IP-TCP_METRICS(8)

🎀 ip-tcp_metrics(8) 🎀

the TCP metrics manual, bestie 💖

💅 NAME

okay so ip-tcp_metrics is all about managing TCP Metrics ✨

📜 SYNOPSIS

ip [ OPTIONS ] tcp_metrics { COMMAND | help }
ip tcp_metrics { show | flush } SELECTOR
ip tcp_metrics delete [ address ] ADDRESS
SELECTOR := [ [ address ] PREFIX ]

🌸 DESCRIPTION

okay so ip tcp_metrics lets you mess with the entries the kernel keeps about TCP stuff for both IPv4 and IPv6 destinations 🧚 these entries show up when TCP sockets want to share info about a destination, and they get stored in a cache that's keyed by the destination address 💜

the saved info can include metric values (which start out coming from routes), a recent TSVAL for TIME-WAIT recycling, state for the Fast Open feature, and more, bestie 🦋

lowkey important: the cache is never allowed to grow past its configured limit 🙈 so the older entries get replaced with fresh info, and sometimes they get reclaimed and reused for brand new destinations 💀

and the kernel never removes entries on its own 😭 they can only be flushed with this tool, so this is literally your job now 💅

🦋 ip tcp_metrics show - show cached entries

• address PREFIX (default) — the IPv4/IPv6 prefix or address you want to look at 👀 if you don't give a prefix, you get all the entries ✨

when you show entries, the output might include:

• age <S.MMM>sec — how long ago the entry was created, reset, or updated with metrics from sockets ⏰ the entry gets reset and refreshed when it's used with metrics from a route if those metrics haven't been updated in the last hour, and not every cached value resets the age when it gets updated, so don't be shook 🫠
• cwnd <N> — the CWND metric value 🌈
• fo_cookie <HEX-STRING> — the cookie value that came in the SYN-ACK, which Fast Open uses for the next SYNs 🍓
• fo_mss <N> — the MSS value that came in the SYN-ACK, which Fast Open uses for the next SYNs 🍓
• fo_syn_drops <N>/<S.MMM>sec ago — the number of initial outgoing Fast Open SYNs-with-data that got dropped, spotted by watching the received SYN-ACK after a SYN retransmission 😤 the seconds show how long ago the last SYN drop happened, and you can use that along with the drop count to turn off Fast Open for a little while 🫶
• reordering <N> — the reordering metric value 🔄
• rtt <N>us — the RTT metric value ⏱️
• rttvar <N>us — the RTTVAR metric value 📈
• ssthresh <SSTHRESH> — the SSTHRESH metric value 🔥
• tw_ts <TSVAL>/<SEC>sec ago — the recent TSVAL and how many seconds have passed since it got saved into a TIME-WAIT socket 🧚

🗑️ ip tcp_metrics delete - delete single entry

• address ADDRESS (default) — the IPv4/IPv6 address 💖 this one is required, no skipping it bestie 🙅‍♀️

🌊 ip tcp_metrics flush - flush entries

this command flushes the entries that match some criteria you pick 🧹

it takes the same arguments as show ✨

📚 EXAMPLES

ip tcp_metrics show address 192.168.0.0/24

shows the entries for destinations from that subnet 👀

ip tcp_metrics show 192.168.0.0/24

same thing, but the address keyword is optional so you can skip it 💅

ip tcp_metrics

showing everything is the default action, iconic 👑

ip tcp_metrics delete 192.168.0.1

removes the entry for 192.168.0.1 from the cache 🗑️

ip tcp_metrics flush 192.168.0.0/24

removes the entries for destinations from that subnet 🧹

ip tcp_metrics flush all

removes all the entries from the cache 💀

ip -6 tcp_metrics flush all

removes all the IPv6 entries from the cache but keeps the IPv4 entries safe 🫶

🔗 SEE ALSO

ip(8) 💜

🫶 AUTHOR

Original Manpage by Julian Anastasov <ja@ssi.bg> 🌷

that's the whole tea, bestie 🦋 this page came from iproute2, dated 23 Aug 2012, and it's still giving 💅✨