The MPLS WG Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Re:What to do with an illegal label stack?
Hi Zizz, If the MPLS forwarding plane receives a label stack which is illegal, it will silently (ideally it should) process the upper layer of the label stack, WITHOUT checking for the validity/presence of the "S" bit. The reason for this behaviour is that if the forwarding plane checks everytime about the sanity of the label stack, the desired feature of MPLS (i.e. fast switching using labels) will not be achieved in practice. Therefore, the better idea is to keep the responsibility of assigning/determining the correct label stack, with the LDP (or any other label distribution protocol). The control plane of every LSR, participating in the label distribution process should keep this check. Further, avoiding such errors is a must, since a case may arise, when the MPLS forwarding plane will process the "header of IP packet" assuming it to be the next layer of the label stack(when the S bit is not set in the bottom of the stack.) Hope that was useful to you, regards, -- Hemant ------------------------------------------------------ An MPLS packet arrives with a label stack with no bottom of stack bit set (e.g. 88 47 22 22 20 60 00 00 00 00 00 00...). Is any behavior mandated here? Is it OK to forward this packet, or must it be discarded? -Zizz |
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