Routing

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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 

                                                       fe80::250:5600:48f:93df/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 25 days ago
    Hi, 

    this is expected, the link local address is configured automatically when you configure inet6 on an interface, and protocols like the link local more than the actual IP, you can see this with OSPF for instance, you will notice that all the next-hops for any giving link in OSPF will have a FE80(link-local) next-hop. 

    you cannot disable the link local address, but you can manually configure a different one. bear in mind also, that link local is meant to be use on a p2p link basis, meaning that this IP cannot be advertised to a distant node using a routing protocol. 

    Thanks.

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

    Posted 22 days ago
    I actually show how the link local fe80 address is naturally, and solely used within the IS-IS IGP in this SRv6 video.  Granted, it's Cisco's IOS-XR, but this speaks to the topic you mention about routing protocols using the FE80 addresses for neighborship.

    https://youtu.be/SrryHbjpnAc

    ------------------------------
    Aaron Gould
    Senior Network Engineer
    aaron@gvtc.com
    https://www.linkedin.com/in/agould123/
    ------------------------------



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

    Posted 21 days ago
    Hi,

    I guess your RR and vMX are directly connected. On vMX side, you may check 

    - Advertised next hop: "show route advertising-protocol bgp <IPv6 of your RR>"
    - In your bgp config, do you have a local-address configured for the BGP session with RR ?

    Regards,
    C


    ------------------------------
    CHRISTOPHE LEMAIRE
    ------------------------------