[j-nsp] MTU signalling on l2circuit

Harry Reynolds harry at juniper.net
Thu Jun 2 12:26:23 EDT 2005

If I follow, the circuit should come up, and operate fine, as long as
the lesser of the two MTUs is not exceeded. L2 VPNs cannot fragment. If
the CPEs are set for different MTUs you will likely see issues with OSPF
adjacency formation (stuck in exchange mode).

It is easy to have MTU issues with Ethernet, as the default 1500 byte
MTU is easily exceeded when the CPE generate a 1500 byte frame due to
the added MPLS/VPN encap. It would be better if you can raise the MTU to
be larger than the CPE can generate and the same on both ends.


> -----Original Message-----
> From: juniper-nsp-bounces at puck.nether.net 
> [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of 
> Alexander Koch
> Sent: Thursday, June 02, 2005 9:14 AM
> To: juniper-nsp at puck.nether.net
> Subject: [j-nsp] MTU signalling on l2circuit
> Hiya,
> we run on a 6.3R2 or so, and we have trunks (GE) with high 
> MTU above 9k. Now we have other trunks in the network with normal MTU.
> Tell me, please, that I can get a l2circuit to work for one 
> GE tagged sub-int with high MTU with another GE sub-int with 
> less MTU... please, please, please. I mean obviously the MTU 
> does not have to the same on both ends, does it?
> Thanks,
> Alexander
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