hz; a speaker makes it a hum

istraživanjeexplorer

Chirp u CW odašiljačuChirp in a CW transmitter

Napon VFO-a padne pri pritisku tipke, pa točke i crte počnu krivom visinom tonaWhen the VFO's supply dips at key-down, every dit and dah starts off pitch

istraživanjeexplorer

Chirp u QSO-uChirp in a QSO

Ton jedne postaje je miran, a svaka crta druge raste od pritiska tipkeOne station's tone is steady; every dah of the other rises from key-down

istraživanjeexplorer

CTCSS: tonska šumna bravaCTCSS tone squelch

Podzvučni ton otvara prijamnikA sub-audible tone opens the receiver

korak po korakstep by step · 12 koraka12 steps

• Pravi tonRight tone
• Bez tonaNo tone
• Krivi tonWrong tone
• Skriveni korisnikHidden user
• +2

Dipol kroz vrijeme: blisko polje, daleko polje i petljeThe dipole over time: near field, far field and loops

Blizu dipola silnice izlaze i vraćaju se; od oko λ/4 petlje se odvajaju i odlazeNear the dipole lines go out and back; from about λ/4 loops break away

istraživanjeexplorer

Dobitak i usmjerenost: dBi, dBd, ERP i EIRPGain and directivity: dBi, dBd, ERP and EIRP

Antena ne dodaje snagu, nego je preraspodjeljuje: stisnut dijagram, veći dobitakAn antenna adds no power, it redistributes it: squeeze the pattern, gain rises

istraživanjeexplorer

Duljina dipola: struja, dijagram zračenja i otpor zračenjaDipole length: current, pattern and radiation resistance

Struja je stojni val s nulama na krajevima; duljina pomiče napajanje po njemuThe current is a standing wave, zero at the ends; length moves the feed along it

istraživanjeexplorer

Dvije antene zajedno: razmak, faza i zakretanje snopaTwo antennas together: spacing, phase and steering the beam

Polja se zbrajaju s razlikom puta i faze: faktor niza oblikuje i zakreće snopFields add by path difference and feed phase: the array factor shapes the beam

istraživanjeexplorer

Fazna modulacija (PM)Phase modulation (PM)

Faza nositelja izravno prati vrijednost signala; kod FM to radi frekvencijaThe carrier's phase follows the signal directly; in FM, the frequency does

istraživanjeexplorer

FDMA, TDMA i CDMAFDMA, TDMA and CDMA

Tri načina da više korisnika dijeli jedan kanalThree ways to share one channel

istraživanjeexplorer

Feding (QSB)Fading (QSB)

Prizemni i prostorni val se zbrajaju; dok se faza mijenja, signal jača i slabiGround and sky wave add up; as their phase drifts, the signal swells and fades

istraživanjeexplorer

FFT i vodopadni dijagramThe FFT and the waterfall

Brzina uzorkovanja određuje raspon, veličina FFT-a razlučivostThe sample rate sets the span, the FFT size sets the resolution

istraživanjeexplorer

Filtarska metoda za SSBSSB filter method

Fiksni pojasni filtar propušta jedan bočni pojas; kvarc oscilatora bira kojiA fixed bandpass filter keeps one sideband; the oscillator's crystal picks which

istraživanjeexplorer

Fourierova sintezaFourier synthesis

Periodičan signal: zbroj sinusnih titraja na višekratnicima osnovne frekvencijeA periodic signal is a sum of sine waves at multiples of a base frequency

istraživanjeexplorer

Greyline (siva linija)The grey line

U pojasu sumraka D-regija više ne guta signal, a F-regija ga još lomi dalekoAt twilight the D region is gone but the F region still bends HF signals far

istraživanjeexplorer

I/Q kazaljkaI/Q phasor

Projekcije okretne kazaljke: vodoravno I (kosinus), okomito Q (sinus)A turning phasor's projections: I horizontally (a cosine), Q vertically (a sine)

korak po korakstep by step · 12 koraka12 steps

I/Q signaliI/Q signals

I i Q nositelji pomaknuti za 90° zbrajaju se u jedan titraj amplitude A i faze φI and Q carriers 90° apart add up to one wave of amplitude A and phase φ

istraživanjeexplorer

Kako poruka putuje kroz LoRa i mesh mrežeHow a message travels in LoRa and mesh networks

