BGP resolvable issue

[Ondrej Zajicek]

On Tue, Aug 21, 2018 at 01:43:58AM +0000, Arvin Gan wrote:
> 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.

Hi

IMHO resolvability condition is completely unrelated to ARP/NDP. See RFC
4271 9.1.2.2, host route is resolved in the same way as regular route.
NEXT_HOP is one IP address, but resolvability check does longest-matching
prefix match to find matching prefix.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."