changing eigrp route

[carl_townshend]

Hi all, can anyone tell me how eigrp knows what the bandwidth of a link is, what effect will keying the bandwidth statement have on the interface with eigrp ?

[andrew.burns]

Hi,

If you don't specifically configure a bandwidth then eigrp uses the default bandwidth for the interface (do a "show interface" to see the default bandwidth).

If you change the bandwidth using the bandwidth statement then you directly influence how eigrp calculates it's metric, a good example is in this document:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800c2d96.shtml

That said, best practise is to set the bandwidth accurately and change the delay if you need to modify the eigrp metric.

HTH - please rate if it does

Andrew.

[carl_townshend]

i gather i would make the delay lower to make it choose a given link ? , and up the bandwidth, if I dont change this I gather it would go off the delay, add them up as it goes along and use the lowest ?

[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

HTH

Andrew.