[c-nsp] Sup2T MPLS-TE - Strange issue with MTU selection

[James Jun]

Hi Mark,

> Sounds like there is a link somewhere in the path with 1500 MTU.
> I would check everything in the path.

Yes, I have tested fully in both directions -- I can definitely guarantee that all interfaces throughout the entire path is 9216-clean and I am able to ping between all routers with s
ize=9000 and df-bit set.  

> And verify the path is what you think it is.
> Remember tunnel paths are not necessarily symmetrical.
> 

The problem is definitely with this box; if I spawn another TE tunnel to a directly adjacent neighbor (thus there is no other link somewhere that could have 1500 in the path, it's directly attached interface to the router next to it), it too shows up as MTU=1500 in 'sh mpls interface detail' output.  The problem here is any tunnels originated by Sup2t thinks transport mtu is 1500 on any TE tunnels originated by it, even to directly neighboring router with mtu=9216 interface.  Now, if you look at the return-path (the 'other' unidirectional LSP) coming back to Sup2T from the other router, they all see MTU=9216 on their 'show mpls interface' output.

I think I'm hitting a bug somewhere.. Like I said, this wasn't a problem before until very recently where the only change that was made was an addition of 6704-10g card into the chassis.

Best,
James