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- The only limitation of EIGRP is that it is Cisco-proprietary, which means it cannot be
implemented in environments with routers from various vendors. Anyway, a possible solution is
route redistribution, where a router exchanges routes between 2 routing protocols.
- EIGRP is suitable for very large networks. These networks are normally divided into multiple
EIGRP autonomous systems (ASs). Route information can be shared among different ASs via
redistribution. Internal EIGRP routes (AD = 90), are routes that originated by EIGRP routers
within an AS. Another type of routes – external EIGRP routes (AD = 170), are routes that
originated from another EIGRP AS, or redistributed from another routing protocol, eg: OSPF.
Note: The maximum hop count for EIGRP (and IGRP) is 255, with the default value 100. The
metric maximum-hops {hop-count} router subcommand can be used to change this value.
- IGRP, OSPF, and EIGRP features comparison chart:
Feature IGRP OSPF EIGRP
Discover neighbors before exchanging routing information No Yes Yes
Build some form of topology table besides the routing table No Yes Yes
Converge quickly No Yes Yes
Calculate metric based on bandwidth and delay (by default) Yes No. Cost Yes
Send full routing information on every routing update cycle Yes No No
Implement distance-vector loop-avoidance features Yes No No
Public standard No Yes No
- RIPv2, OSPF, and EIGRP support variable length subnet mask and discontiguous networks.
When selecting the suitable routing protocol to be implemented on a network environment, the
simplest routing protocol that meets the requirements should be selected.
Type of Network Suitable Routing Protocol
- No redundant links or parallel paths.
RIPv1
- Not requires VLSM or discontiguous subnets.
- Has redundant links or parallel paths.
- Not requires VLSM or discontiguous subnets.
- No redundant links or parallel paths.
- Requires VLSM and/or support of discontiguous subnets.
- Has redundant links or parallel paths.
- Requires VLSM and/or support of discontiguous subnets.
97
IGRP
RIPv2
OSPF or EIGRP
- Discontiguous networks are networks that have subnets of a major network separated by a
different major network. Figure 13-3A shows a typical discontiguous network where subnets
172.16.10.0 and 172.16.20.0 are connected together with (or separated by) a 10.1.1.0 network.
Discontiguous networks won’t ever work with RIPv1 and IGRP; and they don’t work by default
with RIPv2 and EIGRP as well, as they perform autosummarization by default.
172.16.10.0/24 172.16.20.0/24
10.1.1.0/24
172.16.10.0/24 172.16.20.0/24
172.17.10.0/24
Figure 13-3: Sample Discontiguous Networks
192.168.1.0/26 192.168.1.64/26
192.168.2.0/24
Figure 13-3A Figure 13-3B Figure 13-3C
Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com