CCNP Tutorial For The BSCI Exam

Configuring ISIS Over Ethernet And Changing Route Types

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The July 2010 CCNP Changes (And How To Beat Them!)

Previously in our ISIS configuration tutorial series, we looked at quite a bit of ISIS theory and then configured ISIS over Frame Relay.

We'll now add a few routers and some Ethernet segments to our network. If you're just joining us at this point, you may want to take a look at that ISIS/Frame Relay tutorial to see what configurations have already been, well, configured!

R7 will now be brought into Area 49.0005, and R8 into Area 49.0004.

First we'll configure R5 and R7. We configured the NET on R5 in the Frame Relay portion of this lab, so we only need the ip router isis command on R5's ethernet interface (Fast Ethernet, to be precise):

R5(config)#int fast 0/0
R5(config-if)#ip router isis

We'll configure a NET on R7 along with the ip router isis command.

R7(config)#router isis
R7(config-router)#net 49.0005.7777.7777.7777.00
R7(config-router)#interface fast 0/0
R7(config-if)#ip router isis

Of course, we'll verify the neighbor relationship!

R7#show clns neighbor

System Id      Interface     SNPA                State  Holdtime  Type    Protocol
R5                 Fa0/0       000a.4164.70c1      Up     28          L1L2     IS-IS

We'll now add the appropriate commands to R4 and R8, and then check the adjacencies on R4. We should see three of them by that point.

R8(config)#router isis
R8(config-router)#net 49.0004.0008.0008.0008.00
R8(config-router)#interface fast 0/0
R8(config-if)#ip router isis

R4(config)#int fast 0/0
R4(config-if)#ip router isis

R4#show clns neighbor

System Id      Interface   SNPA                   State  Holdtime  Type   Protocol
R8                   Fa0/0       0006.53fe.a0c0    Up     27          L1L2    IS-IS
R2                   Se0/0       DLCI 401                Up     27           L2      IS-IS
R5                   Se0/0       DLCI 405                Up     7             L2      IS-IS

We have three adjacencies on R4, but the SNPA is quite different on the most recent.

Also note the different kinds of adjacency types shown. Those are important differences, so let's take a detailed look at why those values are what they are - and why and how to change them.

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Here's that adjacency table again:

R4#show clns neighbor

System Id      Interface   SNPA                   State  Holdtime  Type   Protocol
R8                   Fa0/0       0006.53fe.a0c0       Up     27          L1L2    IS-IS
R2                   Se0/0       DLCI 401                Up     27           L2      IS-IS
R5                   Se0/0       DLCI 405                Up     7             L2      IS-IS

Note the SNPA value for R8 is R8's MAC address for its Fast Ethernet 0/0 interface.  The adjacency with R8 has defaulted to an L1/L2 setting.  In this network topology, there is no reason for R7 or R8 to be anything but an L1 router, since they each have only one path to the other area. 

The ISIS adjacency type is changed under the protocol process with the is-type command (this changes all links on the router to the desired type), or at the interface level with the isis circuit-type command. 

To get some practice with each command, we'll use the is-type command on R7 and the isis circuit-type command on R8's FE 0/0 interface.

R7(config)#router isis
R7(config-router)#is-type level-1 (configured at router protocol level)

R7#show clns neighbor

System Id      Interface         SNPA                State     Holdtime    Type    Protocol
R5                  Fa0/0       000a.4164.70c1      Up           27             L1        IS-IS

R8(config)#int fast 0/0
R8(config-if)#isis circuit-type level-1 (configured at interface level)

R8#show clns neighbor

System Id      Interface          SNPA                State    Holdtime     Type    Protocol
R4                   Fa0/0       000c.31ef.9c60        Up             8             L1         IS-IS

Both R7 and R8 now have level-1 adjacencies with R5 and R4, respectively.  Let's take a look at R8's routing table.

R8#show ip route isis
     172.12.0.0/24 is subnetted, 1 subnets
i L1    172.12.123.0 [115/20] via 46.1.1.4, FastEthernet0/0
i*L1 0.0.0.0/0 [115/10] via 46.1.1.4, FastEthernet0/0

R8 has a specific route to 172.12.123.0, and a default route (remember what that asterisk means!). 

Both routes are L1 routes, which is what we would expect after configuring the L4-L8 link as a type-1 link.  Note the AD of ISIS is 115, and the default route metric is 10. 

The segment connection R5 and R7 is 51.1.1.0 /24, located in Area 49.0005. Can R8 ping those routers on that segment via that default route?

R8#ping 51.1.1.5

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 51.1.1.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 64/64/68 ms

R8#ping 51.1.1.7

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 51.1.1.7, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 64/65/69 ms

Sure can!

Let's take a look at the ISIS routing tables on the other routers.

R4's ISIS table has only one route, the route to 51.1.1.0 /24. It is marked as an L2 route, since it is a route to a network in another area.

R4#show ip route isis
     51.0.0.0/24 is subnetted, 1 subnets
i L2    51.1.1.0 [115/20] via 172.12.123.5, Serial0/0

R5's ISIS table is similar, except the L2 route it contains is 46.1.1.0 /24, the link between R4 and R8.

R5#show ip route isis
     46.0.0.0/24 is subnetted, 1 subnets
i L2    46.1.1.0 [115/20] via 172.12.123.4, Serial0/1

R7's ISIS table (not shown) has much the same table as R8 does, and has connectivity to the IP addresses on the 46.1.1.0 /24 subnet via its default route.

R7#ping 46.1.1.4

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 46.1.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 64/65/68 ms

R7#ping 46.1.1.8

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 46.1.1.8, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 64/65/68 ms

Before moving on to a route summarization tutorial with ISIS, let's talk about the metrics. 

Cisco only supports one ISIS metric, default, which is commonly referred to as cost. 

The default for this metric on a Cisco interface is 10. 

Other ISIS metrics are delay, expense, and error.  Cisco routers do not support these three metrics.

Whew! Catch your breath and then we'll head into a discussion of configuring route summarization with ISIS. I'll post that on our CCNP BSCI Tutorial along with the other ISIS tutorials already there!

Chris Bryant

CCIE #12999

"The Computer Certification Bulldog"

chris@thebryantadvantage.com