notes: EIGRP Metric, Timers and K-values

EIGRP uses a composite metric such as Interior Gateway Routing Protocol (IGRP), but it is modified with a multiplier of 256. Bandwidth and delay are the defaults enabled. EIGRP calls the metric feasible distance.

- EIGRP calculates all metrics from outgoing interfaces only.
- The composite metric is minimum bandwidth of an outgoing interface, cumulative delay, load, and reliability.
and smallest MTU along a path.

- Metrics:

1. BW - Expressed in units of kilobits per second.
- Static number used for metric calculation only, doesn’t reflect actual bandwidth.
- To calculate EIGRP bandwidth metric amount: 10 000 000/configured BW.
- Expressed in kilobytes; to adjust the bandwidth value assigned to an interface, use the bandwidth command.

2. DLY - Static figure, expressed in units of microseconds.
- To calculate EIGRP DLY metric amount : DLY/10.

3. REL - Dynamically measured.
- Is expressed as an eight-bit number, where 255=100% reliable link and 1= minimally reliable link.
- Expressed in microseconds; it can be adjusted using the delay command; when manipulating metrics, consider delay because bandwidth would affect other protocols, too.

4. LOAD - Dynamically measured.
- Is expressed as an eight-bit number, 1=minimally loaded link, and 255=100% loaded link.

5. MTU - Maximum transmission unit; the smallest recorded MTU in the path. Note that MTU is not used in metric calculation.

- Default K-Values: K1=1 K2=0 K3=1 K4=0 K5=0
- EIGRP Metric =

256*((K1*Bw) + (K2*Bw)/(256-Load) + (K3*Delay)*(K5/(Reliability + K4)))

- By default, EIGRP chooses a route based ONLY on bandwidth and delay. (Due the default k-values)

> Default metric = 256 x [10^7 / (min(BW)) + (sum(DLY)) / 10]

- EIGRP supports hop-count merely as a way to prevent routing loops.


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COMMANDS
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1. Changes the default hop-count limit of 100. Values 1-225

metric maximum-hops {number}

2. Changes the metric calculation of the K-values (K1=1 K2=0 K3=1 K4=0 K5=0)

metric weights tos k1 k2 k3 k4 k5

3. Changes the metric calculation to only use DLY

metric weights 0 0 0 1 0 0

4. Changes the metric calculation to only use BW

metric weights 0 1 0 0 0 0

5. Changes the bandwidth to 64 Kbit, and Specifies delay in tens of microseconds, changes the delay to 50 usec.

interface e0
bandwidth 64
delay 5

timers

1. hello

interface
ip hello-interval eigrp [as#] [time-seconds]


2. hold time

interface
ip hold-time eigrp as# [as#] [time-seconds]

3. nsf-hello timer

router eigrp 100
timers nsf route-hold [time-seconds]

4. active timer - SIA

router eigrp 100
timers active-time