Information Technology Reference
In-Depth Information
Acknowledgment:
An acknowledgment packet acknowledges the receipt of an up-
date packet. It is a hello packet with no data. EIGRP sends acknowledgment packets
to the unicast address of the sender of the update packet.
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Update:
Update packets contain routing information for destinations. EIGRP uni-
casts update packets to newly discovered neighbors; otherwise, it multicasts update
packets to 224.0.0.10 when a link or metric changes. Update packets are acknowl-
edged to ensure reliable transmission.
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Query:
EIGRP sends query packets to find feasible successors to a destination.
Query packets are always multicast unless they are sent as a response; then they are
unicast back to the originator.
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Reply:
EIGRP sends reply packets to respond to query packets. Reply packets pro-
vide a feasible successor to the sender of the query. Reply packets are unicast to the
sender of the query packet.
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EIGRP Design
When designing a network with EIGRP, remember that it supports VLSMs and network
summarization. EIGRP allows for the summarization of routes in a hierarchical network.
EIGRP is not limited to 16 hops as RIP is; therefore, the network diameter can exceed this
limit. In fact, the EIGRP diameter can be 225 hops. The default diameter is 100. EIGRP
can be used in the site-to-site WAN and IPsec virtual private networks (VPN). In the en-
terprise campus, EIGRP can be used in data centers, server distribution, building distribu-
tion, and the network core.
EIGRP does not broadcast its routing table periodically, so there is no large network over-
head. You can use EIGRP for large networks; it is a potential routing protocol for the core
of a large network. EIGRP further provides for route authentication.
As shown in Figure 10-12, when you use EIGRP, all segments can have different subnet
masks.
Router A
Router B
172.16.3.4/30
172.16.2.64.0/26
172.16.1.0/24
Figure 10-12
EIGRP Design
EIGRP is suited for almost all enterprise environments, included LANs and WA N s and is
simple to design. The only caveat is that it is a Cisco proprietary routing protocol which can-
not be used with other vendors. The use of EIGRP is preferred over RIP in all environments.
