Richard A Steenbergen
ras at e-gerbil.net
Sun Oct 3 02:54:56 UTC 2004
On Sat, Oct 02, 2004 at 11:06:31PM +0100, Ian Dickinson wrote:
> You'd need an additional community to flag this eg. 65001:666 means to
> blackhole, 65001:6666 means to propagate it as well. I can't speak for
> others but when we blackhole the destination (as opposed to blackholing
> the source or mitigating) we often only do it in the direction from
> which the attack is coming*. Why drop globally when you can drop
> traffic from a subset of the Internet? Your victim will thank you
> if 90% of their customer base can reach them, versus none. Similarly,
> if they're multi-homed, they may well rely on you NOT propagating.
> Maybe this looks different from the perspective of a global Tier-1.
No, 65001:666 (or whatever value is chosen for a well known community, for
the sake of argument) means to set the next-hop to something that discards
packets, and otherwise propagate the route as normal. If you don't want it
to be exported in a specific direction, you add no-export or no-advertise
or just don't advertise it to peer X just like you would do with any other
route. Don't complicate the protocol unnecessarily based on your specific
assumptions of how you might or might not use a feature.
There is nothing more or less complicated about this than adding a value
to the end of http://www.iana.org/assignments/bgp-well-known-communities
and declaring it a standard blackhole community. How you use it, how you
export it, and who you accept it from, are provider specific policy
decisions. However, based on the knowledge that a blackhole community
route is no different than a regular route in its ability to cause
unreachability if incorrectly announced, I would tend to suspect that most
people would choose to allow this to be propagated globally.
Richard A Steenbergen <ras at e-gerbil.net> http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)
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