TC-SIMPLE(8)

✨ TC-SIMPLE(8) ✨

Simple action in tc(8) 💖 the bestie of tc actions, fr

🎀 NAME

simple - basic example action 🧚

🌸 SYNOPSIS

tc ... action simple [ sdata STRING ] [ index INDEX ] [ CONTROL ]

CONTROL := { reclassify | pipe | drop | continue | ok }

💅 DESCRIPTION

okay so this one is a pedagogical example, aka it's literally here to teach you how actions work, not to be useful in your daily life 😭 no shade tho. Every single time it gets accessed, it prints the STRING you gave it, and that string can be any length you want 🫶

✨ OPTIONS ✨

• sdata STRING — the actual string it prints 🖨️
• index INDEX — an optional action index value 🔢
• CONTROL — tells tc what to do next once the action is done running. For the full tea on the possible CONTROL values, peep tc-actions(8) 👀

🦋 EXAMPLES

this example makes the kernel yell "Incoming ICMP!" every time it spots an incoming ICMP packet on eth0. The vibe check goes like this:

1. Add an ingress qdisc point to eth0 🌈
2. Start a chain on ingress of eth0 that first matches ICMP, then calls the simple action to shout 📢
3. Display stats and show that no packet has been seen by the action (zero, bestie, zero) 🙈
4. Send one ping packet to google (expect to get a response back) 🏓
5. Grep the logs to see the logged message 🔍
6. Display stats again and observe the increment by 1 ⭐

$ tc qdisc add dev eth0 ingress
$ tc filter add dev eth0 parent ffff: protocol ip prio 5 \
    u32 match ip protocol 1 0xff flowid 1:1 action simple sdata "Incoming ICMP"

$ sudo tc -s filter ls dev eth0 parent ffff:
 filter protocol ip pref 5 u32
 filter protocol ip pref 5 u32 fh 800: ht divisor 1
 filter protocol ip pref 5 u32 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1
   match 00010000/00ff0000 at 8
   action order 1: Simple <Incoming ICMP>
    index 4 ref 1 bind 1 installed 29 sec used 29 sec
    Action statistics:
        Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
        backlog 0b 0p requeues 0

$ ping -c 1 www.google.ca
PING www.google.ca (74.125.225.120) 56(84) bytes of data.
64 bytes from ord08s08-in-f24.1e100.net (74.125.225.120): icmp_req=1 ttl=53 time=31.3 ms

--- www.google.ca ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 31.316/31.316/31.316/0.000 ms

$ dmesg | grep simple
[135354.473951] simple: Incoming ICMP_1

$ sudo tc/tc -s filter ls dev eth0 parent ffff:
filter protocol ip pref 5 u32
filter protocol ip pref 5 u32 fh 800: ht divisor 1
filter protocol ip pref 5 u32 fh 800::800 order 2048 key ht 800 bkt 0 flowid 1:1
  match 00010000/00ff0000 at 8
   action order 1: Simple <Incoming ICMP>
    index 4 ref 1 bind 1 installed 206 sec used 67 sec
   Action statistics:
   Sent 84 bytes 1 pkt (dropped 0, overlimits 0 requeues 0)
   backlog 0b 0p requeues 0

🫶 SEE ALSO

tc(8) tc-actions(8)

iproute2 · 12 Jan 2015 · Linux 💜 that's a wrap, bestie, you're literally a Unix legend now 👑✨