serial, bandwidth statement

[carl_townshend]

Can I alter the way eigrp makes it path descisions by changing the bandwidth command on my serial interface ? and can you do this for ethernet etc also ?

[andrew.burns]

Hi,

to quote Cisco:

When you initially configure EIGRP, remember these two basic rules if you are attempting to influence EIGRP metrics:

* The bandwidth should always be set to the real bandwidth of the interface; multipoint serial links and other mismatched media speed situations are the exceptions to this rule.

* The delay should always be used to influence EIGRP routing decisions.

Because EIGRP uses the interface bandwidth to determine the rate at which to send packets, it is important that these be set correctly. If it is necessary to influence the path EIGRP chooses, always use delay to do so.

Normally, you would increase delay to make a route less-preferable, rather than the other way round.

This is from the following doc:

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml

So, yes you can use the bandwidth command (on any interface) to influence eigrp metrics, but as stated above, it's not recommended.

HTH

Andrew.

[Richard Burts]

The link and the explanation that Andrew provide is good. There is one other aspect to consider in which it is not recommended to change the bandwidth to alter the EIGRP metric. EIGRP advertises the lowest bandwidth along the path. So you might change the bandwidth but if there is some segment on the path with bandwidth lower than what you set then some parts of the network will see that lowest bandwidth not the bandwidth that you changes.

On the other hand EIGRP advertises the delay cumulative along the path. So if you change the delay then every part of the network will see the effect of your change.

So it is recommeded that you alter delay rather than bandwidth to influence EIGRP metric.

But if you still choose to do so you may alter the bandwidth to change the EIGRP metric. And yes you can also do that on Ethernet.

HTH

Rick