Routing

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about the routing table "mpls.0"

  • 1.  about the routing table "mpls.0"

    Posted 10-19-2011 07:08

    what's means about "(S=0)"in the output

     

     


    mpls.0: 7 destinations, 7 routes (7 active, 0 holddown, 0 hidden)
    + = Active Route, - = Last Active, * = Both

    0                  *[MPLS/0] 01:37:25, metric 1
                          Receive
    1                  *[MPLS/0] 01:37:25, metric 1
                          Receive
    2                  *[MPLS/0] 01:37:25, metric 1
                          Receive
    300032             *[LDP/9] 00:29:39, metric 1
                        > to 10.0.8.5 via em3.66, Pop     
    300032(S=0)        *[LDP/9] 00:29:39, metric 1
                        > to 10.0.8.5 via em3.66, Pop     
    300048             *[LDP/9] 00:29:14, metric 1
                        > to 10.0.8.10 via em2.55, Pop     
    300048(S=0)        *[LDP/9] 00:29:14, metric 1
                        > to 10.0.8.10 via em2.55, Pop  

     

    thanks a lot!



  • 2.  RE: about the routing table "mpls.0"

    Posted 10-19-2011 20:26

    Check this out

    http://www.juniper.net/techpubs/en_US/junos10.0/information-products/topic-collections/nog-mpls-model/mpls-layer-verifying.html 

     

    There are two entries per route because the stack values in the MPLS header may be different. For each route, the second entry 300032 (S=0) and 300048 (S=0) indicates that the stack depth is not 1, and additional label values are included in the packet. In contrast, the first entry, 300032 and 300048 has an inferred S=1 value which indicates a stack depth of 1 and makes each label the last label in that particular packet. The dual entries indicate that this is the penultimate router.

     

    HTH

    /Fox



  • 3.  RE: about the routing table "mpls.0"

     
    Posted 09-13-2019 00:33

    "S=0" basically means that the label is not at the bottom at the label stack, and that there are more labels to follow. There are situations when a packet would contain more than 1 label, with each meant to achieve a different objective. In such scenario, we can choose our router to treat such a packet differently, in comparison to packets that have only one label ( "S=1", not shown in the above output, but is implicit for the other routes that do not have "S=0"). This is the reason 2 entries are present in the routing table for the same destination prefix.

     

    HTH 

    Vishal