[nsp] REG: OSPF routes

From: Vinod Anthony Joseph Cherunni (vac@dsqworld.com)
Date: Mon Jan 08 2001 - 02:46:00 EST


Dear All,

Here I am once again with a query in mind. Taking a scenario having two
routers interconnected with each other over a Point-Point link, wherein
each router has a dual connection to the Internet to different upstream
ISP's. Now if I have configured two default routes in each direction as
follows -

Router A
route 1 = ip route 0.0.0.0 0.0.0.0 ISPA admin-distance = default ie 1
(Primary link)
route 2 =ip route 0.0.0.0 0.0.0.0 ISP B admin-distance = 150 (Secondary
link)

Router B

route 1 = ip route 0.0.0.0 0.0.0.0 ISPA admin-distance = default ie 1
(Primary link)
route 2 = ip route 0.0.0.0 0.0.0.0 ISP B admin-distance = 150 (Secondary
link)

Also Now I have configured both my routers to propogate a 0.0.0.0.0 route
using the "default-orginate" command into the OSPF (Single Area) domain as
External Type 1 route which has an administrative distance of 110 by
default.

The requirement is such that if the primary link in router B (route
configured with default administrative distance) fails, Then router B
should propogate the OSPF default-originate route with a high cost, so
that router A will not choose that route While router A's primary link is
also down, & ahould choose the locally available seconday route

The idea is as follows -

1. Both routers should choose the static route to the primary link locally
if available.

2. If the primary link fails in one of the routers, then the router which
is affected should use the remote router's locally available primary link.

3. If both the primary links fail on both the routers, Then each of the
router should only use its locally available secondary link.

4. If any one router even losses its locally available secondary route,
Only then it should use the seconday link available on the remote router.

The reason being all the secondary links are planned to be used for
catering to MPLS customers, & we plan to save on that bandwidth. This is a
stopgap arrangement.

A small thought, can both the routers be configured with route-maps that
would effect the administrative distances of the propagated OSPF default
routes in certain situations.

Kindly advice,

With warm regards,
Vinod.



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