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I have a Juniper vMX router with two interfaces: ge-0/0/0.0 facing the multicast sender and ge-0/0/2.0 facing the multicast receiver. The router receives multicast packets addressed to 232.1.1.1 on its ge-0/0/0.0 interface. While the multicast route is present:

root@CE1> show pim join
Instance: PIM.master Family: INET
R = Rendezvous Point Tree, S = Sparse, W = Wildcard

Group: 232.1.1.1
    Source: 10.1.1.10
    Flags: sparse,spt
    Upstream interface: ge-0/0/0.0

Instance: PIM.master Family: INET6
R = Rendezvous Point Tree, S = Sparse, W = Wildcard

root@CE1> show route table inet.1

inet.1: 4 destinations, 4 routes (4 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

224.0.0.0/4        *[Multicast/180] 01:35:09
                      MultiResolve
224.0.0.0/24       *[Multicast/180] 01:35:09
                      MultiDiscard
232.0.0.0/8        *[Multicast/180] 01:35:09
                      MultiResolve
232.1.1.1,10.1.1.10/64*[PIM/105] 00:57:51
                      Multicast (IPv4) Composite

root@CE1>

.. then the router discards the packets silently, i.e output counter of ge-0/0/2.0 does not increase. Forwarding table entry for 232.1.1.1,10.1.1.10 looks like this:

232.1.1.1.10.1.1.10/64
                   user     0                    indr  1048575     2
                                                 comp      595     1

RPF on both ge-0/0/0.0 and ge-0/0/2.0 is enabled. What might cause such behavior?

1 Answer 1

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Linux ping utility sent the packets with TTL 1. This was the reason why the first hop router dropped the packets. TTL can be adjusted with -t, e.g ping -t 10 ....

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