Asr9k Bride Domain MTU

[Andreas Martensson]

Hi,

Can anyone please explane when to use the parameter mtu at bridge domain level?

I am setting up a bridge-domain with jumboframes on each end (jumboframes enabled on the interfaces), and i can send/recieve 9000 byte frames even when the bridge-domain mtu is set to 1500.

I Have also tested this against a BVI interface, but in order to use jumboframes one have to enable this at the BVI interface level.

So.. when do one use the parameter?

I found this in the documentation, but i don't know if i get any wiser

Configuring Bridge Domain Parameters

To configure the bridge domain parameters, associate the following parameters with a bridge domain:

•Maximum  transmission unit (MTU)—Specifies that all members of a bridge domain  have the same MTU. The bridge domain member with a different MTU size is  not used by the bridge domain even though it is still associated with a  bridge domain.

[Alexei Kiritchenko · Accepted solution]

Hi Andreas,

bridge-domain mtu is used only for control plane signaling but does not enforce any HW path changes.

Regards,

Alex.

[manuv1984]

Hi Alexei,

                              May I know what is meant by bridge domain in vpls?  Is it a virtual collection of vrfs ? As per my knowledge for each service-id we have a seperate VFI table ? If so what is vpls insatnce ? how it relates to pseudo wires ? I am a liitle bit confused about this terminologies , Please do the needful.

[xthuijs]

A bridge domain is an L2 switching entity.

All ports (aka AC, attachment circuits) in a bridge domain can switch to each other based on the mac learning table.

Typically we design it such that the brdige domain is serving a particular vlan, but that is not necessarily the case, the AC (or EFP, ethernet flow point = l2transport subinterface) can have a range of vlans it supports, and you can mix vlans inside that BD, but that makes the design a bit more difficult.

Two link bridge domains together on separate nodes, we can use pseudo wires to connect them together.

When you put PW's in a VFI (virtual forwarding instance), split horizon is natively enabled. That means, traffic received on one PW in that VFI is never sent out another PW in that same VFI to prevent looping.

ps one additional note, we dont enforce any mtu on the AC's either. Only on the mpls core links is mtu enforced, so make sure that the mtu sizes received can be transported over the PW on the core side.

xander