| 1: | Name the three network layer protocols that form the basis of ISO connectionless network services. |
| A1: | CLNP, ES-IS, and IS-IS. |
| 2: | How many levels are there in the routing hierarchy supported by the IS-IS routing protocol? |
| A2: | ISO 10589 specifies two levels: Level 1 and Level 2. |
| 3: | What is the general layout of the IS-IS packet format? |
| A3: | All IS-IS packets consist of a header to which special routing information fields, known as TLVs, are appended. |
| 4: | What does the acronym NSAP stand for, and what is it used for? |
| A4: | NSAP stands for network service access point. NSAPs are network layer address OSI nodes running the CLNP protocol. |
| 5: | What are the three major components of an NSAP? Describe the significance of each. |
| A5: | The three components are area ID, system ID, and N -selector. The area ID defines the area that the node belongs to, the system ID is a unique address of the node within its area, and the N -selector specifies a network service user . A 0 value specifies the routing layer. |
| 6: | What is the maximum length of an NSAP, and what is the minimum length that can be configured on a Cisco router? |
| A6: | The maximum length of an NSAP is 160 bits, or 20 bytes. The minimum size that can be configured on a Cisco router is 8 bytes. The 8 bytes include 1 byte of N -selector, 6 bytes of system ID, and 1 byte of area ID. |
| 7: | What is the significance of the IS-IS link-state database? |
| A7: | Link-state protocols such as IS-IS require each router in an area to have the same view of the area's topology. Each router creates a link-state packet that describes its immediate environment shared with other routers in the area. LSPs are collected in the link-state database. When pieced together, the LSPs in an area's link-state database describe the topology of the entire area. |
| 8: | What is the basic difference between Level 1 and Level 2 link-state databases? |
| A8: | A Level 1 link-state database describes a single IS-IS area and contains only LSPs from the routers in that area. The Level 2 database describes the interconnection between areas in the IS-IS domain and contains LSPs from the Level 2 routers. The Level 2 LSPs are intended to provide interarea information. |
| 9: | How are flooding and database synchronization different between a point-to-point link and a broadcast link? |
| A9: | LSPs are flooded reliably with acknowledgments on point-to-point links, whereas they are not acknowledged on broadcast links. Database synchron- ization occurs on broadcast media through the designated router, which sends periodic CSNPs over the link to assist with synchronization. |
| 10: | Describe the two steps for enabling basic IS-IS routing on a Cisco router. |
| A10: | First, an IS-IS routing process is configured with the router isis [ tag ] command. Then, IS-IS routing is enabled on the relevant interfaces with the ip router isis [ tag ] interface-level command. |
| 11: | List some show commands that you can use to verify configuration and operation of IS-IS. |
| A11: | show clns neighbors, show clns interface, show isis topology, and show is-is database. |
