The MPLS-OPS Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Fwd: Re: Stack
Alok, the label stack I am referring to is the collection of separate 32-bit MPLS labels that could be attached to a single packet. For a normal MPLS VPN there would the the local-hop MPLS label and the end-to-end VPN label. If by chance that packet also went through a TE tunnel, during that transit there would also be a tunnel label for a total of 3 labels at the same time. Each of the labels would indicate whether it was the last in the stack using the "S" bit, or what in class I call the bottom-of-stack bit. Some writers refer to each 32-bit piece as a label stack, with the idea that the 32-bit piece is actually made up of the 20-bit actual label and 12 bits of other stuff (TTL, S bit, 3 EXP bits...). If that were so, by their definition you would have multiple stacks on a single packet. Perhaps this is the basis of your question. I find that confusing and not overly definitive, though it does allow a single descriptive term for each of the pieces. For me, the 32-bit label, when put together with other 32-bit labels, I call a label stack. Therefore, with a VPN unit, a TE unit, and the local unit, we get a stack of 3 MPLS labels, or in the rare case Jim proposed, 4 MPLS labels. For me, that is the single stack, the 32-bit pieces are the labels, and the 20-bit piece is, well, uh, the label inside the Label. That last is not a great definition (sub-label? labelette? babel?), but as long as we are all clear on what is being meant by label and label stack (for me, the 32-bit piece and the group of 32-bit pieces), that should do for now. Using my definitions, I would say there will only be one stack, and that the single stack by standard can contain any number of labels but to date no more than 4 in practice. That said, I am ready to be corrected if those who know better say so. Roger Williams >From: "alok" <alok.dube@apara.com> >To: "Roger Clark Williams" <rogerw@nordlink.com> >Subject: Re: [MPLS-OPS]: Stack >Date: Mon, 23 Dec 2002 20:17:19 +0530 >X-Mailer: Microsoft Outlook Express 5.00.2615.200 > >hmmm >did u encounter it anywhere? >and any SAR ideas like ATM to address it? > >why 4? why not "1"?? > >----- Original Message ----- >From: Roger Clark Williams <rogerw@nordlink.com> >To: MPLS-ops Mailing List <mpls-ops@mplsrc.com> >Sent: Monday, December 23, 2002 7:45 PM >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 > > >mpls-ops-request@mplsrc.com using -f > > >X-Originating-IP: [80.191.2.6] > > >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. > > > > > > > > > > > > > > > > > > > > >_________________________________________________________________ > > >MSN 8 with e-mail virus protection service: 3 months FREE*. > > > > http://join.msn.com/?page=features/virus&xAPID=42&PS=47575&PI=7324&DI=7474& >SU= > > > > http://www.hotmail.msn.com/cgi-bin/getmsg&HL=1216hotmailtaglines_eliminatev >iruses_3mf > > > > > >------- > > >The MPLS-OPS Mailing List > > >Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml > > >Archive: http://www.mplsrc.com/mpls-ops_archive.shtml > > > > ------- > > The MPLS-OPS Mailing List > > Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml > > Archive: http://www.mplsrc.com/mpls-ops_archive.shtml > > ------- The MPLS-OPS Mailing List Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml Archive: http://www.mplsrc.com/mpls-ops_archive.shtml |
|