Re: [mpls-linux-general] Hierarchical LSP set up
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Re: [mpls-linux-general] Hierarchical LSP set up
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From: James R. L. <jl...@mi...> - 2000-12-07 17:36:52
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I saw your post to the IETF mailing list. Have you read the draft: ftp://ftp.ietf.org/internet-drafts/draft-ietf-mpls-lsp-hierarchy-01.txt It explains the notion of a Forwarding Adacency (FA). When you establish an LSP between two LSRs, you can consider them to have a FA, thus making the LSP a FA-LSP. The FA-LSP has an identifier associated with it (IP address of some sort) When signalling a LSP that should tunnel through the FA-LSP, you signify this by contructing an ERO that has the IP address assocaited with the FA-LSP as one hop. RSVP-TE needs to then know how to send PATH and RESV messages to the far end of a FA-LSP (I'm not sure how this works). I hope this point you in the right direction. Jim PS When asking question to the IETF mailing list, the shorter the question the better. :-) Many of the people on the list will not take the time to answer long questions. On Wed, Dec 06, 2000 at 05:17:03PM +0530, Ramanjaneyulu Y T wrote: > Hi, > > I have questions on how to establish LSPs . pls go through following > mail and answer to those. > > Thanks in advance, > > > > > The following is the scenarios to establish hierarchial LSps. > > Method1 > ------- > > > > > > --------- --------- > | | | | > | LER11 | | LER12 | > | | | | > --------- --------- > | | > . Y Z . > . -------- ------- ------ T . > |__X___| | | | | |____| > | LER1 |-----| |-----.....|LER2 | > | | | | | | > -------- ------- ------ > > at LER1 at LER2 > label look up table label look up table > > X -- FWD Y Z - FWD T > > NHLFE NHLFE > > Y -- PUSH Y T -- PUSH T > > > > > > Note: > ---- > PUSH y -- PUSH label Y > FWD y -- check entry 'Y' > at NHLFE table > > The output entry it having separate operations. In this case it just > forwads to soecified interface in table. > > > --- > Initially there is no LSP existing between LER1 and LER2. When request > comes from LER11 , PATH message is sent to LER12 . When LER12 responds > with > RESV message with label for previous hop.When RESV message reaches from > upstream LSR to LER2 , it allocates new label and binds with label from > upstream LSR and propagates RESV message to previous hop. The same process > is > repeated at all LSRS and LER1 also. Now LSP is established between from > LER11 > to LER12 through LER1 and LER2. Note that this is not hierarchical LSP. > > In this case , all data transfers occurs normally. > > Consider the following scenario. > > > > > -------- --------- > | | | | > | LER11 | | LER12 | > | | | | > --------- --------- > | | > . Y Z . > . -------- ------- ------ . > |__X___| | | | | |__T_| > | LER1 |-----| |-----.....|LER2 | > ______| | | | | |_____ > |A -------- ------- ------ | > | B | > . . > . . > | > | ---------- > -------- | | > | | | LER 22 | > | LER 21 | | | > | | ---------- > -------- > > > > In this scenario, we want to set up an LSP between LER21 and LER 22 > through > LER1 and LER 2 which is a heirarchical LSP (in the sense that the same LSP > wil > be used by both the traffic flows from LER 11 and LER 21) > > Note: > ---- > LER2 generates label 'C' and informs to LER1 for LER21. > > > > at LER1 at LER2 > > label look up table label look up table > > X -- FWD Y Z - FWD T > A -- PUSH C , FWD Y C - FWD B > > NHLFE NHLFE > > Y -- PUSH Y T -- PUSH T > B -- PUSH B > > > > > > > > If LER21 wants to establish LSP to LER22. It sends PATH request to > LER22. > LER22 responds to PATH message with RESV message with label for previous > hop. > when RESV message reaches to LER2 , it generates a new label for LER1 , > LSP > is already existing between LER1 and LER2. In core LSRS between LER1 and > LER2 > , just bypasses this message. At LER1 , it generates a new label and > places > PUSH LER2 label operation in newly generated label and forwards it to > previous hop. > > > My question is , how LER2 differentiate MPLS data packets whether to > forward > to LER12 or LER22 by seeing on top label ( here 'Z'). > > Method2 > ------- > If we establish one LSP between LER1 and LER2, then we can use this > LSP to > establish LER11 and LER12 as hierarchical LSPs. same way for LER21 and > LER22. > If this is the case at LER2 , data packet contains label stack of depth 2 > . > So POP top label at LER2 and based on next label one can forward the > packet. > But for this one is required to establish LSPs statically and those 2 > nodes > should know each other. But this approach is not suitable, i think , due > to > these constraints. > > > During LSP establishment between LER11 and LER12 , the LER2 > generates > new label and informs to LER1. This is same for second LSP also. > > suppose LER2 generates M for LER12. The table update is as follows. > > at LER1 at LER2 > > label look up table label look up table > > Z - POP > A -- PUSH C , FWD Y C - FWD B > X -- PUSH M , FWD Y M - FWD T > > NHLFE NHLFE > > Y -- PUSH Y T -- PUSH T > B -- PUSH B > > > > So at LER2 , the MPLS pkt conatins M,Z or C,Z. So by looking on tables , > it > learns POP top label and looks on next label. This is works fine in > hierarchical environmant , but it has constraints. > > Questions: > --------- > > 1. Is above methods are correct ? > > 2. Other than these 2 methods any other methods avaialble to achieve > hierarchial LSPs ?. > > > > > > > > > > > > > > > Regards > Ramanjaneyulu Y.T. > -- > " A real friend is one who walks in when the rest of the world walks > out." > ------------------------------------------------------------------------------ > Y.T.RAMANJANEYULU | My other mail Ids: > E-70,INDIAN INSTITUTE OF SCIENCE | yt...@12... > BANGALORE - 560012 | ki...@ex... > PH: 91 - 80 - 3092622 ( HOSTEL ) | > 91 - 80 - 3092658 ( HFCL LAB ) | > visit my home page:www2.csa.iisc.ernet.in/~ytr > -------------------------------------------------------------------------------- > > > > > _______________________________________________ > mpls-linux-general mailing list > mpl...@li... > http://lists.sourceforge.net/mailman/listinfo/mpls-linux-general -- James R. Leu |
