Jan 3 2009

ISIS level-1, level-2 areas, ISIS redistribution and ISIS default route origination.

I’m going to cover following three things in this post.

1. Level-1, Level-1-2 and Level-2-only routers.  How to configure and what is the att bit
2. Investigate the default behavior of the various levels with respect to routing updates.  ie are level-2 prefixes by default advertised to level-1 routers.
3. Finally we will cover how to originate a default route within a level-2 area.

Consider the topology below.

Some important points worth noting:

1. level-1-2 router HAVE to be in the same area as level-1 routers otherwise level-1 routers will not be able to form an adjacency with them.
2. the level-1-2 router must have a level-2 adjacency with a router in another area for the att bit to be set in outgoing level-1 updates.
3. By default level-1 routes are advertised to level-2 routers.
4. By default level-2 routes are NOT advertised to level-1 routers.

Watch the video below or alternatively download the video and watch it on your iPod .

The command used for the above configuration are:

R1

frame-relay switching
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Serial1/0
ip address 10.0.0.1 255.255.255.252
ip router isis
encapsulation frame-relay
clockrate 128000
no arp frame-relay
frame-relay map clns 200 broadcast
frame-relay map ip 10.0.0.2 200
no frame-relay inverse-arp
frame-relay intf-type dce
!
router isis
net 49.0001.0000.0000.0001.00
is-type level-1
passive-interface Loopback0
!

R2
!
frame-relay switching
!
interface Serial1/0
ip address 10.0.0.5 255.255.255.252
ip router isis
encapsulation frame-relay
no fair-queue
serial restart-delay 0
clockrate 128000
no arp frame-relay
frame-relay map ip 10.0.0.6 200
frame-relay map clns 200 broadcast
no frame-relay inverse-arp
frame-relay intf-type dce
isis circuit-type level-2-only
!
interface Serial1/1
ip address 10.0.0.2 255.255.255.252
ip router isis
encapsulation frame-relay
no arp frame-relay
frame-relay map clns 200 broadcast
frame-relay map ip 10.0.0.1 200
no frame-relay inverse-arp
isis circuit-type level-1
!
router isis
net 49.0001.0000.0000.0002.00
redistribute isis ip level-2 into level-1 distribute-list 100
!
access-list 100 permit ip any any

R3

interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface Serial1/0
ip address 10.0.0.6 255.255.255.252
ip router isis
encapsulation frame-relay
serial restart-delay 0
no arp frame-relay
frame-relay map clns 200 broadcast
frame-relay map ip 10.0.0.5 200
no frame-relay inverse-arp
!
router isis
net 49.0002.0000.0000.0003.00
is-type level-2-only
passive-interface Loopback0
default-information originate

By zismail • CCIE SP, Inter-AS, iPod, IS-IS • 1 • Tags: CCIE SP, IS-IS