Subject: Re: MPLS and fragmentation...

From: Kireeti Kompella <[email-masked]>
Date: Sun, 17 Dec 2000 22:26:51 -0800 (PST)

> > I'd be happy to write an extension to LDP for MTU discovery if people think 
> > it is necessary.

Yes, please do!

> Those with long memories may remember that ARIS could convey the LSP path
> MTU to the ingress LSR, because of the particular way that ARIS worked.
> How this feature missed being added to LDP (at least as an option) is a
> mystery to me.

Those with shorter memories can look to RSVP-TE for motivation.

That said, here's an (orthogonal) idea: add MTU to the traffic eng
parameters, and allow MTU to be a constraint.  Then, one can (if so
desired) carefully route around the low MTU links and set up large
MTU paths.

Kireeti.

---

From: [email-masked]
Date: Wed, 20 Dec 2000 00:19:09 -0000

On 14 Dec Ben wrote:
	Doing anything but silently discarding would require either a change
	to draft-ietf-mpls-label-encaps-08.txt or taking the slow path
through
the LSR.  
I think silent discard is the only viable option on at least 3 counts:
1	To ask ICMP to handle this would be a functional OAM layer
violation, ie failure is in MPLS layer, but request for failure notification
in IP layer.
2	Ultimate client layer may not be IP....so ICMP is not even an
option.
3	If failure is in the middle of transit MPLS domain carrying private
IP addresses inside LSPs (eg a VPN), then the operators IGP would not seem
able to route the ICMP indication.

neil