BGP resolvable issue

[Arvin Gan]

Ping, anyone known it ?:)

Thanks
Arvin

From: Arvin Gan
Sent: Monday, August 13, 2018 5:42 PM
To: bird-users at network.cz
Subject: BGP resolvable issue

Hi all,
   In RFC4271, If the NEXT_HOP attribute of a BGP route depicts an address that is not resolvable, or if it would become unresolvable if the route was installed in the routing table, the BGP route MUST be excluded from  the Phase 2 decision function. Actually, BGP protocol is implemented this option. I notice that  resolvable is checked with "rt->attrs->dest == RTD_UNICAST" , that mean the check is depend on the reachability of route for NEXT_HOP.  However, NEXT_HOP is a host address, not  a subnet address, the resolvable checking in VRF is depending on ARP/NDP result for NEXT_HOP, if NEXT_HOP cannot be resolved for MAC, it should be  unresolved.
   The description of RFC4271 for "resolvable", I am confused whether it includes only route reachable, not includes host address reachable, does anyone clearly understand it?

My test case:

   BGP4----------------------------------------------------------BGP4 peer
      set next hop:1560::28



BGP4 peer route table :

1560::/64            unicast [direct2 09:03:52.007] * (250)
        dev A6IF1 --------------------------------------------------------the address of interface is 1560::15/64 ,generate direct route
                     unicast [bgp4 09:24:36.872 from 1560::26] (200) [?]
        via 1560::28 on A6IF1  -------------------------------------------------------the route is resolved in BGP4 peer based in brid, but the address the interface of BGP4 peer is 1560::15, not 1560::28, NDP is not successful.

Thanks
Arvin
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