Using the OSPF default-information originate command with two ISPs

[baskervi]

I am working for a company that has two Internet circuits with different ISPs at two different locations for redundancy, and both Internet circuits run at different speeds. I'd like to be able to direct the majority (but not all) of the traffic through the ISP with the larger bandwith, but then failover all traffic to one ISP when the other goes down. We're currently using the "default-information originate" command, which fails over OK, but I haven't figured out how to do the load balancing. I'd appreciate your thoughts. Thank you.

[vveen]

normally ospf does equal cost load balancing. You could set your ospf cost of both links equal. the disadvantange of this is that your fat link will only be used with the slow links speed.

If you were connecting one router to both isp's you could use "traffic-share min across-interfaces" to load balance over those links. however i have no experience on that.

[chris.grammer]

One thing that you could consider is advertising the default route as and

external 1 route instead of an external 2 route(cisco default). If you advertise it as an E1

route, all routers will take into consideration the cost associated with the

default route to the router advertising the default route plus the cost of the

default route itself. Whereas if it is an E2 route, the routers just use the

cost associated with the external cost and not the path to get to the router

advertising the default route.

If you made the default route E1, then the routers closest to the advertised

routers will prefer the closest default route and their preference could then be

tweaked by adjusting the interface costs for the default route with a routemap.

By using this method, you could then control which routers use which internet

connection on a per router basis because you could control the cost the internal router

sees for the path from the internal router to the ASBR advertising the default route. The

path with the lowest cost will be prefered.

router ospf 1

default-information originate metric-type 1

[attrgautam]

And just to add you can originate the E1 route with a metric so that all the routers prefer the first default route mostly.

router ospf 1

default-information originate metric-type 1 metric 10.