Peering best practices advice needed.

Wed Dec 8 18:08:05 UTC 2004

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