[j-nsp] Layer 2 VPNs and MTU

Dermot Williams dermot.williams at irishbroadband.ie
Wed May 3 05:37:52 EDT 2006

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!


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.
> 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.

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