[c-nsp] EoMPLS from ME3750 to 7201 GigE sub-int

[Mark Tinka]

On Sunday 18 January 2009 09:23:04 am Justin Shore wrote:

> The MTU thing got me thinking (dangerous I know).  I set
> the MTU on Gi0/2 on 7201 back to 1500 and the VC
> immediately came up and passed traffic.  The MTU on the
> sub-int of the 7201 can't be set separately from the
> physical interface's MTU:
>
> % Non-TRISL encapsulated sub-interface
> GigabitEthernet0/2.130 does not support user settable
> mtu.

You can set the 'xconnect' MTU independently on the sub-
interface, but you'll need SRC for that:

http://www.cisco.com/en/US/docs/ios/mpls/configuration/guide/mp_any_transport_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1047362

> MPLS MTU on the sub-int or physical interface doesn't
> appear to affect EoMPLS VCs either.

That just affects how much MTU is available to the MPLS 
infrastructure.

Some vendors do allow you to ignore MTU mismatch. Whether 
that's a good or bad thing is an operational matter for your 
network. We prefer to have them similar.

> Along this same train of thought, what's best practice
> for EoMPLS links when mixed with sub-ints?  Should I
> strive to keep infrastructure links separate from
> customer links?

That's what we do, in the case of edge routers.

We'd, at least, use an edge router that has three (3) 
interfaces - 2x facing upstream to the core, 1x as the 
802.1Q trunk to customers (more for customer redundancy, 
e.t.c.).

Cheers,

Mark.
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