Static Route Concepts & Configuration (ICND Exam Certification Guide) Ques

Unanswered Question
Jul 27th, 2007

Hello all -

Q1 of Ch 5's "Do I Know This Already" quiz in Odom's ICND Exam Cert Guide asks: Which of the following must be true before IOS lists a route as "S" in the output of a show ip route command?

a. The IP address must be configured on an interface.

b. the router must receive a routing update from a neighboring router

c. the 'ip route' command must be added to the configuration

d. the 'ip address' command must use the 'special' keyword

e. the interface must be up and up.

I thought a,c & e, that a route is useless without an interface to use. But the answer is C, and is not corrected in the book Errata.

To test, when using NetSim, I could indeed configure a static route specifying a next-hop-router without having any interfaces configured (command used was from book p 147 'ip route 10.1.2.0 255.255.255.0 10.1.128.252'). All interfaces were 'no ip address' in 'show running-config' but the route was present there and in 'show ip route' as well.

However, on a 2500 router running 11.2(4), the static route would only show up in 'show ip route' if an interface was configured. If the interface was shutdown, the route disappeared from 'show ip route'.

So can someone please clarify the following:

1) can a static route be added and show up in 'ip route' without having a configured interface?

2) if so, why would Cisco permit this? (a route with no outgoing interface makes no sense to me)

3) did this ability change after 11.2(4)? if so, with what version?

Thanks in advance!

Kathy

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vazquez.jorge Fri, 07/27/2007 - 14:23

1) can a static route be added and show up in 'ip route' without having a configured interface?

I remember changing interface configurations while having a static route present. So I would believe inputing a static route should not be affected by a interface config change (or lack of). I will test at home and post some results for you.

mohammedmahmoud Fri, 07/27/2007 - 23:10

Hi Kathy,

This is a direct question that required 1 answer and assumed having a working configuration, and for a route to be marked as S then all that you need on a working router is a static ip route command, the problem is that you assumed that the there is no up/up interface so in such situation according to number of multiple choices allowed you can build up your scenario.

You are right that on a Cisco router the route won't be entered in the routing table unless the outgoing interface is up/up (even if the ip route was using a next-hop not an outgoing interface, the router will do the recursive lookup until finding the outgoing interface).

HTH,

Mohammed Mahmoud.

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