CISCO ENHANCED INTERIOR GATEWAY ROUTING PROTOCOL (EIGRP)
EIGRP Metric Calculation
The routes in an EIGRP Topology Table contain metric detail, which indicates how long this is from a particular destination network. But how does the estimation work? EIGRP is a little more interested than RIP or OSPF in its metric computation. In fact, the metric of EIGRP is a bandwidth-based and delaying integer, by necessity. However, other elements can be used for the metric calculation. Take the metric formula of EIGRP:
Note the metric calculation is a series of K-values, consisting of zero or any positive integer that can be configured. Bandwidth, delay, load and reliability are all included in the measurement. Of special note, many of the EIGRP literature claim that the metric is also based on the maximum transmission unit (MTU) of the interface. Now see the figure below as example to solve the EIGRP Metric Calculation,
hostname R1
int e0/0
ip addr 172.16.12.1 255.255.255.0
no shutdown
router eigrp 1
network 172.16.12.0
auto-summary
do show ip eigrp topology
router eigrp 1
metric weights 0 5 2 1 10 1
hostname R2
int e0/0
ip addr 172.16.12.2 255.255.255.0
no shutdown
int e0/1
ip addr 172.16.23.2 255.255.255.0
no shutdown
router eigrp 1
network 172.16.12.0
network 172.16.23.0
auto-summary
do show ip eigrp topology
do sh int e0/0 | include BW
hostname R3
int e0/0
ip addr 172.16.23.3 255.255.255.0
no shutdown
router eigrp 1
network 172.16.23.0
auto-summary
int lo 0
ip addr 172.16.34.3 255.255.255.0
no shutdown
do show ip eigrp 1 topology
do sh int l0 | include BW
EIGRP - Summarization
One of the benefits of EIGRP in contrast with certain other routing protocols (e.g. OSPF) is the ability to manually summarize any network router. A single route can serve multiple routes that minimize the size of network routing tables. The manual description is per-interface setup. The command's syntax is:
(config-if) ip summary-address eigrp ASN SUMMARY_ADDRESS SUBNET_MASK
Now based on picture above, lets' practice by the following command below,
hostname R1
int e0/0
ip addr 172.16.13.1 255.255.255.0
no shutdown
router eigrp 1
network 172.16.13.0 0.0.0.255
auto-summary
do ping 172.16.34.4
hostname R2
int e0/0
ip addr 172.16.23.2 255.255.255.0
no shutdown
router eigrp 1
network 172.16.23.0 0.0.0.255
auto-summary
hostname R3
int e0/0
ip addr 172.16.13.3 255.255.255.0
no shutdown
int e0/1
ip addr 172.16.23.3 255.255.255.0
no shutdown
int e0/2
ip addr 172.16.34.3 255.255.255.0
no shutdown
router eigrp 1
network 172.16.13.0 0.0.0.255
network 172.16.23.0 0.0.0.255
network 172.16.34.0
auto-summary
do sh ip ro | begin Gateway
int e0/2
ip summary-address eigrp 1 172.16.0.0 255.255.224.0
do sh ip ro | begin Gateway
no ip summary-address eigrp 1 172.16.0.0 255.255.224.0
router eigrp 1
auto-summary
do sh ip ro | begin Gateway
router eigrp 1
summary-metric 172.16.0.0 255.255.224.0 100 100 1 1 1 distance 50
hostname R4
int e0/0
ip addr 172.16.34.4 255.255.255.0
no shutdown
router eigrp 1
network 172.16.34.0
no auto-summary
do sh ip ro
do sh ip ro | begin Gateway