04-08-2016 04:52 AM - edited 03-05-2019 03:45 AM
Hello,
In a practice lab I have two routers configured with OSPF directly connected.
I have established an OSPF adjacency and advertised a default route from each router with the "default-information originate always" command.
Each router will not inject the default route pointing to the other router into the routing table.
I have checked the OSPF database and can see two default routes listed.
Can anyone explain why each router will not inject a default route to point to the other?
Cheers,
04-08-2016 08:15 AM
Hi there,
What are the sources for the static routes? If both routers have static default routes configured then it will have a much lower AD (1) than an OSPF route (110) and will not be installed in the routing table.
http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/15986-admin-distance.html
cheers,
Seb.
04-09-2016 12:53 AM
Hi,
this seems to be an additional loop prevention check in IOS. When the 'always'-keyword is used on the local router, the default routes originated from other routers are removed from the local OSPF RIB. This has, of course, no effect on the LSDB.
When we use dynamic routing protocols we don't want them to create the "mother of all routing loops" - two routers with default-routes pointing to each other, right? So I think this is a very reasonalbe check but I couldn't find any documentation about it so far.
HTH
Rolf
09-27-2020 10:42 PM - edited 09-27-2020 10:43 PM
Gidday,
Yes I understand why this check is good, I was just looking for documentation/reference to the protection.
AD does not come into play with my test as each OSPF router did not actually have a static default.
In summary, if OSPF router advertises a default route with the "always" keyword, it will not inject a default route learnt via OSPF into its routing table.
Cheers,
Cheers,
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide