Physical Versus Logical Connections

External BGP neighbors have a restriction in that they must be physically connected, adjacent to one another. BGP drops any UPDATE message from its external BGP peer if the peer is not physically connected, unless otherwise specified. However, some situations arise in which external neighbors cannot be on the same physical segment. Such neighbors are logically connected (multiple IP hops away) but not physically connected. An example would be running BGP between external neig..

Neighborship and Reliable Incremental Updates

EIGRP produces reliable updates by identifying its packets using IP protocol 88. Reliable, in a networking context, means that the receiver acknowledges that the transmission was received and understood. EIGRP only repeats itself if an advertisement is lost, so EIGRP is less "chatty" than other protocols. EIGRP uses the following five types of packets to communicate. These packets are directly encapsulated by IP. • Hello— Identifies neighbors. Hellos are sent as periodi..

Role of Identity in Secure Networking

Although there are clearly right and wrong ways to deploy security technologies, identity is less obvious. From a network designer's perspective, you must start by deciding where and what kind of identity information you must acquire. Broadly defined, there are three potential network identity paths: 1.    Device to network A device authenticates to the network or another device within the network. 2.    User to network A user authenticates to t..

Monitoring and Troubleshooting Multilink Frame Relay

This section discusses the various show commands for monitoring and maintaining Multilink Frame Relay on a Cisco router. The end of this section looks at the IOS debug commands available for troubleshooting Multilink Frame Relay. The network diagram portrayed in Figure 14-1 and the base configurations shown in Example 14-1 are used for this discussion. Example 14-6 shows the output of the show interface mfr [mfr_number] command. This is executed on router R1 after the bundle..

Preventing Unwanted Neighbors Using Passive

Interfaces When an EIGRP network configuration subcommand matches an interface, EIGRP on that router does two things: Step 1. Attempts to find potential EIGRP neighbors by sending Hellos to the 224.0.0.10 multicast address Step 2. Advertises about the subnet connected to that interface In some cases, however, no legitimate EIGRP neighbors may exist off an interface. For example, consider the small internetwork of Figure 1-1, with three routers, and with only one router connec..