[nsp] ospf default routes and bgp injection

[Christopher J. Wolff]

Hello,

In the example below, Router A receives a full routing table via BGP.
Router A, Router B and Router C are members of ospf area 0.  There are no
static routes in this network at this time.

ISP---Router A---Router B---Router C

If I understand correctly, Router C can connect to the ISP through Router B
if one of the following conditions are met:

1. Router A redistributes its BGP table into the ospf area 0.
2. Router B advertises its default route to router C using
default-information originate.
3. Router A advertises 0.0.0.0 to all members of area 0 since its
configuration specifies default-information originate always.

Accordingly,

If we choose option 1, Router A redistributes its BGP table into the ospf
area, all routers need to have magnificent amounts of memory.

With option 2, If router B advertises its default route, it becomes default
gateway for all current and new ospf area 0 members, which is not desirable.

With option 3, If router A advertises 0.0.0.0, this example would be broken
when I add router D and E to area 0, right?

ISP-A/BGP---Router A---Router B---Router C
		| (igp)
ISP-B/BGP---Router D---Router E

Any advice will be appreciated.  Thank you for your time.


Regards,
Christopher J. Wolff, VP CIO
Broadband Laboratories, Inc.
http://www.bblabs.com