[c-nsp] Mpls on fastethernet <-> atm route-bridge ip link?

Code Monkey have.an.email at gmail.com
Thu Feb 9 10:42:52 EST 2006

On 2/8/06, Sean Watkins <sean at northrock.bm> wrote:
> Hi,
> Anyone ever setup mpls on a fastethernet <-> atm route-bridge ip link?
> Ie, one side
> interface FastEthernet5/0
>  bandwidth 100000
>  ip address X.110
>  load-interval 30
>  duplex full
>  tag-switching mtu 1508
>  tag-switching ip
> .
> ...
> Service providers ATM network
> ...
> ..
> to
> interface ATM3/0.80 point-to-point
>  bandwidth 100000
>  ip address X.109
>  ip pim sparse-dense-mode
>  atm route-bridged ip
>  tag-switching mtu 1508
>  pvc 80/50
>   tx-ring-limit 3

Yes, I have this kind of setup. It's been happily running for
something like two years, with no MTU problems, both sides acting both
as P routers and PE routers (so I'm quite certain the labels go
through OK).

The thing is that betwen your two routers, you have provider
equipement, specifically one that converts ATM to Ethernet. This must
be able to do the conversion while keeping the labels intact. I don't
know if it's specifically seen to in the MPLS/ATM/Ethernet standards
that normal equipment just works, or if my equipment is something
special and cool... it's just the normal equipment one of my providers
set up (see below).

FWIW, my setup is

interface ATM4/0.1 point-to-point
 ip mtu 1500
 tag-switching mtu 1530
 tag-switching ip
 pvc xxx/xxx
   encapsulation aal5snap

interface FastEthernet1/0
 tag-switching mtu 1530
 tag-switching ip

The encapsulation has to be OK between your ATM interface and the
converter, so you can't just change them, but I think that the choice
of encapsulation might impact the labels. If the labels weren't going
through I'd have advised you to test aal5snap since it works for me.

> TDP brings the link up, and I can see lables on both sides, but there
> appears to be a MTU issue as web pages die when the switching begins.
> I verified the link can do 1500 bytes, with an extended ping with DF set
> Pinging anything bigger, dies:
> I'm trying to verify with the service provider that they support jumbo
> frames

It dies because your ip mtu is 1500.

To see if jumbo frames go through, don't worry about MPLS (turn it
off!) and try setting the ip mtu to 1508 on both interfaces.

> The service providers fastethernet port is attached to a Newbridge/Alcatel
> 36170 - anyone have any experiencing using jumbo frames on that gear?

Mine is made by Ericsson, but I'd be very surprised if your Alcatel
wasn't capable of at least 1518 (for vlans). Maybe it's simply that
your service provider simply set the mtu on the port to 1500!


More information about the cisco-nsp mailing list