Tko prosljeđuje: gateway, svi čvorovi, samo repetitori ili svatko kao routerWho forwards: a gateway, every node, only repeaters, or everyone as a router

korak po korakstep by step · 6 koraka6 steps

Komunikacijske tehnologije: spektralni pregledCommunication technologies: a spectrum overview

Bežične tehnologije prema namjeni, smještene po frekvenciji na logaritamskoj osiWireless technologies by purpose, placed by frequency on a logarithmic axis

pregledreference

Kratke antene: otpor zračenja, gubici i širina pojasaShort antennas: radiation resistance, losses and bandwidth

Kratki dipol ugođen zavojnicom: malen, učinkovit, širokopojasan, biraj dvaA short dipole tuned by a coil: small, efficient, broadband, pick two

istraživanjeexplorer

LC titrajni krugLC resonant circuit

Energija titra između električnog polja u kondenzatoru i magnetskog u zavojniciEnergy swings between the capacitor's electric and the coil's magnetic field

korak po korakstep by step · 9 koraka9 steps

LoRa: cvrkuti i faktor širenjaLoRa: chirps and spreading factor

Faktor širenja: vrijeme u eteru prema dometuSpreading factor: time on air against range

istraživanjeexplorer

Mosni ispravljačBridge rectifier

Parovi dioda provode naizmjence; struja kroz trošilo teče u istom smjeruTwo diode pairs take turns; the current through the load always flows one way

korak po korakstep by step · 3 koraka3 steps

Od odašiljača do prijamnika: proračun vezeFrom transmitter to receiver: the link budget

Snaga i dobici, minus gušenje puta i gubici: margina iznad osjetljivosti u dBPower plus gains, minus path loss and losses: the margin above sensitivity in dB

istraživanjeexplorer

Od titrajnog kruga do anteneFrom resonant circuit to antenna

Otvoreni titrajni krug pušta polje u prostor: nastaje dipolOpening up a resonant circuit lets its field out into space: a dipole

korak po korakstep by step · 5 koraka5 steps

Packet radio i APRSPacket radio and APRS

Jedan zajednički kanal: osluškivanje, digipeateri i put WIDEn-NOne shared channel: carrier sense, digipeaters and WIDEn-N path aliases

korak po korakstep by step · 6 koraka6 steps

Polarizacija: val nosi smjer antenePolarization: the wave carries the antenna's direction

E leži u ravnini žice i spojnice; prijamni dipol uzima cos ψE lies in the plane of the wire and the line of sight; a receiver takes cos ψ

istraživanjeexplorer

Prigušni članAttenuator pad

Mreža otpornika smanjuje snagu za zadane dB, a na oba kraja ostaje 50 ΩA resistor network lowers the power by set dB and keeps 50 Ω at both ends

istraživanjeexplorer

Prioritetni promet i potvrda primitkaPriority traffic and ACK

HITNO prekida, prioritet određuje red, tek ACK isporučuje porukuHITNO preempts, priority sets the order, only an ACK delivers

korak po korakstep by step · 10 koraka10 steps

• Hitna porukaEmergency message
• Bez prioritetaNo priorities
• Četiri razineFour levels
• Nema potvrdeNo acknowledgement
• +2

Prstenasti modulatorRing modulator

Diodni prsten kao preklopka polariteta: U₃ = ±U₁ prema predznaku U₂A diode ring as a polarity switch: U₃ = ±U₁, following the sign of U₂

korak po korakstep by step · 12 koraka12 steps

Punovalni ispravljač sa srednjim odcjepomCentre-tap full-wave rectifier

Dvije diode provode naizmjence, pa obje poluperiode izlaze pozitivneTwo diodes take turns, so both half-periods come out positive

korak po korakstep by step · 3 koraka3 steps

QAM i OFDMQAM and OFDM

Veća konstelacija prema šumu; nositelji koji se ne ometajuConstellation size against noise; subcarriers that do not interfere

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QPSK u konstelacijskom dijagramuQPSK in the constellation diagram

Šum pomiče primljene točke; prijamnik bira simbol po kvadrantuNoise moves the received points; the receiver picks the symbol by quadrant

korak po korakstep by step · 16 koraka16 steps

Radijske mreže pod opterećenjemRadio networks under load

Fiksni kanali, zajednički skup ili put preko releja: tko dođe na redFixed channels, a shared pool or a route through relays: who gets through

korak po korakstep by step · 20 koraka20 steps

Radiofrekvencijski spektar: plan namjene EU/HRRadio spectrum: the EU/HR allocation plan

