Less-Specific Routes of a Network's Own Aggregate

A specific rule of routing states that, for the sake of preventing routing loops, a network must not follow a less-specific route for a destination that matches one of its own aggregated routes. A routing loop occurs when traffic circles back and forth between network elements, never reaching its final destination. Default routes 0.0.0.0/0 are a special case of this rule. A network should not follow the default route to reach destinations that are part of its aggregated adver..

Using Multiple Authentication Methods

AAA authentication allows reference to multiple servers and to multiple authentication methods so that a user can be authenticated even if one authentication method is not working. The aaa authentication command supports up to four methods on a single command. Additionally, there is no practical limit to the number of RADIUS or TACACS+ servers that can be referenced in a RADIUS or TACACS+ server group. The logic used by Cisco IOS when using these methods is as follows: ■ U..

Network Fault Tolerance and MPLS OAM Mechanisms

Operation, administration, maintenance, and provisioning (OAM&P) encompass a broad set of management functional areas, including fault management, configuration management, accounting management, and security management.[20] A fault (or defect) is an interruption of the capability of a network connection caused by a network element such as link and node failures. Discussion of functions in this section is restricted to fault management and performance management: • ..

OSPF Router Types

When an OSPF network grows beyond a single area, you need to be aware of the role played by each OSPF router in a topology. Specifically, four OSPF router types exist: ■ Internal router: All the networks directly connected to an internal router belong to the same OSPF area. Therefore, an internal router has a single link-state database. ■ Area border router (ABR): An ABR connects to more than one OSPF area and therefore maintains multiple link-state databases (one for e..

PE-CE Communication via OSPF

You can use OSPF to exchange customer routing information between the CE and PE routers at each site. For this example, we will configure OSPF for the CE to PE IGP at Customer A's Sites 1 and 2, but not 3, so that we can show some of the idiosyncrasies of MP-BGP route redistribution. First we will configure the CE routers. We will use two OSPF network statements on the router at Site 1. The first, 192.168.1.0/24, allows this router to communicate with the PE router, while th..