vyos-documentation/docs/_include/interface-adjust-mss.txt
2021-10-08 21:33:17 +02:00

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.. cfgcmd:: set interfaces {{ var0 }} <interface> {{ var2 }} {{ var3 }}
{{ var5 }} {{ var6 }} adjust-mss <mss>
As Internet wide PMTU discovery rarely works, we sometimes need to clamp our
TCP MSS value to a specific value. This is a field in the TCP options part of
a SYN packet. By setting the MSS value, you are telling the remote side
unequivocally 'do not try to send me packets bigger than this value'.
.. note:: This command was introduced in VyOS 1.4 - it was previously called:
``set firewall options interface <name> adjust-mss <value>``
.. hint:: MSS value = MTU - 20 (IP header) - 20 (TCP header), resulting in
1452 bytes on a 1492 byte MTU.