Usage Guidelines Path MTU Discovery is a method for maximizing the use of available bandwidth in the network between the end points of a TCP connection. It is described in RFC 1191. Existing connections are not affected when this feature is turned on or off.

Customers using TCP connections to move bulk data between systems on distinct subnets would benefit most by enabling this feature. This might include customers using RSRB with TCP encapsulation, STUN, X.25 Remote Switching (also known as XOT, or X.25 over TCP), and some protocol translation configurations.

The age timer is a time interval for how often TCP re-estimates the Path MTU with a larger MSS. By using the age timer, TCP Path MTU becomes a dynamic process. If 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 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 can turn off the age-timer by setting it to infinite.

Examples The following example enables Path MTU Discovery:

ip tcp path-mtu-discovery

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