Adding costs to serial interfaces on router

[whiteford]

Hi,

I have a 3 sites (in a lab) connected to each other in a triangle formation (see attachment). The IP protocol in use is EIGRP and I want to change the routig so it one serial link has a very low bandwith and the other is fast how can I make sure traffic uses the fast link and not the slow link?

FOr example on the diag say on "Router A" serial 0/1 is 256k and serial 0/0 is 10mb, what woudl I need to add to both serial interfaces on all routers?

Thanks

[Giuseppe Larosa]

Hello Andy,

>> so it one serial link has a very low bandwith and the other is fast how can I make sure traffic uses the fast link and not the slow link?

EIGRP metric with default settings use two parameters:

delay

bandwidth

the EIGRP metric is cumulative on delay:

the delays of all links in the path are added expressed in tens of microseconds

256 * (delay1 + delay2 + ...)

the EIGRP metric component for BW is calculated in a different manner:

of all bandwidths the lowest value is used the component is calculated as:

256 * 10,000,000 / min_BW_in_path [kbps]

After all this long speech if you change the bandwidth parameter only in general you are not sure to influence the path that is chosen.

In the case of EIGRP is better to change/modify the delay because this has a more direct effect

Having a full mesh of three routers if you increase the delay.

Hope to help

Giuseppe