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  • 1.  IPv6 advertising next-hop using fe80: address

    Posted 10-19-2021 05:52
    Hi there,

    I'm connecting a vMX to a route-reflector using IPv6 addresses.

    BGP session is UP.

    Router is advertising correct prefixes, but the next-hop is a "fe80::250:5600:48f:93df" address not the loopback/local-address used in configuration.

    See "show bgp sum" results at the receiver router:

       Network          Next Hop            Metric LocPrf Weight Path

    *>i2804:0f0::/32    fe80::250:5600:48f:93df

    Where the address fe80::250:5600:48f:93df should be the real router IP address.

    This address is not in the configuration, but I can see this interface

    > show interface terse

    ge-0/0/0.4              up    up   inet     A.B.C.D/28

                                       inet6    2804:0f0::3/64 


    I can't remove this address.

    Any idea? Its impossible to advertise a route to a invalid address. Next-hop just won't work.

    Thanks in advance.

  • 2.  RE: IPv6 advertising next-hop using fe80: address

    Posted 10-27-2021 09:33

    I tested this in the lab briefly and the vMX sent both a global unicast and a link-local next-hop address toward the Cisco RR in the NRLI Update.

    In my case, however, the RR didn't like the link-local address and tossed an error. However, the route using the global unicast made it into the BGP table as valid, but not best, so it wasn't usable.

    In your case, it looks like it's a usable route. So do you not have connectivity?


  • 3.  RE: IPv6 advertising next-hop using fe80: address

    Posted 10-27-2021 13:41
    All link-local addresses begin with the fe80::/64 prefix. The host portion of the address is a full 64 bits long and matches the link-local interface identifier. When an interface address is configured using the eui-64 statement, its interface identifier matches the interface identifier of the link-local address.
    This is because link-local addresses are coded according to the EUI-64 specification.

    But don't worry, the routing still works but its just hard to identify the next-hoop (external address) since it advertises itself using its local-address.

    After digging some days around, I also could not find a solution for this. Since its working, I left it as it is.

    Rafael Azevedo