Administering Cisco QoS for IP Networks
Tweak and tune your Cisco routers for best performance with this practical guide.
TABLE OF CONTENTS Administering Cisco QoS for IP Networks
Defining the Four Basic Components of EIGRP
Before we can begin an in-depth discovery of EIGRP, we need to define the four basic components that define what EIGRP is and how it functions.
Establishing Protocol-Dependent Modules
EIGRP has been designed for implementation in IP, IPX, and AppleTalk environments. EIGRP uses protocol-dependent modules that are responsible for establishing and maintaining protocol-specific routing information. IPX and AppleTalk are outside of the scope of this book.
EIGRP was designed to coexist with legacy IP, IPX, and AppleTalk networks to allow an easy path of migration to EIGRP. EIGRP will automatically redistribute with legacy protocols in the following manner:
- IP EIGRP automatically redistributes with IGRP if they are configured with the same Autonomous System number.
- IPX EIGRP automatically redistributes with IPX RIP and NLSP.
- AppleTalk EIGRP automatically redistributes with RTMP.
With these redistribution capabilities, it becomes much easier to migrate your network segment by segment to EIGRP, or to interconnect a legacy network to a newer EIGRP network.
Establishing Neighbor Discovery/Recovery
Unlike other distance-vector protocols, EIGRP routers establish and maintain adjacencies with directly connected neighbors through a process of Neighbor Discovery/Recovery. Periodically, small hello packets are multicast identifying themselves to their neighbors to form the adjacencies. Only after the adjacency is established will the routers exchange routing information. Moreover, since EIGRP does not broadcast periodic updates, hello packets are also used to determine if a neighbor (and, therefore, any route through that neighbor) is still active.
The Hello Protocol...
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