[c-nsp] Loopback Advertise in OSPF

[Mark Tinka]

On Thursday 28 February 2008, Brandon Price wrote:

> Does anyone have links to some good examples of this
> configuration?

We normally cover this in regional workshops.

Will send you a link to some slides that discuss this 
routing policy, tomorrow.

> I am in the process of moving our small 
> ISP to dynamic routing and have read that this is the
> preferred method.

Yes, it is.

It scales very well because your IGP (OSPF or IS-IS) doesn't 
have to carry all the prefixes your network needs to know. 
Just the BGP next-hops, i.e., Loopbacks, along with core 
interface IP addresses for reachability to those Loopbacks.

In the case of OSPF, when used with Areas, the ability to 
scale well and keep the protocol light and fast, with 
minimal convergence times, is made possible.

You would then use iBGP to carry all the prefixes you 
assigned to your customers, individually originating them 
from the edge routers your customers are connected to. BGP 
is well-suited to handling a large number of addresses (as 
we can see today on the Internet routing table).

Using BGP in your core also means you can take advantage of 
the protocol's rich set of policy management features, 
e.g., BGP communities and other such attributes, to create 
a comprehensive internal routing policy.

Cheers,

Mark.
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