TC-GACT(8)

📦 version 7.3.0, in alpine 3.22, alpine 3.23, alpine 3.24, arch rolling, centos-stream 10, centos-stream 9, debian trixie, fedora 43, fedora 44, nixos 26.05, nixpkgs unstable, opensuse-leap 16.0, ubuntu questing, ubuntu resolute, ubuntu stonking

✨ gact: Generic actions in tc(8) ✨

Hiii bestie 🦋 Okay so this is the page for gact, the generic action that lives inside tc(8). It's a Linux thing, and honestly it's giving very clean energy 💅

🧚 NAME

Okay so the name is just gact, short for generic action. Simple, iconic 💖

🔥 SYNOPSIS

Here's the shape of the command. Read it like a little recipe 🍓

tc ... action gact CONTROL [ RAND ] [ INDEX ]
CONTROL := { reclassify | drop | continue | pass | pipe |
        goto chain CHAIN_INDEX |
        jump JUMP_COUNT }

RAND := random RANDTYPE CONTROL VAL
RANDTYPE := { netrand | determ }
VAL := number not exceeding 10000
JUMP_COUNT := absolute jump from start of action list
INDEX := index value used

🌸 DESCRIPTION

Okay so gact lets you reclassify, drop, pass, or accept packets. Main character energy 👑 Right now there are only two algorithms. One is deterministic, and the other uses the internal kernel netrand. Both are lowkey iconic 🫶

✨ OPTIONS ✨

  • random RANDTYPE CONTROL VAL — This one is the probability setting. It tells you the chance of taking the action, written as 1 out of VAL packets. So 1 out of every VAL packets gets the action 🎀
  • CONTROL — This is where you tell tc how to proceed if the packet matches. For all the possible CONTROL values, go check out tc-actions(8). Literally the place to go 💜

🦋 EXAMPLES 🦋

Okay now the fun part 😭 Here are the examples, all of them, ready to copy.

Apply a rule on ingress to drop packets from a given source address. Bye bye, bad vibes 🙈

# tc filter add dev eth0 parent ffff: protocol ip prio 6 u32 match ip src 10.0.0.9/32 flowid 1:16 action drop

Allow 1 out of 10 packets from the source, randomly, using the netrand generator. Lowkey a probability flex 🎲

# tc filter add dev eth0 parent ffff: protocol ip prio 6 u32 match ip src 10.0.0.9/32 flowid 1:16 action drop random netrand ok 10

Deterministically accept every second packet. Predictable and periodt 💅

# tc filter add dev eth0 parent ffff: protocol ip prio 6 u32 match ip src 10.0.0.9/32 flowid 1:16 action drop random determ ok 2

🌈 SEE ALSO 🌈

Go check these out, they're the real ones 🫶

Okay that's the whole tea 🍵 Shoutout to iproute2, last updated 11 Jan 2023, all about Generic actions in tc(8). Love you, mwah 💖🧚✨

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