Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 

Using area <> filter-llist command in ospf

 

 

 

Introduction

 

This document provides a sample configuration on how to use area <> filter-list command. This feature was introduced in IOS release 12.0(15)S and is used for filtering LSA type 3 only. This filter can be used to filter type 3 LSA coming into an area, going out of an area or both.

 

Requirements

 

It is assumed that a person reading this document is familiar with Ospf.

 

Components used

 

For this document 3700 Series router with IOS 12.4(18) loaded in it.

 

Network Diagram

 

Area filter- ospf.jpg

Configuration

 

The configuration files are attached with this document.

 

For this example we will take network attached to loopback 1 (11.1.1.0/24) and filter that out in a way that routers in Area 1 don't see it.

 

Before we start applying filters lets take a look at routing table of R2 and R3:

 

From Router R2:

 

R2.jpg

 

And, we can surely see network 11.1.1.0. Now, to make sure that we have it on Router R3 as well, lets have a look at its routng table:

 

 

R3.jpg

and, its there as well.

 

Now for filtering network 11.1.1.0 from area 1 we need to perform two tasks

 

  • We first need to configure a prefix-list which will filter this particular network out.
  • Second, we need to apply that filter

 

This will be done at router R2, which is the ABR for Area 1.

 

For step 1, we will create a prefix-list which will filter net 11.1.1.0/24 and permit all others:

 

prefix-list.jpg

 

For step 2, we will apply this filter:

 

apply filter.jpg

We can also apply the same filter in out direction but then we would have to do it on Area 0 as this is the area from which this network is advertised out.

Verify

 

Lets see the routing table of Router R3:

 

R3 after filter.jpg

 

We surely don't see 11.1.1.0 network on R3. And, to prove that R2 is not sending type 3 LSA for this network in area 1, lets see the database for 11.1.1.0 network on R2:

 

 

R2 after filter.jpg

Related Information

4196
Views
0
Helpful
0
Comments