Related Documentation
Configuring TCP MSS for Session Negotiation
During session connection establishment, two peers agree in negotiations to determine the IP segment size of packets that they will exchange during their communication. The TCP MSS (maximum segment size) value in TCP SYN packets specifies the maximum number of bytes that a TCP packet’s data field, or segment, can contain. An MSS value that is set too high could result in an IP datagram that is too large to send and that must be fragmented. Fragmentation can incur additional overhead cost and packet loss.
To diminish the likelihood of fragmentation and to protect against packet loss, you can use the tcp-mss statement to specify a lower TCP MSS value. The tcp-mss statement applies to all IPv4 TCP SYN packets traversing all the router’s ingress interfaces whose MSS value is higher than the one you specify. You cannot exempt particular ports from its effects.
The following sections describe how to configure TCP MSS on T Series and M Series routers and J Series Services Routers, respectively:
- Configuring TCP MSS on T Series and M Series Routers
- Configuring TCP MSS on J Series Services Routers
Configuring TCP MSS on T Series and M Series Routers
To specify a TCP MSS value on T Series and M Series routers, include the tcp-mss statement at the [edit services service-set service-set-name] hierarchy level:
The range of the tcp-mss mss-value parameter is from 536 through 65535 bytes.
To view statistics of SYN packets received and SYN packets whose MSS value is modified, issue the show services service-sets statistics tcp-mss operational mode command.
For further information about configuring TCP MSS on T Series and M Series routers, see the Junos Services Interfaces Configuration Release 11.2.
Configuring TCP MSS on J Series Services Routers
To specify a TCP MSS value on a J Series Services Router, include the following statement at the [edit system internet-options] hierarchy level:
The range of the mss-value parameter is from 64 through 65535 bytes.
To remove the TCP MSS specification, use the following command:
For more information about configuring TCP MSS and session negotiation on J Series Services Routers, see the J-series Services Router Basic LAN and WAN Access Configuration Guide.
