Cisco IOS switches have two levels of access by default: User (Level 1) and Privileged (Level 15). The User level is typically accessed via Telnet or SSH connections to a switch or via the console line on the switch. The Privileged level is typically accessed after the User level is established. Each level is usually configured with a password. The Privileged level can be configured with either an “enable” password or an “enable secret” password. The “enable secret..
RIP offset lists allow RIP to add to a route’s metric, either before sending an update, or for routes received in an update. The offset list refers to an ACL (standard, extended, or named) to match the routes; any matched routes have the specified offset, or extra metric, added to their metrics. Any routes not matched by the offset list are unchanged. The offset list also specifies which routing updates to examine by referring to a direction (in or out) and, optionally, an ..
OSPF creates a two-level hierarchy of areas. Area zero (also called the backbone area or transit area) is always the central area; all other areas attach to area zero. Area zero forms the top level in the hierarchy and the remaining areas form the bottom level of the hierarchy. This hierarchical design supports summarization and minimizes routing table entries. Routers in area zero are called backbone routers. Routers that link area zero and another area are cal..
Figure 4-3 shows the IGRP packet format. In this figure, you can see that IGRP updates provide more information than RIP and, at the same time, are more efficient. None of the fields in an IGRP packet is left unused; after the 12-octet header, each routing entry is filled one after another. Therefore, IGRP does not pad the update packet to force a 32-bit word boundary. With this efficient design, IGRP can carry a maximum of 104 fourteen-octet entries. Therefore, with its MTU ..
The static routes that we discussed in the previous section all had relatively low administrative distance values. If the router has two routes to the same destination but with different distances, it will always choose the one with the lower distance value. This concept also includes the routes that come from other sources, such as dynamic routing protocols. Every routing protocol has an administrative distance that indicates how much the router trusts the information it rec..
