Configuring MTU Signaling in RSVP

To configure maximum transmission unit (MTU) signaling in RSVP, you need to configure MPLS to allow IP packets to be fragmented before they are encapsulated in MPLS. You also need to configure MTU signaling in RSVP. For troubleshooting purposes, you can configure MTU signaling alone without enabling packet fragmentation.

To configure MTU signaling in RSVP, include the path-mtu statement:

path-mtu {allow-fragmentation;rsvp {mtu-signaling;}}

You can include this statement at the following hierarchy levels:

[edit protocols mpls]
[edit logical-systems logical-system-name protocols mpls]

The following sections describe how to enable packet fragmentation and MTU signaling in RSVP:

Enabling MTU Signaling in RSVP

To enable MTU signaling in RSVP, include the rsvp mtu-signaling statement:

rsvp mtu-signaling;

You can include this statement at the following hierarchy levels:

[edit protocols mpls path-mtu]
[edit logical-systems logical-system-name protocols mpls path-mtu]

Once you have committed the configuration, changes in the MTU signaling behavior for RSVP take effect the next time the path is refreshed.

You can configure the mtu-signaling statement by itself at the [edit protocols mpls path-mtu rsvp] hierarchy level. This can be useful for troubleshooting. If you configure just the mtu-signaling statement, you can use the show rsvp session detail command to determine what the smallest MTU is on an LSP. The show rsvp session detail command displays the MTU value received and sent in the Adspec object.

Enabling Packet Fragmentation

To allow IP packets to be fragmented before they are encapsulated in MPLS, include the allow-fragmentation statement:

allow-fragmentation;

You can include this statement at the following hierarchy levels:

[edit protocols mpls path-mtu]
[edit logical-systems logical-system-name protocols mpls path-mtu]
Note: Do not configure the allow-fragmentation statement alone. Always configure it in conjunction with the mtu-signaling statement.