OSPF Default route Injection

Hi All,

Recently I was working on our new data center implementation and I came across OSPF default route injection mechanism. Please refer the topology showed on the right.

I was suppose to generate a default route from WAN routers to inside the network up to the edge router. We were not getting any default route from AT&T (FYI).

Think of possible options before reading through solutions.

If I configure (default-information originate) on both WAN routers, it will not generate the default route inside as this command do not generate default route by its own. it needs a default route in routing table of WAN routers before it inject a default route in OSPF.

The other option, we were having to configure(default-information originate always) on both WAN routers and both WAN routers will inject default route in topology but in case of any WAN link down, it will add a extra hop in traffic flow. For ex:- If WAN link 1 goes down but still WAN1 router will be injecting default route in topology so the traffic reach to WAN1 router destined for outside need to travel to WAN2 router to reach outside world which is not an optimal solution.

I configured a floating static route in both WAN routers pointing to AT&T side routers interface IP address.

Like 0.0.0.0 0.0.0.0 10.0.0.2 (AT&T side WAN router interface IP is 10.0.0.2)

Now WAN1 and WAN2 both routers have default route in thier routing table. I configured default-information originate in both WAN routers. This time OSPF will inject a route inside as we have a default route in WAN routers. Bingo !!

if any wan link go down, default floating route will be removed from routing table and that WAN router will stop injecting default route inside.

There is one more way with conditional route advertisement. I will explain it in next post.

Till then...Keep Routing..