RTD_BLACKHOLE overridden by matching route.

[Thomas Johnson]

I am having some difficulty blackholing a route. The route in question is
received from a multihop BGP session (emulating cymru), and I am setting
the dest attribute to RTD_BLACKHOLE. However, if the same route is received
via another BGP session, the blackhole is overriden, as shown here:

bird> show route 10.0.2.0/24 all
10.0.2.0/24        via 38.8.8.105 on em1 [bgp_cogent 17:38:53] * (100)
[AS174i]
        Type: BGP unicast univ
        BGP.origin: IGP
        BGP.as_path: 174
        BGP.next_hop: 38.8.8.105
        BGP.local_pref: 100
                   blackhole [l3_bogons 18:00:03 from 10.0.1.255] (100)
[AS3356i]
        Type: BGP unicast univ
        BGP.origin: IGP
        BGP.as_path: 3356
        BGP.next_hop: 10.0.1.255
        BGP.local_pref: 255
        BGP.community: (65332,888)

The relevant parts of my test configuration are below. Is there some trick
to making the blackhole "absolute"?

filter bgp_in_cogent {
        if ! rt_import_all(174) then reject;
        accept;
}

template bgp cymru_bogons_full {
        local as 68;
        multihop 255;
        export none;
        import filter {
                bgp_community.add((65332,888));
                dest = RTD_BLACKHOLE;
                bgp_local_pref = 255;
                accept;
        };
}

protocol bgp bgp_cogent from ebgp {
        neighbor 38.8.8.105 as 174;
        import filter bgp_in_cogent;
}

protocol bgp l3_bogons from cymru_bogons_full {
        local 162.9.5.3 as 68;
        neighbor 10.0.1.255 as 3356;
}

Thank you!
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