[afnog] Routing asymmetry problems

[Mark Tinka]

On Saturday, October 16, 2010 01:51:58 am Kondie Masiye 
wrote:

> You will see that having the satellite as inbound works.
> I have a suspicion that it could be something to do with
> uRPF, but I am not sure where it would have been applied
> in this case to cause this disparity.

Well, you're on the right track to suspect filtering - it 
could be either control plane filtering (BGP) or data plane 
filtering (uRPF). Hopefully not both, although with uRPF, it 
can tend to be dependent on control plane routing.

> I asked my
> terrestrial 2 provider if they or their upstream uses
> uRPF, but they asked me what that is, so I take it they
> do not use it.

That's a shame.

> By the way, if I set both outbound and inbound to
> terrestrial 2, it works.
> 
> I need some pointers on how I can sort out this problem.

Get 'terrestrial 2' to confirm that:

	a) they are actually receiving all the routes you're
	   announcing to them.

	b) that they are actually re-announcing those routes
	   to ALL their upstreams and peers WITHOUT
	   prejudice.

	c) all their upstreams and peers are receiving and
	   using those routes.

Is it possible to examine the looking glasses of your 
'terrestrial 2' upstreams? I haven't done very deep digging, 
but I'm picking up TDM (.mz) as being your current upstream 
across all my peerings and looking glass (and Interoute 
being theirs).

Also, you would do well to ensure that any prefixes you're 
announcing to the Internet are registered in a well-known 
route registry. I prefer RIPE because it's free, works well 
and is used by all the major carriers. Several others exist, 
though.

The fact that things work when in/out traffic is through 
'terrestrial 2' leads me to believe data plane filtering is 
in play. Work more closely with them on this, as it will be 
more difficult to bypass them and speak to their upstreams.

Cheers,

Mark.
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