How BGP inject a default route?

[kianhowtan]

Hi,

I got a no# of routers running IBGP, with one of the routers connecting to the ISP. But I am using static routes on my edge router to the ISP router.

So my requirement is that I want to let the edge router to inject a default route to its peer via BGP.

i will appreciate if someone can provide me with the website where i can see any sample scenario.

Thanks

[befthimi]

Hi,

I assume the edge router you are referring to is the router you have connected to the ISP. If so, you could try something like the following:

router bgp 1

no synchronization

bgp log-neighbor-changes

neighbor 11.0.0.3 remote-as 1

neighbor 11.0.0.3 update-source Loopback0

neighbor 11.0.0.3 next-hop-self

neighbor 11.0.0.3 default-originate

or

you could configure a static route for 0/0 to null0 on the edge router, unless you already have a static to 0/0 pointing to the ISP as the next hop. Then you could redistribute this static into BGP. To inject the 0/0 into BGP you need to have the command "default-information originate" under the BGP routing process. IF YOU USE THIS METHOD, PLEASE MAKE SURE YOU DO NOT ADVERTISE THIS ROUTE TO THE ISP.

have a look at the command reference for further details at:

http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1831/products_command_reference_chapter09186a00800ca69a.html

I hope this helps.

Bill

[kianhowtan]

Hi Bill,

Thanks. But need further clarification.

For the first method, do I need to create a default static route? Or putting in the "default-originate" under BGP process will be good enough. That means all its IBGP peer will direct all unknow prefixes to this edge router, rite ?

As for the 2nd method, are u saying that I should use the "default-information originate" to inject the static route into the BGP, or I should be using redistribute static?

[befthimi]

For the first method, there is no need for any static routes or redistribution. The 0/0 route should be sent to each iBGP nei with this neighbour statement.

With the second method, you need to redistribute static. However, you also need to have the default-information originate no inject the 0/0 into the BGP route table.

I think the first method is clearer/easier, but depends on your environment, number of peers, etc, etc.