ICMPINFO(8)

💖 ICMPINFO — interpret ICMP messages 💖

okay bestie, welcome to icmpinfo, section 8 of the System Manager's Manual. it's the girl who reads your ICMP mail for you, and honestly? she's iconic for it. let's get into it 🦋

✨ NAME ✨

icmpinfo — interpret ICMP messages 💅

🌸 SYNOPSIS 🌸

icmpinfo [-v[v[v]]] [-n] [-p] [-s] [-l] [-k]

🎀 DESCRIPTION 🎀

Icmpinfo is a tool for looking at the ICMP messages received on the running host. no cap, that's literally its whole job. it can be used to detect and record 'bombs' as well as various network problems. main character energy fr fr 🔥

the output format is as follows (all on one line):

  MMM DD HH:MM:SS ICMP_type[sub-type]
     < sender_ip [sender_name] > unreach_ip [unreach_name]
     sp=source_port dp=dest_port seq=sequence sz=packet_size

in normal operation, icmpinfo will only report on "weird" packets, mainly icmp_unreachable. she's picky like that. she doesn't gossip about every packet, only the ones that are giving weird 💀

✨ OPTIONS ✨

• -v — give information about all icmp packets, excepts pings. the lowercase v is for "vibe check: casual" 😌
• -vv — give about pings too (i.e. icmp_echo_reply). now we're talking, she's opening up 🫶
• -vvv — include an ascii/hex dump of each packet. full unhinged mode, we love her for it ✨
• -n — avoid name queries - just give IP addresses. use this option when running unattended on name server hosts (to avoid possible looping). pls bestie, do not skip this on a nameserver, the looping is not cute 😭
• -p — avoid port number to service name decoding. numbers stay numbers, no translation era 💅
• -s — show the interface ip that received the packet. useful only if your host has several network interfaces. in this case an '-my_ip [my_name]' is added between the sender and unreach ip and name fields. multi-interface girlies, this one's for you 🌈
• -l — forks and use the syslog(3) facility to record events (recommended use). (root only option). recommended?? by who?? by the manpage, that's who. and she's right 💖
• -k — kills the background process started with the -l option. bye bye background process, you served 👑

💀 WARNINGS 💀

the packet decoding is planned for ICMP Unreachable outputs and might not be significant for all other Icmp types. so like, don't come for her when the other types look weird, she literally told you 🙈

output can be shorter when implied by the packet size or the icmp type. it's not a bug, it's a choice ✨

real talk though: this is decoding territory where assumptions live. icmp_unreachable is the moment she was built for. everything else is bonus content.

👑 AUTHOR 👑

Laurent Demailly <dl@hplyot.obspm.fr>. Free software. a legend, honestly, we stan 🎀

okay that's the whole page bestie! and just so you know who to thank at the end of all this: this came from dl's free utilities, version V1.11 - 28 August 1995, and the page itself lives in section 8 — the System Manager's Manual. now go read some packets, you got this 💅💖✨