Configuration Guide Configuring TCP
max-segment-size: indicates the maximum segment size, ranging from 1220 to 1440 bytes
Interface configuration mode
 Configuring Path MTU Discovery
ip tcp path-mtu-discovery [ age-timer minutes | age-timer infinite ]
age-timer minutes: Indicates the interval for a new probe after a path MTU is discovered. It ranges from 10
to 30 minutes. The default is 10 minutes.
age-timer infinite: No probe is implemented after a path MTU is discovered.
Global configuration mode
The PMTUD is an algorithm documented in RFC1191 aimed to improve bandwidth utilization. When the
TCP is applied to bulk data transmission, this function may facilitate transmission performance.
If the MSS used for the connection is smaller than what the peer connection can handle, a larger MSS is
tried every time the age timer expires. The age timer is a time interval for how often TCP estimates the path
MTU with a larger MSS. The discovery process is stopped when either the send MSS is as large as the peer
negotiated, or the user has disabled the timer on the router. You may turn off the timer by setting it to
infinite.
Configuration Example
 Enabling Path MTU Discovery
Enable PMTUD for a TCP connection. Adopt the default age timer settings.
Ruijie# configure terminal
Ruijie(config)# ip tcp path-mtu-discovery
Ruijie(config)# end
Run the show tcp pmtu command to display the IPv4 TCP PMTU.
Ruijie# show tcp pmtu
Number Local Address Foreign Address PMTU
1 192.168.195.212.23 192.168.195.112.13560 1440
Run the show ipv6 tcp pmtu command to display the IPv6 TCP PMTU.
Ruijie# show ipv6 tcp pmtu
Number Local Address Foreign Address PMTU