[c-nsp] IOS XR mtu changes and OSPF

[John Neiberger]

I just noticed something that I thought was interesting. In IOS, at least
on the platform and image I tested, changing an interface MTU after an OSPF
adjacency is full will not affect the adjacency. So, if you need to change
a link MTU after OSPF is up and running, it should not affect routing.

However, XR seems to behave differently. I just changed the MTU on some
links on a router running IOS XR and it caused a routing flap. Why would
OSPF flap due to an MTU change that occurs after the adjacency is up? Is
this something specific to XR or am I just confused?  :-)