From: Chuck Church (cchurch@MAGNACOM.com)
Date: Tue Oct 15 2002 - 22:42:29 GMT-3
Jason,
Are you sure about the load calculation? Someone (I think it was
Brian Dennis) mentioned a while ago that if you decided to include load, it
was only looked at initially when the EIGRP process started up. I never
found anything on CCO to support this, but it makes sense. If your
preferred routes changed based on load, they'd change again soon after the
load switched to somewhere else. It'd be a route flapping nightmare.
Anyone seen a document on CCO about this?
Chuck Church
CCIE #8776, MCNE, MCSE
Sr. Network Engineer
Magnacom Technologies
140 N. Rt. 303
Valley Cottage, NY 10989
845-267-4000
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Jason Sinclair
Sent: Tuesday, October 15, 2002 8:14 PM
To: 'Rick'; Ccielab (E-mail)
Subject: RE: EIGRP metric weights Question FOR EIGRP GURUS
Rick,
A little history is in order to understand why this command was introduced.
EIGRP was the post-IGRP routing protocol that Cisco developed utilising the
Diffusing Update Algorithm. That said, reliability and load were included as
configurable constants for backward compatibility with IGRP. It is not
recommended to manipulate these settings but to manipulate the delay factor
instead (k3 constant). If for example you were to include load as one of the
parameters for metric, what happens when the load changes (which is
generally calculated every 30 seconds)? Basically, a new update will be sent
because of the change in metric for the route.
If on other hand the lab should ask you to include load or reliability in
the metric calculation you would use k2 to include load and k5 to include
reliability.
Let me know if you would like more info.
Jason Sinclair CCIE #9100
Manager, Network Control Centre
POWERTEL
55 Clarence Street,
SYDNEY NSW 2000
AUSTRALIA
office: + 61 2 8264 3820
mobile: + 61 416 105 858
email: sinclairj@powertel.com.au
-----Original Message-----
From: Rick [mailto:ccie_2003@hotmail.com]
Sent: Wednesday, 16 October 2002 05:32
To: Ccielab (E-mail)
Subject: EIGRP metric weights Question FOR EIGRP GURUS
I'm trying to understand Why, and how to properly use this command. Could
someone further explain this command and give an example how to use it, or
how
it may be used on a lab scenario?
Thanks,
Rick
To allow the tuning of the IGRP or Enhanced IGRP (EIGRP) metric
calculations,
use the metric weights router configuration command. To reset the values to
their defaults, use the no form of this command.
metric weights tos k1 k2 k3 k4 k5
no metric weights
Syntax Description tos
Type of service. Currently, it must always be zero.
k1-k5
Constants that convert an IGRP or EIGRP metric vector into a scalar
quantity.
Defaults
tos: 0
k1: 1
k2: 0
k3: 1
k4: 0
k5: 0
Usage Guidelines
Use this command to alter the default behavior of IGRP routing and metric
computation and allow the tuning of the IGRP metric calculation for a
particular type of service (ToS).
If k5 equals 0, the composite IGRP or EIGRP metric is computed according to
the following formula:
metric = [k1 * bandwidth + (k2 * bandwidth)/(256 - load) + k3 * delay]
If k5 does not equal zero, an additional operation is performed:
metric = metric * [k5/(reliability + k4)]
Bandwidth is inverse minimum bandwidth of the path in bps scaled by a factor
of 2.56 * 1012. The range is from a 1200-bps line to 10 terabits per second.
Delay is in units of 10 microseconds. The range of delay is from 10
microseconds to 168 seconds. A delay of all ones indicates that the network
is
unreachable.
The delay parameter is stored in a 32-bit field, in increments of 39.1
nanoseconds. The range of delay is from 1 (39.1 nanoseconds) to hexadecimal
FFFFFFFF (decimal 4,294,967,040 nanoseconds). A delay of all ones (that is,
a
delay of hexadecimal FFFFFFFF) indicates that the network is unreachable.
Table 19 lists the default values used for several common media.
Table 19: Bandwidth Values by Media Type Media Type Delay Bandwidth
Satellite
5120 (2 seconds)
5120 (500 megabits)
Ethernet
25600 (1 ms)
256000 (10 megabits)
1.544 Mbps
512000 (20,000 ms)
1,657,856 bits
64 kbps
512000 (20,000 ms)
40,000,000 bits
56 kbps
512000 (20,000 ms)
45,714,176 bits
10 kbps
512000 (20,000 ms)
256,000,000 bits
1 kbps
512000 (20,000 ms)
2,560,000,000 bits
Reliability is given as a fraction of 255. That is, 255 is 100 percent
reliability or a perfectly stable link.
Load is given as a fraction of 255. A load of 255 indicates a completely
saturated link.
Examples
The following example sets the metric weights to slightly different values
than the defaults:
router igrp 109
network 192.168.0.0
metric weights 0 2 0 2 0 0
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2002
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