CCIE Lab question strategy for passive interfaces

Unanswered Question
Aug 6th, 2008

Hi all,

I'm currently preparing for the CCIE R&S lab and cannot seem to get a clear feel for the possible requirement to "NOT actively run a routing protocol on interfaces if not necessary". The prep workbook I am working with does not provide a clear answer over the many cases provided, perhaps any of you can tell me your thoughts on the matter?

In plenty of the prep labs there are configuration questions such as:

"enable EIGRP on Loopback0 and FastEthernet 0/0"

Background info here is that there is NO neighboring EIGRP router on the Fa0/0 segment.

1. My first reaction here would be to make the fa0/0 interface passive. The only way to enable eigrp on an interface would be to use the <network> statement, telling the eigrp process to run on that interface. Does making the interface passive directly go against either of the requirements here?

2. What do generally do with loopback interfaces that are added through the <network> statement. Since these loopbacks are generally not used for routing, should they be made passive by default? Sometimes the workbook solutions do this, sometimes not.

I realize that these may be things to ask the Proctor, then again, he/she may not answer conclusively, creating the possibility of failing the points. Any ideas or better yet conclusive answers would be very helpful!!!



I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3.7 (3 ratings)
4rmorris Wed, 08/06/2008 - 17:48

The key thing is: don't do anything you aren't asked to do. You're over thinking this question.

Passive interface doesn't exactly turn off routing for the interface, the router still advertises the subnet, it just doesn't make adjacencies with other routers on that network (because it doesn't send hello packets).

Regarding your question: it asked you to turn on routing, so turn it on with the network interface. If it asked to not allow adjancencies, or not to learn any routing information on that interface, then make it passive.

For the loopbacks... why make them passive? The router can't learn any weird routes on loopback interfaces. So again, unless the question is asking you not to send hellos on the loopback, just turn on routing and away you go.

For any question, read the question and answer it exactly. If you spend too much time thinking about little things like this and tweaking your config, you'll run out of time and possibly break something later on.

Good luck,


jim_berlow Thu, 08/07/2008 - 12:29

I agree with Ryan 100% on this, but wanted to add that during the actual lab if you have questions ask the proctor. They do expect you to do what is asked on the test and if they feel you have enough information they might just tell you that you have enough info to figure it out.

reinierhamstra Thu, 08/07/2008 - 19:45

Hi Ryan,

Thanks for that. I'm certainly hoping the actual test will allow for the "don't do anything you aren't asked to do" approach. I find there is quite some ambiguity in the prep materials.

Overthinking this despite your answer;-) :

In this specific case for Fa0/0 I think the interface should be made passive however. As you stated, making it passive does not not DISABLE eigrp for the interface, it's just that no routing will be done over the interface. The routing protocol would not be actively running over the interface, eventhough it is included in the process. Making it passive would then fulfill both requirements (the first being to not "actively" run a routing protocol on interfaces if not needed).

As for the loopback interfaces I would now

tend to agree with you. There is little point

in making them passive, so perhaps the best

strategy would be to simply leave them as is,

unless told otherwise.

Thanks again for taking the time to help.



4rmorris Fri, 08/08/2008 - 05:20

Hi Reinier,

Good points. Another approach (for the uber-paranoid), is to use "passive interface default" and the "no passive interface" for all the interfaces you want routing relationships. This guarantees you don't get routing where you don't want it, but requires you to remember to turn it on if you need it, which could lead to unnecesary troubleshooting.

Good luck with your studies!


reinierhamstra Fri, 08/08/2008 - 08:52

Hi Ryan

Lol, that approach has my name written all over it! ;-)

Thanks again,



This Discussion