Passive-interface ????

chinaman

Hello Guys,

I would like to ask for a help regarding RIP. I understand how RIP works but there is a one thing I can't understand. Regarding Passive-Interface
can you explain it to me how it works and why use this command.

Thanks.
Regards
Chinaman

johnnynodough

Issuing a passive-interface command will allow for an interface to be included in a network statement (recieve route updates, attached subnet to be advertised as a route) but it will not send updates. Good examples are segments that are stubs (one way in, one way out, no need for routing update traffic) and ISDN backup links that dont need to go (or stay up) up every 30 seconds when RIP sends updates.

chinaman

Thanks, but still its not clear. Anyway I really appreciate your help.
One thing I understand in your explanation is that when issuing a passive interface command to an interface it wil include the following (routes, attached subnet to be advertised) but in stub it will net send the updates.

Chinaman

EdTheLad

Hey Chinaman, maybe you'll understand this a little better.
As you know RIP is a classful routing protocal,when you want to assign interfaces to the Rip process you need to specify its classful IP address.
If you have 2 interfaces on your router each with an IP address
151.98.25.5/30 and 151.98.25.9/30 these would be assigned using the network command as follows.
routerA(config-router)#network 151.98.0.0, the problem here is that if you had another interface with an IP address 151.98.25.13/30 that you didnt want advertising updates the way to stop it is with the passive interface command.When you enable the passive-interface command for an interface it will still receive and process updates incoming on that interface,this interface in question will still be placed in the routing table and advertised to neighbours out all other interfaces which are included in the 151.98.0.0 range that do not have passive interface enabled.
Usually passive-interface is used in combination with the neighbour command,this is generally done on a broadcast network and gives you the possibity of unicasting your update to a particular neighbour rather than
broadcasting to all.
Another method of stopping updates is by using a distribute-list, the distribute-list is more powerful and can stop both incoming and outgoing updates.

rossonieri#1

ed_the_lad wrote:

Another method of stopping updates is by using a distribute-list, the distribute-list is more powerful and can stop both incoming and outgoing updates.

and maybe this is the answer to sputnic's question on CCNP's routing arch...
agree anyone ??

chinaman

Thanks It's more clear now. Sorry to disturb you guys, I'm really really want to get the CCNA cert. Hope I can pass actually I'm not more on networks I graduate from system software eng. but because I'm already bored in soft. eng I said to myself whynot try some other stuff so I was been encourage by my officemate who also wants to take CCNA.

Thanks for all help, this forum is very helpful.

regards,
chinaman

QUIX0TIC

Nice desriptions JohnnyND and Ed_the_Lad.

alexgne

Application of passive-interface depends on routing protocol under which is was set up. For example, for RIP, it'd stop sending the updates but will allow their receipt. Whereas for EIGRP, passibe-interface will neither send nor receive the updates. I am not sure how it works for IGRP and OSPF, I am still learning

chinaman

Oh I didn't know that. Thanks anyway I hope I can pass the exam.
Actually I have a 2 router simulator which is boson and sybex virtual lab.
I also have cisco ccna command ref. from cisco press and sybex but It's a 4th edition.

I'm planning to buy the cisco press bec. I feel that Sybex is not enough still there are some topic that are not explain well.

Hope guys you can help me to pass my ccna just give me some tips and some good idea where to focus.

Chinaman