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Configuring a Path MTU Check for VPNs

By default, the maximum transmission unit (MTU) check for VPN routing instances is disabled on M-series routers (except the M320 router) and enabled for the M320, T-series, and J-series routers. On M-series routers, you can configure path MTU checks on the outgoing interfaces for unicast traffic routed on VRF routing instances and on virtual-router routing instances.

When you enable an MTU check, the routing platform sends an Internet Control Message Protocol (ICMP) message when a packet traversing the routing instance exceeds the MTU size and has the do-not-fragment bit set. The ICMP message uses the VRF local address as its source address.

For an MTU check to work in a routing instance, you must both include the vrf-mtu-check statement at the [edit chassis] hierarchy level and assign at least one interface containing an IP address to the routing instance.

For more information on the Path MTU check, see the JUNOS System Basics Configuration Guide.

To configure path MTU checks, do the tasks described in the following sections:

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