On Wed, Aug 3, 2016 at 11:02 AM, Christopher Morrow <
[email protected]> wrote:
>
> ....
> In the scenario where we want to enable one provider to signal to the
> other provider: "please take this action"
>
> community is the 'best' option... you can signal something meaningful with
> a community where origin/metric don't really allow you to do more than
> binary decisions.
>
> In a scenario on the wider network NOT at a peering fabric that has a
> route-server thingy... you don't really need a 'transitive' attribute
> because you're just telling your neighbor: "pls do this" to which they
> presumably have policy to do the right thing (or they may choose to ignore
> you, of course).
>
> In the scenario that includes a peering-fabric and route-server, you need
> either:
> 1) route-server to do some kinky things (ignore some forms of
> non-transitive, re-map something to the non-transitive, etc)
> 2) pass the attribute through because it is transitive.
>
> the route-server is the remote network's bgp peer, so you have to ask the
> route-server to ship stuff across to other peers...
>
There are other scenarios where cleanly having the BLACKHOLE community be
transitive, it the right thing. Besides the peering-fabric/route-server
scenario you just described, there are a number of cooperative transit
relationships, where you would properly want to transitively pass the
BLACKHOLE community.
Such as;
Two ASes we sharing transit with each other up, something like this;
(ISP1) --- (AS64500) --- (AS64501) --- (ISP 2)
Let's say AS64500 was under attack, it could announce the /32 under attack
with the BLACKHOLE community to ISP1 directly and to ISP2 through it
sharing partner AS64501. AS64501 has to transitively pass the route with
the BLACKHOLE community to ISP2.
Similarly the sharing could be done through a aggregating transit AS;
(AS64501) (ISP 1)
| /
(AS64500) -- (ISP 2)
| \
(AS64502) (ISP 3)
Similarly, AS64500 has to transitively pass the route with the BLACKHOLE
community to ISPs 1, 2, and 3;
Therefore, limiting the propagation by defining the BLACKHOLE community as
non-transitive would either inappropriately limit it's use in a number of
valid scenarios or require people to do "kinky things" like ignoring the
fact that is is suppose to be non-transitive.
I prefer it be transitive and tell people to use it carefully!
But that's my $0.02.
--
===============================================
David Farmer Email:[email protected]
Networking & Telecommunication Services
Office of Information Technology
University of Minnesota
2218 University Ave SE Phone: 612-626-0815
Minneapolis, MN 55414-3029 Cell: 612-812-9952
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