On Tue, Apr 08, 2014 at 07:11:36PM +0200, Frederik Kriewitz wrote:
On Tue, Apr 8, 2014 at 5:50 PM, Thomas Goldberg <t.goldberg77@gmail.com> wrote:
Is there any other solution for this besides doubling the iBGP connections (adding seperate blackhole only sessions with higher preference)?
We faced the same problem in the past. The preference can be set on a per route basis during the import. If you add the following line to your import filter it should do the trick for you: preference = bgp_local_pref; That way the bgp local preference is used as the bird internal preference too.
That will work, but in this case i would prefer an alternative: do not depend on recursive resolution of bgp_next_hop to blackhole route, but set blackhole destination directly in filters: if bgp_next_hop = A.B.C.D then { dest = RTD_BLACKHOLE; } In that case recursive resolution of next hop is not used and resolvability test does not apply.
Having read only the mentioned section of RFC 4271 someone might argue that bird should consider blackhole routes as resolvable too:
...
That's how it's implemented on our alcatel/cisco/juniper routers too, bird seems to be the exception here.
Well, it is debatable whether IP covered by unreachable/blackhole/prohibit routes should be considered resolvable for these purposes. I would say that semantically such addresses are more-or-less equivalent to addresses not covered by any routes.
Overall I'm a little confused about the implementation now too. If the next hop is not resolvable it shouldn't be concidered at all but bird apparently still considers blackhole routes as a last resort or with higher bird preference.
That is true, BIRD currently cannot completely suppress a route based on unreachability of the nexthop, it just make unresolvable route a lowest priority route in its preference group. -- Elen sila lumenn' omentielvo Ondrej 'SanTiago' Zajicek (email: santiago@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."