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..
NSSA is similar to the OSPF stub area, but it has the capability to import AS external routes in a limited capacity within the NSSA area. NSSA allows importing type 7 LSAs within the NSSA area by redistribution and then converts them into type 5 at the ABR. This enables the administrator to summarize and filter data at both ASBR and ABR levels.
IP networks of the mid-1990s were invariably best-effort networks, and the Internet, as a whole, remains so today. Privately owned enterprise and service provider networks, though, have been widely transformed from best-effort models to more complex differentiated services models, meaning that the network gives different applications differing levels of service. Figure 1-1 shows the broad steps in the evolution of QoS concepts since the early 1990s. Figure 1-1. QoS Evolution..
v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} The standard Frame Relay header consists of two octets. Figure 1-4 illustrates the standard Frame Relay header. Figure 1-4. Standard Frame Relay Header The DLCI is a 10-bit address in the Frame Relay header, whose possible value ranges from 0 to 1023. The DLCI makes up the largest portion of the Frame Relay h..
