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tcp mss
Configuring IP Path MTU Discovery
tcp path-mtu-discovery
Copyright © 2010, Juniper Networks, Inc.
By default, the router uses an MSS value of 536 bytes and the advertised MSS is derived
from the MTU of the transmitting interface. However, you can use the tcp mss command
to set the MSS for TCP advertisements.
Use to specify the MSS value for TCP to advertise.
NOTE: The MSS value is equal to the MTU value minus the IP and TCP
headers, so the MSS value is generally 40 bytes less than the MTU.
Use the vrfName variable to specify a VRF to which you want to assign the TCP MSS
value.
Example
host1(config-if)#tcp mss 1000
Use the no version to remove the MSS value so that the router uses the advertised
MSS derived from the MTU of the output interface.
See tcp mss
IP hosts transmit large amounts of data to other hosts using a series of IP datagrams.
To best use resources, increase performance, and avoid difficult reassembly, hosts try
to send datagrams that are as large as possible without requiring fragmentation anywhere
along the path from the source to the destination. This datagram size is referred to as
the path MTU (PMTU), and it is equal to the smallest MTU for each hop in the path.
Path MTU discovery is the process of discovering the PMTU value and using that value
when transmitting TCP packets in datagrams.
Enabling PMTU Discovery
Use the tcp path-mtu-discovery command to enable PMTU discovery on the active
virtual router.
Use to enable and configure path MTU discovery on the virtual router.
Issue the command without any keywords to enable path MTU discovery.
Issue the age-timer keyword to set the time (minutes) that TCP waits before attempting
to increase the path MTU after receiving an ICMP Too Big message or after previously
increasing the PMTU successfully (minutes2). The range of these two timers is 1–30
minutes. The timer defaults to 10 minutes.
Issue the age-timer infinite keyword to disable PMTU aging functions.
Example 1—Enables path MTU discovery
host1:VR1(config)#tcp path-mtu-discovery
Chapter 1: Configuring IP
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