Tko smije koju frekvenciju: plan namjene i tehnologije od 9 kHz do 300 GHzWho may use which frequency: allocation plan and technologies, 9 kHz to 300 GHz

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Različite antene na predaji i prijamu: gubitak polarizacijeDifferent antennas at each end: polarization loss

Prijamna antena uzima projekciju vala |ê·ê*|²: pravac, elipsa ili krugThe receiving antenna takes the wave's projection |ê·ê*|²: line, ellipse, circle

istraživanjeexplorer

Shannon-Hartleyev zakonThe Shannon–Hartley law

Kapacitet kanala iz širine pojasa i omjera signal-šumChannel capacity from bandwidth and signal-to-noise ratio

istraživanjeexplorer

Skok-udaljenostSkip distance

Ravniji kut zračenja i viša lomeća regija daju dulji skok preko ionosfereA flatter radiation angle and a higher region make a longer ionospheric hop

istraživanjeexplorer

Spektar govornog signalaSpectrum of speech signals

Zvučni glasovi su crte harmonika pod formantima, bezvučni su šumVoiced sounds are harmonic lines under formants; unvoiced sounds are noise

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Spektar pravokutnog signalaThe spectrum of a square wave

Pravokutni signal: zbroj neparnih harmonika; uz skok ostaje prebačaj od oko 9 %A square wave is a sum of odd harmonics; at each jump a 9 % overshoot stays

istraživanjeexplorer

Sprega u bliskom polju: indukcija bez zračenjaNear-field coupling: induction without radiation

Blizu napon pada kao 1/r³, kao u transformatoru; iza λ/2π preuzima zračenje, 1/rClose in the voltage falls as 1/r³, like a transformer; past λ/2π radiation, 1/r

istraživanjeexplorer

SWR i stojni valSWR and standing waves

Neprilagođen teret reflektira snagu, a na vodu nastaje stojni valA mismatched load reflects power and a standing wave forms on the line

istraživanjeexplorer

Teorem uzorkovanja i aliasingThe sampling theorem and aliasing

Signal se iz uzoraka može rekonstruirati samo ako je fs > 2fA signal can be rebuilt from its samples only if fs > 2f

istraživanjeexplorer

Trap-dipolTrap dipole

Trapovi daju istoj žici različite električne duljine na različitim pojasevimaTraps give one wire different electrical lengths on different bands

korak po korakstep by step · 3 koraka3 steps

Usmjerena mreža ili svi odjednomDirected net vs free-for-all

NCS pretvara nadmetanje za kanal u red čekanjaAn NCS turns contention into a queue

korak po korakstep by step · 20 koraka20 steps

• Svi čekaju 2Everyone waits 2
• Mješovite odgodeMixed backoffs
• Sretan slučajLucky
• Usmjerena mrežaDirected net
• UsporednoSide by side
• +3

Uzorkovanje i kvantizacijaSampling and quantisation

A/D pretvarač mjeri signal u razmacima 1/fs i zaokružuje ga na 2ⁿ razinaAn A/D converter measures a signal every 1/fs and rounds it to 2ⁿ levels

istraživanjeexplorer

Valna duljina i frekvencijaWavelength and frequency

Što je valna duljina kraća, frekvencija je veća: f = c / λThe shorter the wavelength, the higher the frequency: f = c / λ

istraživanjeexplorer

Višestazno širenje i interferencijaMultipath propagation and interference

Signali s dvaju putova zbrajaju se: fazna razlika ih pojačava ili poništavaSignals from two paths add up; their phase difference makes them grow or cancel

istraživanjeexplorer

Yagi antena: reflektor, direktori i inducirane strujeThe Yagi: a reflector, directors, and parasitic currents

Napaja se samo zračitelj; ostali nose inducirane struje, faze im daje duljinaOnly one element is fed; the others carry induced currents phased by length

istraživanjeexplorer

Zamjenski NCS preuzima mrežuBackup NCS takeover

Mreža preživljava gubitak kontrolne staniceThe net survives losing its control station

korak po korakstep by step · 15 koraka15 steps

• PreuzimanjeTakeover
• Bez zamjeneNo backup
• PreranoToo early
• Bez zapisaNo log
• +2

Zašto ubrzani naboj zrači: silnice koje se lomeWhy an accelerated charge radiates: field lines that kink

