Solved: What conditions static route will be installed in routing table

pengfang · ‎04-04-2008

I would clarify some basic concept.I know this maybe a silly question, but after reading a document, my concept about static route is not so clear.

Router1 e1(192.168.1.1/24)--- e1 (192.168.1.2/24) Router2 e2 (192.168.2.2/24)

Scenario 1:

R1:

ip route 192.168.2.0 255.255.255.0 192.168.1.2

Scenario 2:

ip route 192.168.2.0 255.255.255.0 e1

so I would like to know when I shut down the R1E1 and R2E1 separately in both scenarios , whether or not the static route to 192.168.2.0 will be installed in R1's routing table.

Basically, I'm not sure if the static route status in routing table is related the reachability of the interface TO the next hop router and the interface OF the next hop router.

Thanks in advance.

Richard Burts · ‎04-04-2008

Peng

The behavior of IOS about static routes is fairly clear. A static route is installed in the routing table if the interface that the router uses to reach that prefix is up. So in your example R1 will install the static route is e1 is up. It does not matter to R1 and its static route whether R2 interface is up or down.

Even if the R2 interface is down and there is no connectivity, if the R1 e1 interface is up then R1 installs the static route into its routing table.

The behavior is the same whether you configure the static route with the next hop address or with just the outbound interface.

HTH

Rick

HTH

Rick

View solution in original post

Richard Burts · ‎04-04-2008

Peng

The behavior of IOS about static routes is fairly clear. A static route is installed in the routing table if the interface that the router uses to reach that prefix is up. So in your example R1 will install the static route is e1 is up. It does not matter to R1 and its static route whether R2 interface is up or down.

Even if the R2 interface is down and there is no connectivity, if the R1 e1 interface is up then R1 installs the static route into its routing table.

The behavior is the same whether you configure the static route with the next hop address or with just the outbound interface.

HTH

Rick

HTH

Rick

mattcalderon · ‎04-04-2008

It used to be that routes that point to the physical interface has an AD of 0 where a route that points to the next hop has an AD of 1.

you could assign whatever AD you want in a static route, but by default those are your values.

**hahaa man I am only 25 but those were old days..

http://blog.ioshints.info/2007/02/not-all-static-routes-were-created.html

Richard Burts · ‎04-04-2008

Matthew

I am a bit puzzled. You post a link which correctly observes that all static routes have the same administrative distance (of 1). And then you make a comment about static routes pointing to an interface having AD of 0 (which is not correct).

The real difference in the 2 static routes is that the route pointed to the interface instead of the next hop will require that the router ARP for every destination address that it forwards to using that static route. And the success of the static route pointing to the interface depends on the neighbor router enabling proxy arp.

HTH

Rick

HTH

Rick

mattcalderon · ‎04-04-2008

Ya I remembered the AD difference had changed in older ios releases and edited my post with a document supporting that. I should have edited my original post explaining that. Thanks for the insight!

pengfang · ‎04-04-2008

Hi Rick, thanks for the prompt reply.

Richard Burts · ‎04-04-2008

Peng

I am glad that my information was helpful. Thank you for using the rating system to indicate that your question was resolved (and thanks for the rating). It makes the forum more useful when people can read a question and can know that they will read a response which resolved the question.

HTH

Rick

HTH

Rick

pengfang · ‎04-04-2008

No problem Rick, this forum is always my first choice once I have any questions, it is very helpful.