In the exhibit, how many Level 1 adjacencies does Montreal have?

Refer to the Exhibit.

In the exhibit, how many Level 1 adjacencies does Montreal have?

A.
2

B.
3

C.
4

D.
5

Explanation:
Troubleshooting Integrated IS-IS

The basic methods for troubleshooting IS-IS are very similar to the methods for troubleshooting OSPF, A major aspect of troubleshooting Integrated IS-IS that is different from the other IP routing protocols is that IS-IS uses CLNS PDUs rather than IP packets. If you are troubleshooting the protocol itself, remember that you are troubleshooting CLNS, not IP.

As with all routing protocols, the first troubleshooting step is to check the route table for accurate information. If an expected route entry is missing or incorrect, the remainder of the troubleshooting task is to determine the source of the problem.

After the route table, the link-state database is the most important source of troubleshooting information. As recommended in Chapter 8, it is good practice to keep a copy of the L1 link-state database for every area, and a copy of the L2 link-state database. These stored copies of the databases should be updated regularly, as part of your routine baselining procedures. When things go wrong, these stored databases provide a steady-state reference.

When examining an individual router’s configuration, consider the following:

* Does the net statement under the IS-IS configuration specify the correct NET? Are the Area ID and System ID correct for this router? Does the NET comply with whatever CLNS addressing convention is being used in this network?
* Is IS-IS enabled on the correct interfaces with the ip router isis or ipv6 router isis command?
* Are the IP addresses and subnet masks or prefixes correct? It is doubly important to check these in an Integrated IS-IS environment because a misconfigured IP address will not prevent an IS-IS adjacency from being partially established.
*
Troubleshooting IS-IS Adjacencies

The command show clns is-neighbors displays the IS-IS neighbor table. The entire table is displayed by default, or you can specify a particular interface. From this table, you can observe whether all expected neighbors are present and whether they are the correct type. For more information, such as the area addresses and IP addresses associated with each neighbor and the uptime of each neighbor, use the show clns is-neighbors detail command.

When examining adjacencies, consider the following:

* Are the router levels configured correctly? L1 routers can establish adjacencies only with L1 and L1/L2 routers, and L2 routers can establish adjacencies only with L2 and L1/L2 routers.
* Are Hellos being sent from both neighbors? Are the Hellos the correct level, and do they contain the correct parameters? The command debug isis adj-packets is useful for observing Hellos.
* If authentication is being used, are the passwords and authentication mode the same between neighbors? Remember that area (level 1) and domain (level 2) authentication do not regulate adjacencies, only the exchange of LSPs.
* Are any access lists blocking IS-IS or CLNS?