FirstDigest » Cisco-IGP

OSPF: Area range vs Summary address

Calin — Sat, 06 Mar 2010 00:04:41 +0000

It seems like an easy one! I mean what could be so hard about area range and summary address command? You will be surprised how many people tend to forget this things or to apply them when not necessary or even worst where is their place to be added. It’s basic knowledge, but sometimes exactly this basic knowledge give us headache.

In the following line, I will try to explain briefly the difference between Area range and Summary address command. First let’s have a look [...]

Cisco: Deny false information routing injection into OSPF domain

Calin — Mon, 17 Nov 2008 20:45:36 +0000

In a well controlled environment, false information routing should not reach your OSPF domain, as network engineer take care what to advertise and what not into OSPF. But there are cases when you have to deal with 3rd party companies somehow, and you want to be sure that nothing in injected by mistake into your domain. Also this can be a task for CCIE RS lab exam.

And since I specified that this can be an exam task, let take some “DO NOT USE” rule [...]

How to force Loopack interface to be advertised with a /24 netmask

Calin — Tue, 11 Nov 2008 22:42:35 +0000

Many of you already know that usually when you advertise a Loopback interface into OSPF it is advertised with /32 netmask (one IP address) even if the IP address under Loopback interface is with a /24 netmask. If you checked my previous post, you’ll see at the end that I’m right, and the Lo0 address is advertised with /32 netmask.

But what if you have to advertised as a /24 subnet (task require or some testing) ? There is “dirty little trick” to do it. [...]

How to advertise subnet into OSPF without network or redistribution command

Calin — Tue, 11 Nov 2008 21:49:02 +0000

During my CCIE R&S preparation for lab exam, I encounter a task that requested me to advertise a subnet into OSPF routing protocol, but without using network statement or redistribution command. Since back then I was a little confuse about this, I said to post here maybe it help others.

Please download the topology used in this example here. We have already OSPF prepared and the task request to advertise interface Loopack0 from R0 to OSPF without using network statement or [...]