I like the way Jeff Doyle writes this IGRP & EIGRP metric formulas.
It looks to me that all other ways just confuse people. At least
that is my opinion, which don't have to be true. For example,
Priscilla wrote:
> The metric = [K1 * bandwidth + (K2 * bandwidth) / (256 - load) + K3 *
> delay] * [K5 / (reliability + K4)]
but if someone try to calculate EIGRP metric based on above formula,
with specified minimum bandwidth and total delay, as reported with
show ip eigrp topology a.b.c.d
he/she won't get the correct result, because bandwidth and delay in
above formula aren't bandwidth and delay ! Instead, much better way is
to say the metric is (lets assume K1=K3=1 and K2=K4=K5=0, for simplicity):
metric = 256 * ( K1 * EIGRP_BANDWIDTH + K3 * EIGRP_DELAY )
where
EIGRP_BANDWIDTH = 10^7 / min_bandwidth_on_path_in_kbps
EIGRP_DELAY = total bandwidth in 10uS (10uS is unit in which
delay is actually configured on the interface)
Now, lets see example:
#show ip eigrp topology 192.168.224.3 255.255.255.255
IP-EIGRP topology entry for 192.168.224.3/32
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 156160
Routing Descriptor Blocks:
65.195.140.4 (FastEthernet0/0), from 65.195.140.4, Send flag is 0x0
Composite metric is (156160/128256), Route is External
Vector metric:
Minimum bandwidth is 100000 Kbit
Total delay is 5100 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1
External data:
Originating router is 192.168.224.3
AS number of route is 0
External protocol is Connected, external metric is 0
Administrator tag is 0 (0x00000000)
So, EIGRP_BANDWIDTH = 10^7 / 10^5 = 10^2 = 100
EIGRP_DELAY = 5100 / 10 = 510
metric = 256 * ( 100 + 510 ) = 256 * 610 = 156160 , exactly as reported by
"show ip eigrp topology" and "show ip route" command.
Help this clear confusion :)
Regards,
Sasa
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=21068&t=20926
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