[c-nsp] MPLS and links with limited MTU size

Victor Sudakov vas at mpeks.tomsk.su
Sun Jan 24 02:13:00 EST 2016

Adam Vitkovsky wrote:
> > There is an IP MPLS network with MTU=1600 on all routers' interfaces.
> > There are plans to add some backup Ethernet links whose maximum frame
> > size cannot exceed 1500 (hardware limit).
> >
> If you are using MPLS routers that perform forwarding in SW you can
> test in the lab if they would be able to handle the fragmentation so
> during the failure of primary link they would have to fragment.

You cannot fragment an MPLS packet, can you? I don't see anything in
the MPLS header that could help reassemble it after fragmentation.

> Otherwise the fragmentation would have to be done on CE routers
> which is something that some customers might not be happy about.

There are even no CE routers per se in the network in question.
Customers are attached to interfaces on the PE routers (i.e. even if a
customer has some routers we don't have control over them).

Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:sudakov at sibptus.tomsk.ru

More information about the cisco-nsp mailing list