Hello Everyone,
Having a discussion with my co-workers about "originating a default route"..
Here is the scenario:
Let's say that within an ISP Network, there are 2 routers that act as the edge..
And 2 normal routers just below them that have iBGP sessions with the rest of the Network..
Meaning that these two edge routers receive the full routing table..
In an ISP Network, I believe it to be custom to have these 2 routers who have the full routing table originate the default route within the IGP, (ISIS for example since ISIS is normally the IGP used within a ISP Network.)
Why? Well let's say you don't want the full routing table to be flooded within the network, for obvious reasons..
That's why, I think that this approach would be the best..
The question I want to ask is surrounded around a different topic..
What about if this network is used as a backbone for other services, and these services use the backbone to reach one another other (pure IP routing no MPLS).
Let's say that for these services to reach the IP backbone, they depend on an EBGP session to pass them a "default route",
Which method would be best??
1. Originate the default route in the neighbor x.x.x.x bgp command towards these services, (since it's used only to allow access into the backbone, then pure routing occurs)
2. Originate the default route in BGP on the 2 Edge routers and allow them to flood the 0.0.0.0 network throughout the network and pass the 0.0.0.0 network through policy based routing towards these EBGP peers. (so basically the 0.0.0.0 would be seen by both protocols in the network)
3. Originate the default on the "normal routers" towards all the routers in the ISP core network, then eventually pass the 0.0.0.0 network to EBGP peers who need access to the backbone..
What do you think??
Mavrick
