Re: Peering best practices advice needed.

[Patrick W Gilmore <patrick () ianai net>]

On Dec 8, 2004, at 12:56 PM, Richard Irving wrote:

> > Please forgive the simplistic nature of the query..

Actually, it is refreshing to see _operational_ questions on the list. 
:-)


> > Basically my company is multi-homed with 2 different providers in the 
> > UK, and advertising a /18. Now some colleaguges in another part of 
> > the world want to break that /18 into two /19's and advertise one /19 
> > and we advertise the other. This is fine, however we are NOT running 
> > IBGP in the core, therefore the UK customers in the /19 will not be 
> > able to reach the other /19 as there would be a loop detected through 
> > EBGP.
>
>    Pardon my simplistic solution, try dropping the /18, and -only-
> advertise the corresponding /19 from each region.

This will only work if you have separate ASNs, which would be my 
suggested solution.  In fact, even if you announce the /18 + both /19s, 
as long as each site as a separate ASN, it will work.

If they must have the same ASN for some reason, have your upstreams 
send you default route as well as a full table.  You will not see the 
"other" /19, but you will send traffic to the upstream because of the 
default and they will route it properly.

> > Now someone mentioned that we could use AS-LOOP-IN feature which will 
> > overcome this problem and allow us to route to each other via EBGP. I 
> > really think this is a bad idea but until we get an internal link - I 
> > dont see a way forward. So... anyone doing this currently in their 
> > network or have any "best practices" way round this. I want our 
> > company to be good Netizens but still be able to pass traffic between 
> > the 2 /19's.

I've never used AS-LOOP-IN.  Sorry. :(

But I have used the above solution (and static defaults), and it works 
fine.

--
TTFN,
patrick