Must the MTU be the same in MPLS cloud?

[wagnerch]

Hi,

I think the P-routers are not able to generate an icmp "packet too big" back to the client of a vrf. So the PMTU-Discovery will not work, right?

So must the mtu be the same in the whole mpls cloud ??

What about carrier to carrier vpn? Must the carriers use the same mtu settings for customers vrf?

Regards,

Chris

[jhalldn]

If i understand this right...

We have configured all interfaces with "mpls mtu 1526" as minimum.

But we run on PPP (E3, E1) and GE connection.

[wagnerch]

so do you think that the mtu must be the same everywhere ?

[f.campos]

It’s necessary that the lower MTU existent in core of backbone (PE-P, P-P, PE-PE) be bigger than the MTU in the access (PE-CE, LAN-CE). That is, the MTU in the Core has to support at minimum a frame of 1526 Bytes (in the case of VPN/MPLS).

[wagnerch]

that is what I thought, thanks.