[c-nsp] OSPF vs BGP to customer

[Justin M. Streiner]

On Wed, 17 Aug 2005, Adam Greene wrote:

> I think I saw this covered on a past thread (problem is, I don't remember
> when) ...
>
> We need to set up a customer with redundant links to two distinct segments
> of our OSPF network. Ideally, the customer would utilize the same block of
> IP's on each link. I'm thinking the customer could run OSPF with us, or
> eBGP. BGP is going to imply more $$ for the customer, and probably more work
> for us. I'm wondering if it's worth the added time & expense.

I don't agree that simply running BGP will cost the customer more money. 
Taking two default routes or some small set of prefixes from you and 
announcing their prefix(es) to you in and of itself generally puts very 
little load on a router.  Many people equate 'running BGP' with 'running 
BGP and taking full route feeds'.

> Is it generally recommended to avoid running OSPF with customers for any
> reason?

Other posters have mentioned very good reasons not to run OSPF.  The only 
way I'd even remotely consider it is if I managed the customer premise 
router(s) that were speaking OSPF with my backbone.  It's simply too big 
of a risk to give customers a means of injecting potentially dangerous 
routing information into your backbone IGP.  Yes you can run separate OSPF 
processes to give you some degree of control over route redistribution, 
but that to me would be more headache than just running BGP.  BGP allows a 
very fine degree of control over exactly what you will and will not accept 
from the customer.

If the customer is connected only to your network and your AS is 
consistent across your backbone, your customer can run BGP using a private 
AS number, or better (if you have one) an extra public AS number that's 
used solely for 'captive' multihomed customers, like what UUNET does with 
AS7046.

jms