From: Hunt Lee (huntl@webcentral.com.au)
Date: Mon Sep 15 2003 - 22:39:17 GMT-3
Hi Tim,
Is there any scenario where you may wanted to set k4 & k5 to 1?
I have been working on a scenario, and it has both k4 & k5 set to 1.
"It has been seen lots of times, an ATM interface generates CRC errors on
either R6
or R9 routers of this lab. Configure EIGRP such upon getting such errors on
any
particular router will automatically reflect to EIGRP topology of all
routers in EIGRP
AS."
Yet they only set k4 and k5 to 1, but not k2...
So does that mean the metric will only care about reliability and mtu, but
not load?
Also, to fulfill the requirement, wouldn't it be better if I just set k4 =
1, but leave k5 as 0?
Thanks,
Hunt
-----Original Message-----
From: Snow, Tim [mailto:timothy.snow@eds.com]
Sent: Tuesday, 16 September 2003 11:29 AM
To: 'Nir Wittenberg'
Cc: 'ccielab@groupstudy.com'
Subject: RE: EIGRP metrics
Hopefully this well help, some of my eigrp notes when studying.
EIGRP uses a composite metric that is derived from the five submetrics. When
EIGRP computes the composite metric, it uses a formula that involves five
constants or "k" values. The constant values have default value such as the
following:
k1 = k3 = 1 and k2 = k4 = k5 = 0
By setting k2, k4, and k5 to 0, it essentially nullifies the submetrics of
load (k2) , reliability (k4) , and MTU (k5). This is precisely why you
should first use delay and then bandwidth when trying to influence which
routes EIGRP prefers. The formula EIGRP uses to calculate the composite
metric is as follows:
Metric = 256 x ([k1 x BWmim + (k2 x BWmim ) / (256-LOAD) + k3 x DELAYsum ]
x X)
where the following is true:
BWmim = 107 / bandwidth_of_slowest_link DELAYsum =
(delays_along_the_path) X = k5 / (reliability + k4) if and only if k1<>1,
if k1 = 1 then X = 1
With the k values set at the default value you have
k1 = k3 = 1 k2 = k4 = k5 = 0 CM = 256 x (BWmim + DELAYsum )
Using the default values of constants, k1 = k3 = 1 and k2 = k4 = k5 =0, the
formula quickly breaks down to this:
(256 x [BWmim and DELAYsum])
Substituting the constants, you have the following:
CM = 256 x ([1 x BWmim + (0 x BWmim) / (256-LOAD) + 1 x
DELAYsum] x 1) CM = 256 x ([BWmim + (0) / (256-LOAD) +
DELAYsum] x 1) CM = 256 x (BWmim + DELAYsum)
NOTE
For reference, the metric is computed the same way for IGRP, except the
result of bandwidth and delay is not multiplied by 256, and the DELAY sum
variable is divided by 10.
CM = (k1 x BWmin + [k2 x BWmin] / [256-LOAD] +
[k3 x DELAYsum] x X)
where the following is true:
BWmin = 107/ bandwidth_of_slowest_link DELAYsum
= S(delays_along_the_path) /10 X = k5 / (reliability + k4) if and only if
k1<>1, if k1=1 then
X=1 k1=k3=1 k2=k4=k5=0
With k values set at the default value, you have:
CM = BWmin + DELAYsum
In short, TOS is always 0, "metric weights TOS BANDWIDTH LOAD DELAY
RELIABILITY MTU"
Tim
#12042
-----Original Message-----
From: Nir Wittenberg [mailto:nwittenberg@msncomm.com]
Sent: Monday, September 15, 2003 7:40 PM
To: ccielab@groupstudy.com
Subject: EIGRP metrics
Do K1, K2, K3, K4, K5 correspond to Bandwidth, Delay, Reliability, Load, and
MTU respectively?
I ask because on a practice lab I was asked to have EIGRP take load into
account when determining a route metric.
My answer was:
metric weight 0 1 0 1 1 0
Their answer is:
metric weight 0 1 1 1 0 0
I have searched the archives and cisco, but still no clear answer.
TIA
Nir
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