Single AS multiple Dirverse Providers

Tue Jun 18 12:08:02 UTC 2013

A BGP speaker will not accept routes with its own AS in the path, nor should 
it.

Whilst a number of people have suggested using allowas-in, I'd personally not 
recommend it as loop prevention is generally a good thing - if you ever added 
a BGP speaker to one network that also had internet peerings (plus iBGP to the 
existing router) allowas-in would result in internal traffic going over the 
external link since eBGP is preferred over iBGP. You could of course prevent 
that by mangling attributes, but why create the potential work and pain for 
yourself?

Instead, I'd suggest setting up iBGP peerings for each of the upstreams, 
rewriting the next hop address of received routes to the upstream of that 
particular interface. Since it would really be pointless/wasteful to advertise 
your internet routes over iBGP, be sure to restrict it to just your own 
networks.

Doing it this way means that you can quite easily just spin up a new peering 
if you get a real backbone link, and you don't take on the downsides of using 
allowas-in.

Regards
Oliver

On Monday 10 June 2013 11:36:44 Dennis Burgess wrote:
> I have a network that has three peers, two are at one site and the third
> is geographically diverse, and there is NO connection between the two
> separate networks.
> 
> 
> 
> Currently we are announcing several /24s out one network and other /24s
> out the second network, they do not overlap.  To the internet this works
> fine, however, providers a/b at site1 do not send us the two /24s from
> site b..   We have requested them to, but have not seen them come in,
> nor do we have any filters that would prohibit them from coming in.
> 
> 
> 
> Is this normal?  Can we receive those routes even though they are from
> our own AS?  What is the "best practice" in this case?
> 
> 
> 
> Dennis Burgess, Mikrotik Certified Trainer Author of "Learn RouterOS-
> Second Edition <http://www.wlan1.com/product_p/mikrotik%20book-2.htm> "
> 
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