next-hop address needs to be directly connected to the
router with a static route to be active, and policy
only evaluates active routes.
--- Bruce Cole <cole@juniper.net> wrote:
> > Does anyone know if and how Juniper implements
> something similar to Cisco's
> > BGP Conditional Advertisements. Cisco's
> Conditional advertisement is
> > useful in a multihomed network, in which some
> prefixes are to be advertised
> > to one of the providers, only if information from
> the other provider is
> > missing. This condition would indicate a failure
> in the peering session, or
> > partial reachability. So, basically routes are
> advertised only if other
> > routes disappear from table.
>
> I didn't see an actual answer to this question so
> let me try.
>
> I don't know of anything in our routing policy that
> would provide
> the exact same functionality as cisco's conditional
> advertisement.
> However you may be able to achieve what you are
> looking for by
> using static routes with the resolve keyword.
> For example, if the prefix you wish to advertise is
> 3/8 you
> could configure:
>
> routing-options {
> static {
> route 3.0.0.0/8 {
> next-hop x.x.x.x;
> resolve;
> }
> }
> }
>
>
> where x.x.x.x is an IP address that is chosen out of
> the address space
> that is advertised by one of the two providers.
> (Perhaps x.x.x.x is
> an address from your link to the provider, or maybe
> it is a more
> specific than one of the prefixes you expect to
> learn from this
> provider.)
>
> Lets assume that you also learn of 3/8 via BGP, and
> export that
> prefix to the backup provider via the policy:
>
> from {
> protocol bgp;
> route-filter 3.0.0.0/8 exact;
> }
> then accept;
>
> When the static route is active, you'll wind up not
> advertising the
> prefix since the protocol match fails. When the
> x.x.x.x address
> is missing, the static route goes inactive, and you
> advertise 3/8
> due to the protocol matching.
>
> Depending upon what you want in your RIB and FIB,
> you might want
> to get more complicated, perhaps writing an export
> policy that matches
> on the next-hop instead.
>
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