The MPLS-OPS Archive

[Roger Clark Williams <rogerw@nordlink.com>]

No, I am saying that the 4 byte label (or multiples of that) gets added to 
the 1500 bytes. That is what can cause the problem in non-MPLS-aware 
equipment. And if the MTU is set for 1500 or anything less AND the packet 
is marked Do-Not-Fragment, then the packet will be dropped. These are two 
somewhat different points. And you are quite right:There will be a problem 
if the sysops of the network do not take this into consideration with the 
older or non-MPLS-aware gear.

Roger Williams


>From: Saifulazza <Saifulazza@vads.com>
>To: Roger Clark Williams <rogerw@nordlink.com>
>Subject: RE: [MPLS-OPS]: Stack
>Date: Thu, 26 Dec 2002 09:51:55 +0800
>X-Mailer: Internet Mail Service (5.5.2653.19)
>
>
>Hi Roger
>
>Are you saying that the shim header " tag bits " which equivalent to 4 byte
>will take the 4 byte out of the payload byte . Meaning if the payload is
>1500 , than when  shim header is added the total payload become 1496 . So
>for a packet with DF bit on and the packet size is 1500 , it will have
>problem to pass through . An application that create such problem is Lotus
>Notes .
>
>Cheers
>SaifulAzza Sidek
>Senior Network Engineer
>VADS BHD
>603-7712-8011
>
>
>-----Original Message-----
>From: Roger Clark Williams [mailto:rogerw@nordlink.com]
>Sent: Monday, December 23, 2002 10:16 PM
>To: MPLS-ops Mailing List
>Subject: Fwd: [MPLS-OPS]: Stack
>
>
>Amir, in a private question to Jim Guichard I asked the same question, just
>posed a different way: What are the total number of possible scenarios
>labels are used for these days? Generally, the stack wouldn't go more than
>3 deep (VPN label, MPLS local label, TE tunnel label), but Jim did present
>a rare possible scenario with 4 labels.
>
>It is my understanding there is nothing in the standards that specifically
>limits the label depth, but there could be physical limitations of the gear
>in a given network that would limit the label stack that could cross a
>network. For instance, if the packet were labelled Do Not Fragment (DF) and
>the link MTU size was less than the packet size, the packet would be
>dropped. Normally this wouldn't be an issue for MPLS-aware gear, but for
>other/older gear it may well be a concern. You can ping IP across each hop
>but no VPN traffic will cross? Look for this issue as a possible problem.
>
>I hope this helps
>
>Roger Williams
>
>
> >Resent-Date: Sun, 22 Dec 2002 07:49:30 -0500
> >X-Authentication-Warning: host.secure4-hosting.net: mplsrc12 set sender to
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> >From: "Amir Reza Minagar" <aminagar@hotmail.com>
> >To: mpls-ops@mplsrc.com
> >Date: Sun, 22 Dec 2002 15:50:00 +0330
> >X-OriginalArrivalTime: 22 Dec 2002 12:20:00.0588 (UTC)
> >FILETIME=[72D9D0C0:01C2A9B4]
> >Subject: [MPLS-OPS]: Stack
> >Resent-From: mpls-ops@mplsrc.com
> >X-Mailing-List: <mpls-ops@mplsrc.com> archive/latest/5042
> >X-Loop: mpls-ops@mplsrc.com
> >Resent-Sender: mpls-ops-request@mplsrc.com
> >
> >Dear All,
> >
> >Does anybody know if there is a maximum on the length
> >of the stack in MPLS packets?
> >
> >Regards,
> >Amir.
> >
> >
> >
> >
> >
> >
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