Link local vs global v6 next hop for BGP rotuer

[Mazur, Dariusz]

Hello Ondrej,
Thanks for quick response. Additional option to ignore link-local BGP next hops would help us a lot. We use bird as routing demon for router, and our software does not install BGP routes with link-local next hops in ASIC.

1.“gw=bgp_next_hop”  does not work for us because like you mentioned we don’t have flat network and over iBGP we receive  some routes with dummy next hop which later should resolved by local static route,
 “gw=bgp_next_hop ” reject these routes saying  “<ERR> filters, line 2827: Invalid gw address”

2. I tried bgp_next_hop= bgp_next_hop in local import filter. Like you said it does not work.  My remote iBGP is juniper and we set next hop in export filter, it still does not fix problem on local router.

router> show configuration policy-options policy-statement INTX-FRA13-EXPORT
…
term SET-NEXT-HOP_v6 {
    from family inet6;
    then {
        next-hop 2600:1488:6081:106::a;
        next term;
    }
}

Thanks,
Dariusz

On 9/20/22, 6:11 PM, "Ondrej Zajicek" <santiago at crfreenet.org> wrote:

    On Mon, Sep 19, 2022 at 01:23:28PM +0000, Mazur, Dariusz via Bird-users wrote:
    > Hello,
    > In my setup I have iBGP session with peer , and I learn v6 route. It is iBGP so we have 2 next hops global and link-local. By default bird uses link-local when route is exported to kernel. Is there any command to change this behavior and use global v6 address as BGP next hop when we export routes to kernel ?

    Hello

    The dual next hop for IPv6 routes is kind of hack and not really
    reflected in filter code, which means that bgp_next_hop attribute
    represents just global address. Therefore, you can do:

      bgp_next_hop = bgp_next_hop;

    in remote IBGP export filter to reset bgp_next_hop attribute to just
    its global address.

    I think it would not work in local IBGP import filter - we assign
    recursive immediate next hop based on bgp_next_hop when route is received
    before import filter, so later change of bgp_next_hop in IBGP import
    filter would not affect existing immediate next hop.

    You can also change immediate next hop (route attribute 'gw'), either in
    local IBGP import filter, or Kernel protocol export filter:

      gw = bgp_next_hop;

    but that would work only if you have flat network and there is no
    intermediate hop between local system and bgp_next_hop.


    We probably should just add option to ignore link-local BGP next hops ...


    > Table master6:
    > fc00:2001:100:12::/64 unicast [2001:4878:c225::1:3:2__r02.ien.labkrk01.sdn 12:57:29.076] * (100) [i]
    >                 via 2001:4878:c225::1:3:2 on eth-1\1\4
    >                 Type: BGP univ
    >                 BGP.origin: IGP
    >                 BGP.as_path:
    >                 BGP.next_hop: 2001:4878:c225::1:3:2 fe80::1:3:2
    >                 BGP.local_pref: 400
    >                 BGP.community: (20940,550)
    > 
    > Thanks,
    > Dariusz

    -- 
    Elen sila lumenn' omentielvo

    Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
    OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
    "To err is human -- to blame it on a computer is even more so."