Before you can modify port settings, you must select one or more switch ports. Even though they have traditionally been called ports, Catalyst switches running the Cisco IOS Software refer to them as interfaces. To select a single switch port, enter the following command in global configuration mode: Switch(config)# interface type module/number The port is identified by its Ethernet type (fastethernet, gigabitethernet, tengigabitethernet, or vlan), the physical ..
EIGRP Basics and Steady-State Operatio
Many CCIE candidates have known, at least at some point, many of the details of EIGRP operation and configuration. EIGRP is widely deployed and is thoroughly covered on the CCNP BSCI exam. With that in mind, this chapter strives to review the key terms and concepts briefly, and get right to specific examples that detail EIGRP operation on a Cisco router. To that end, the chapter begins with Table 9-2, which lists some of the key features related to EIGRP. Table 9-2 EIGRP Fea..
The Diffusing Update Algorithm
The Diffusing Update Algorithm (DUAL) is the brain behind the operation of EIGRP. It is an algorithm that tracks all the routes advertised from a neighbor and then selects a loop-free path to the destination. Before discussing the details of DUAL, you must understand several terms and concepts: • Feasible distance (FD)— Feasible distance is the minimum metric along the path to a destination. Figure 6-1 shows the feasible distance calculation to reach Network 7 for e..
Understanding the IS-IS Area Concepts
Routers with common area IDs belong to the same area. By the nature of its addressing system, IS-IS forces this hierarchy. IS-IS has two layers of hierarchy: level 1 and level 2 (backbone). The backbone must be contiguous. In IS -IS, the area border is on the links instead of the router. Routers that connect multiple areas maintain two separate link-state databases: one for level 1 areas, and the other for level 2 areas. The routers also run two separate SPF algorithms. ..
Comparison of the IS-IS Restart Mechanisms
The advantages of the IETF IS-IS restart approach include scalability (does not require IS-ISrelated state preservation across the restart) and standards-based implementation. Disadvantages of this approach are that it requires IS-IS protocol extensions and support from its neighbors (helper nodes). To elaborate on this further, consider a router R1 in a provider's network that is peering with an R2 that might be managed by another provider or a customer. The IETF IS-IS resta..
