Configure 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), you can configure path MTU checks on the outgoing interfaces for unicast traffic routed on Layer 3 VPN (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.

To configure path MTU checks, do the following:

• Enable Path MTU Check for a VPN Routing Instance
• Assign an IP Address to the VPN Routing Instance

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