[j-nsp] Layer 2 VPNs and MTU

[Dermot Williams]

Arpit,

That's interesting alright - it appears that the vrf-mtu-check is enable
by default on the J4300s that we use at the CE, but not on the M-series
at the core. However, we don't add the loopback to the routing instances
for our L2VPNs, so there is no IP-enabled interface from which to send
the ICMP unreachables. I'll configure this up on our lab routers and see
how I get on - it should eliminate the need to reduce MTU on a
downstream router interface pair.

I don't think that this will help with the problem that we are having
though, unfortunately, which seems be occurring as a result of MS (and
others) essentially breaking PMTUD.

Thanks for your help,

Dermot

On Wed, 2006-05-03 at 15:20 +0530, Arpit Mittal (GR/EIL) wrote:

> Hi Dermot,
> 
> We have another command to ensure the path mtu ....
> This is applicable for traffic flowing via VRF, and applies globally to
> all the VRFs.
> 
> chassis vrf-mtu-check
> 
> Use:-
> help topic chassis vrf-mtu-check
> help reference chassis vrf-mtu-check
> 
> I hope it will help.
> 
> Regards,
> Arpit Mittal 
> Engineer 
> Ericsson India Private Limited.
> Tel : +91 124 256 08 08 / +91 124 508 08 08
> Fax: +91 124 256 54 54
> Mobile : +91 98713 74801
> E-mail :	arpit.mittal at ericsson.com
> http://www.ericsson.com 
> 
> 
> -----Original Message-----
> From: juniper-nsp-bounces at puck.nether.net
> [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Dermot
> Williams
> Sent: Wednesday, May 03, 2006 3:08 PM
> To: Fedorov, Konstantin
> Cc: juniper-nsp at puck.nether.net
> Subject: Re: [j-nsp] Layer 2 VPNs and MTU
> 
> Hi Konstantin,
> 
> Thanks for the feedback - there doesn't seem to be an analogous command
> in JunOS. The ERX supports it, I think, but we don't have one :-(
> 
> Also, as I intimated, getting the subscriber to change anything is
> something we're trying to avoid. The majority of our customers are not
> very computer literate and trying to get them to hack the registry to
> reduce MTU is a notion that would have  our CSRs wailing and gnashing
> their teeth!
> 
> Dermot
> 
> On Wed, 2006-05-03 at 13:13 +0400, Fedorov, Konstantin wrote:
> 
> > Hi,
> > 
> > Recently, I have the same problem with microsoft.com site.
> > But CPE was Cisco soho router.
> > 
> > The problem resolved when I configure Ip tcp adjust-mss 1452
> > 
> > Hope this will be useful.
> > 
> > I am beginner with juniper, so I couldn't give you equivalent command 
> > in the junos.
> > 
> > 
> > -----------------------
> > Sincerely Yours,
> > Konstantin Fedorov
> > 
> > -----Original Message-----
> > From: juniper-nsp-bounces at puck.nether.net
> > [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Dermot 
> > Williams
> > Sent: Wednesday, May 03, 2006 12:38 PM
> > To: juniper-nsp at puck.nether.net
> > Subject: [j-nsp] Layer 2 VPNs and MTU
> > 
> > Hi,
> > 
> > Hope some of you can give me some pointers on the above issue. We're 
> > in the process of deploying a significant change to our architecture. 
> > Some of this target architecture will rely on the use of Layer 2 VPNs 
> > to deliver subscribers to a Redback. Unfortunately we're hitting some 
> > roadblocks in the form of MTU and Path MTU Discovery.
> > 
> > The most obvious solution to our problem is to increase the MTU across
> 
> > our network but unfortunately that isn't an option because many of the
> 
> > links that we use for backhaul don't support jumbo frames. Asking our 
> > subscribers to decrease their MTU is a non-runner as well for customer
> 
> > support reasons.
> > 
> > We've reduced the MTU on the next-hop interfaces for our subscribers 
> > and this has alleviated some of the issues but some sites
> > (http://www.microsoft.com/) don't seem to support PMTUD properly, so 
> > they are still problematic. I'm hoping and assuming that others have 
> > come across similar issues - PPPoE, for example, should present the 
> > same challenge - so I'd appreciate if someone could give me a heads up
> 
> > on how they circumvented this problem - if at all.
> > 
> > TIA
> > 
> > Dermot Williams
> > Senior Network Engineer
> > Irish Broadband Internet Services Ltd.
> > _______________________________________________
> > juniper-nsp mailing list juniper-nsp at puck.nether.net 
> > http://puck.nether.net/mailman/listinfo/juniper-nsp
> > 
> > 
> 
> Dermot Williams
> Senior Network Engineer
> Irish Broadband Internet Services Ltd.
> 
> 
> _______________________________________________
> juniper-nsp mailing list juniper-nsp at puck.nether.net
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Dermot Williams
Senior Network Engineer
Irish Broadband Internet Services Ltd.