[c-nsp] tag-switching mtu question

[Rodney Dunn]

Unfortunately it's a pretty confusing mess as we ever allowed
that tag mtu to be configurable over the physical MTU.

In 12.2(28)SB you can't do that anymore and in an upcoming
12.4T version you will not be able to either.

CSCsc62963 
Internally found severe (Sev2) bug: Resolved (R)
Have configurable MTU Range 1500 -1530 on PA-1FE and PA-2FE

They tried to explain it here:

http://www.cisco.com/en/US/products/ps6566/products_feature_guide09186a0080629db0.html

Rodney


On Mon, Jun 19, 2006 at 02:31:41PM +0100, David Freedman wrote:
> Using the following example:
> 
> 
> [ Switch with (Jumbo frame support) ] ---> [ Router ] -- > MPLS network
> 
> 
> The router in this case is at a small remote PoP, its a 7200VXR with 
> PA-FE interfaces.
> 
> A user on the switch wants an xconnect (l2vpn) via one of the VLANs to a 
> remote destination.
> The user has a requirement to carry an additional two labels of their 
> own (8 bytes), both the Jumbo enabled switch and the MPLS core support this.
> The user is incapable of using CsC (Carrier supporting carrier) for this 
> application.
> 
> My question is how to accept the oversized ethernet frames on the Router 
> trunk interface, being a PA-FE it is incapable of having its natural MTU 
> set, but supports a tag-switching mtu.
> 
> I was wondering whether the following configuration was valid:
> 
> !
> interface FastEthernet0/0
>   description to the MPLS core
>   tag-switching mtu 1540
>   tag-switching ip
> !
> interface FastEthernet0/1
>   description To the jumbo switch
>   tag-switching mtu 1540
> !
> interface FastEthernet0/1.100
>   encapsulation dot1q 100
>   description Customer Vlan 100
>   xconnect 1.2.3.4 vc 100 encapsulation mpls
> !
> 
> 
> I wouldn't have thought it would be so easy,
> assuming it does work , what are the potential pitfalls of doing this ?
> 
> 
> Thanks in advance for any responses.
> 
> Kind Regards,
> 
> David Freedman
> 
> 
> 
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