The MPLS WG Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] [mpls] context labels
> a question on the context label, where would it go? It has to be above (i.e., closer to the top of the stack) the UA label for which it provides the context. On an ethernet, if the ethertype indicates "UA label", the context label would be expected to be at the top of the stack, with the UA label beneath it. On a MP2MP LSP, the downstream-assigned label assigned by mLDP would be at the top, and beneath it would be the context label and then the UA label. > Normally when a label is propped you can forget it, because the next label > in the stack is unique Well, not necessarily. If it is known, for example, that when a packet is received from interface X its top label is looked up in an interface- specific label space determined by X, then the label is not "unique", it's only unique relative to X. We've always allowed the scope of uniqueness to be determined by the incoming interface. If we allow the "incoming interface" to be the context in which a label is interpreted, why not generalize and allow an LSP egress to use "incoming LSP" as the context? When using UA labels over a P2MP LSP, we don't use PHP on that LSP, so at an LSP egress of the P2MP LSP, the top label identifies the LSP (implicitly identifying the transmitter), and hence provides the context in which to interpret the next label, which is the UA label. It's just a short step to the generalized notion of context label that I proposed in Montreal. > This strikes me as being different from the normal behavior of an LSR Think of it as a way of providing a 40 or 60 bit label space ;-) This is a change to the forwarding path and existing LSRs may not necessarily be able to handle it. _______________________________________________ mpls mailing list mpls@lists.ietf.org https://www1.ietf.org/mailman/listinfo/mpls
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