Help on LMI's

ifonlyunu

I am attempting to take the CCNA exam in a couple of weeks and I keep running in to different information. For example, are LMI's sent every 60 seconds or every 10 seconds? I am currently using Todd's Deluxe Edition 4th V. Todd says every 60, but my practice exams are saying every 10 seconds. Also, Todd's book seems to lack in regard to switch port security explanation/configuration and ip subnet zero explanation/configuration. I have cross referenced my studies with an older CISCO press book, "Cisco CCNA EXAM #604-607" by Wendell Odom... this has been very helpful, but I need more current study material. Moreover, could somebody direct me to a great source concerning ip subnet zero and switch port security configuration.

Thanks! :

Drakonblayde

ip subnet zero ain't hard. While you were learning how to subnet, you were probably told that you can't use the first or the last subnet. ip subnet zero allows you to use the very first subnet. configuration is as simple as entering it's command (indeed, it's on by default in newer IOS releases).

That really is all there is to it. In order to understand what subnet zero does, you have to have a solid foundation in subnetting.

kplab

The following papers explain the details about port security configuration:

Configuring Port Security (by Cisco):
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12122ea2/2950scg/swtrafc.htm#wp1038501

Fundamentals of Switching (by KP-LAB):
http://www.kp-lab.com/download.htm

tunerX

Your tests and the book are both right. The LMI functions with two different intervals. The router sends an LMI inquiry message and the switch responds with a status.

Every 10 seconds the router will send an LMI request about all of its DLCIs. The frame switch responds with the status of those DLCIs.

Every 60 seonds the router will send a full LMI request. This message is designed to get a complete update of all PVCs on a link. It will also discover new DLCIs.

The 10 second interval is used to make sure that a single, already known, PVC is still good. The 60 second interval makes sure that all discovered PVC's are active and will also discover new PVCs.

Once a PVC is known and no others will be added then the 60 second full LMI message is un-important. The 10 second LMI is used as a keepalive to ensure that each DLCI is good and running.

You can do a "debug frame-realy lmi" and see the different messages being sent and recieved.