The MPLS-OPS Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Re: What decides tunneling???
... >u wud manually >identify the laabel between R1 and R2 and say "this label goes here without >popping label" manually... i mean not cli type it but well "the router has to look at it" ..bad lingo sorry :o)..and that too before popping the label.. am not too sure why R2 actually needs to pop the 1st label...mebbe to do with the fact that labels are unique on links and not on networks etc...but im think in this scenario, if r2 retained the same label it got from R1 too, it wudnt be a problem... ----- Original Message ----- From: alok <alok.dube@apara.com> To: vignesh03 <vignesh03@indiatimes.com>; <mpls-ops@mplsrc.com>; Sidnie Feit <sfeit@vnet.net> Sent: Friday, November 08, 2002 12:25 AM Subject: Re: [MPLS-OPS]: What decides tunneling??? the answer seems to be there in what u cut and paste from the RFC unless im not sure of what ur asking When P travels from R1 to R2, it will have a label stack of depth 1. > R2, switching on the label, determines that P must enter the tunnel. i think wot sidnie says is more from signalled LSPs , u wud manually identify the laabel between R1 and R2 and say "this label goes here without popping label" thats how LDP tends to make FECs too -rgds Alok ----- Original Message ----- From: Sidnie Feit <sfeit@vnet.net> To: vignesh03 <vignesh03@indiatimes.com>; <mpls-ops@mplsrc.com> Sent: Thursday, November 07, 2002 11:44 PM Subject: Re: [MPLS-OPS]: What decides tunneling??? By the time traffic is flowing, the path has been set up and all of the information that is needed is in the forwarding table. Namely (at R2) 1. Swap the level one label 2. Push on label X (which will take this packet to R21) The hard work was done earlier by the routing and label distribution protocols. The routing protocol would tell R2 that R3 was on the best route to the destination. If LDP was used, then BY CONFIGURATION, R2 would have a TCP session with remote node R3. R3 would provide a level 1 label. Again, topology knowledge would tell R2 that the best way to get to R3 was through R21, R22, and R23 (which might, for example, be ATM/MPLS nodes). So if R21 passed R2 a label (VPI/VCI) associated with reaching R3, R2 would use it. Sidnie Feit At 06:39 PM 11/7/2002 +0530, you wrote: >Pls help me out on this > >Here is an extract from RFC 3031 on tunneling. > >3.27.4. Hierarchy: LSP Tunnels within LSPs > > Consider a LSP <R1, R2, R3, R4>. Let us suppose that R1 receives > unlabeled packet P, and pushes on its label stack the label to cause > it to follow this path, and that this is in fact the Hop-by-hop path. > However, let us further suppose that R2 and R3 are not directly > connected, but are "neighbors" by virtue of being the endpoints of an > LSP tunnel. So the actual sequence of LSRs traversed by P is <R1, > R2, R21, R22, R23, R3, R4>. > > When P travels from R1 to R2, it will have a label stack of depth 1. > R2, switching on the label, determines that P must enter the tunnel. > R2 first replaces the Incoming label with a label that is meaningful > to R3. Then it pushes on a new label. This level 2 label has a > value which is meaningful to R21. Switching is done on the level 2 > label by R21, R22, R23. R23, which is the penultimate hop in the > R2-R3 tunnel, pops the label stack before forwarding the packet to > R3. When R3 sees packet P, P has only a level 1 label, having now > exited the tunnel. Since R3 is the penultimate hop in P's level 1 > LSP, it pops the label stack, and R4 receives P unlabeled. > > The label stack mechanism allows LSP tunneling to nest to any depth. > >My QUESTION is how does R2 know that it has to enter the tunnel.Is it >determined by some field in the MAC address or is it depending on the port >or HOW???? > > > >Thanx > >Vicky. > >---------- >Get Your Private, Free E-mail from Indiatimes at ><http://email.indiatimes.com>http://email.indiatimes.<http://email.indiatim es.com>com >Buy Music, Video, CD-ROM, Audio-Books and Music Accessories from ><http://www.planetm.co.in>http://www.planetm.co.in >Change the way you talk. Indiatimes presents "Valufon", Your PC to Phone >service with clear voice at rates far less than the normal ISD rates. Go >to <http://www.valufon.indiatimes.com>http://www.valufon.indiatimes.com. >Choose your plan. BUY NOW. ------- 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 |
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