Vijest o guranju putuje brzinom c i lomi silnice; lom pada kao 1/r: zračenjeNews of a push travels out at c and kinks the field lines; the kink falls as 1/r

istraživanjeexplorer

Adresni blok, rasponi i rastAddress block, ranges and growth

Od bloka do raspona i adresa za lokacije i VLAN-ove, s prostorom za rastFrom a block to ranges and addresses for sites and VLANs, with room to grow

istraživanjeexplorer

Ciklus ažuriranja na klijentuThe client update cycle

Nađi, preuzmi, instaliraj, pokreni ponovno; učestalost, rok, aktivni satiDetect, download, install, restart; scan interval, deadlines, active hours

korak po korakstep by step · 20 koraka20 steps

Delegiranje ovlastiDelegation of control

Pravo na OU-u umjesto članstva u Domain AdminsGranting rights on an OU instead of Domain Admins

korak po korakstep by step · 5 koraka5 steps

Detaljna pravila lozinki: koji PSO pobjeđujeFine-grained password policies: which PSO wins

Jedno pravilo domene iz GPO-a na korijenu; PSO-ovi ga nadjačavaju po prednostiOne domain policy from the domain root GPO; PSOs override it by precedence

korak po korakstep by step · 3 koraka3 steps

DHCP failover

Raspodjela ili vruća pričuva, MCLT i partner down; stari podijeljeni opseg 80/20Load balance vs hot standby, MCLT and partner down; the old 80/20 split scope

korak po korakstep by step · 6 koraka6 steps

DHCP upisuje klijente u DNSDHCP registering clients in DNS

Poslužitelj upisuje zapise za klijente: vlasnik, zaštita imena, DnsUpdateProxyThe server registers records for clients: owner, Name Protection, DnsUpdateProxy

korak po korakstep by step · 6 koraka6 steps

DHCP: scope, rezervacije i prednost opcijaDHCP scopes, reservations and option precedence

Isključenja, rezervacije i razine opcija: pobjeđuje najspecifičnijaExclusions, reservations and option levels: the most specific wins

istraživanjeexplorer

DNS: sigurno dinamičko ažuriranjeDNS: secure dynamic update

Klijent sam upisuje svoj zapis; vlasnik zapisa je SID, pa novi račun ne smijeClients register their own records; the owner is a SID, so a new account can't

korak po korakstep by step · 6 koraka6 steps

DNS: starenje i brisanje zastarjelih zapisaDNS: aging and scavenging

Vremenske oznake i dva intervala: koji zastarjeli zapisi nestaju i kadaTimestamps and two intervals: which stale records disappear, and when

korak po korakstep by step · 8 koraka8 steps

DNS: vrste zona i opseg replikacijeDNS zone types and replication scope

Primarna, sekundarna, stub i zona u AD-u; opseg šuma, domena ili vlastitiPrimary, secondary, stub, AD-integrated; forest, domain or custom scope

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Efektivni pristup: NTFS i dijeljenjeEffective access: NTFS plus share

Strože od dvaju pobjeđuje, zabrana je jača od dozvole, grupe se zbrajajuThe stricter of the two wins; deny beats allow; groups add up

istraživanjeexplorer

FSMO uloge: prijenos ili preuzimanjeFSMO roles: transfer or seize

Poslovi samo jednog DC-a, što pada bez nositelja; prijenos ili preuzimanjeThe single-master jobs, what breaks without the holder; transfer vs seize

korak po korakstep by step · 6 koraka6 steps

Funkcionalne razineFunctional levels

Što podizanje razine domene i šume otključava, a što isključujeWhat raising the domain and forest level unlocks, and what it rules out

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GPO: pravila i preference (tetoviranje)GPO policies vs preferences (tattooing)

Kad GPO nestane, pravilo se vraća, a preferenca ostajeWhen the GPO goes away, a policy reverts; a preference stays

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GPO: prednost i pobjednička postavkaGPO precedence: the winning setting

Lokalno → lokacija → domena → OU, redoslijed veza, prisilno i blokadaLocal → site → domain → OU, link order, Enforced and Block Inheritance

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GPO: sigurnosno i WMI filtriranjeGPO security and WMI filtering

Na koga se GPO primjenjuje; i račun računala treba čitanjeWho a GPO applies to; the computer account needs Read too

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Grupe računala i odobrenjaComputer groups and approvals

Odobrenje po grupi, rokovi; dodjela grupe na poslužitelju ili na klijentu (GPO)Approve per group, deadlines; server-side vs client-side targeting by GPO

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• Prstenovi uvođenja ažuriranjaUpdate rings

Iskorištenost i pragoviUtilisation and thresholds

Popunjenost opsega na poslužiteljima; upozorenje prije nego što se raspon napuniScope fill across servers; an alert before a range runs out

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Kada se pravila primjenjujuWhen policy applies

Pokretanje, prijava, osvježavanje svakih 90 ± 30 min, gpupdate i dvije prijaveStartup, logon, refresh every 90 ± 30 min, gpupdate, and the second logon

korak po korakstep by step · 2 koraka2 steps

Kako Windows klijent razrješava imeHow a Windows client resolves a name

hosts, predmemorija, DNS sa sufiksima, LLMNR i NetBIOS; zašto kratko ime zakažeHosts file, cache, DNS with suffixes, LLMNR/NetBIOS; why a short name goes wrong

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Kerberos: karte i satoviKerberos: tickets and clocks

AS daje TGT, TGS kartu za uslugu, AP otvara mapu; razlika satova to rušiAS gives a TGT, TGS a service ticket, AP opens the share; clock skew breaks it

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Klonovi koji se ne javljajuClients that never report

Klonovi iste slike dijele jedan client ID, pa ih WSUS vidi kao jedno računaloCloned images share one client ID, so many machines show as one

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Lokacije, veze lokacija i KCCSites, site links and the KCC

Replikacija unutar i između lokacija, trošak i raspored; izbor DC-a po lokacijiIntra-site vs inter-site replication, cost and schedule; site-aware DC choice

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Nasljeđivanje NTFS dozvolaNTFS inheritance

Naslijeđeni i izričiti unosi, isključeno nasljeđivanje, kopija i premještanjeInherited vs explicit entries, disabling inheritance, copy vs move

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NTLM i KerberosNTLM vs Kerberos

Izazov-odgovor ili karta; prelazak na NTLM; zašto pass-the-hash radiChallenge-response vs tickets; NTLM fallback; why pass-the-hash works

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Obnova DC-a i USN rollbackRestoring a DC, and USN rollback

Nemjerodavna i mjerodavna obnova; vraćanje snimke DC-a tiho kvari replikacijuNon-authoritative vs authoritative restore; snapshot reverts break replication

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Obrisani objekti: tombstone i koš za smeće AD-aDeleted objects: tombstone and Recycle Bin

Životni vijek nadgrobnog zapisa, koš za smeće AD-a i mjerodavna obnovaTombstone lifetime, the Recycle Bin and authoritative restore

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Odnosi povjerenjaTrusts between domains and forests

Smjer, tranzitivnost, povjerenje između šuma i vanjsko: tko smije kamoDirection, transitivity, forest vs external trusts: who can access what

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Opsezi grupa i AGDLPGroup scopes and AGDLP

Globalna, lokalna grupa domene, univerzalna: tko je član, gdje se koristiGlobal, domain local, universal: who can be a member, where it can be used

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OU ili grupa?OU or group?

OU nosi pravila i delegiranje, grupa dozvole; jedan OU, mnogo grupaOUs carry policy and delegation, groups permissions; one OU, many groups

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PowerShell šalje objekte, bash tekstPowerShell pipes objects, bash pipes text

Isti zadatak u dva cjevovoda: retci teksta naspram objekata sa svojstvimaThe same task in two pipelines: lines of text versus objects with properties

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• Razmak u imenu: awk ispisuje pola imenaA space in a name: awk prints half the name
• Format-Table prije Sort-Object: tablica nije poredanaFormat-Table before Sort-Object: the table is not sorted

Prijava u domenuDomain logon

Lociranje DC-a preko DNS SRV, zatim Kerberos; bez DC-a spremljene vjerodajniceDC locator via DNS SRV, then Kerberos; cached credentials when no DC answers

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Pristupni tokenThe access token

SID-ovi i grupe utvrđuju se pri prijavi; zato se nakon promjene grupe odjavišSIDs and groups are fixed at logon; why you log off after a group change

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Prosljeđivači, uvjetni prosljeđivači i root hintsForwarders, conditional forwarders, root hints

Kamo DC šalje imena koja nisu njegovaWhere a DC sends names it doesn't own

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Replikacija AD-a s više glavnih kopijaAD multi-master replication

USN-ovi, vektor ažurnosti i pobjeda zadnjeg upisa po atributuUSNs, the up-to-dateness vector, attribute-level last writer wins

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Replikacija SYSVOL-aSYSVOL replication

Verzija GPO-a u AD-u i u SYSVOL-u; GPO koji je u podružnicu stigao napolaGPO version in AD vs in SYSVOL; a GPO that half-arrived at a branch

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