serial bandwidth showing BW 2048 Kbit instead of 1544 Kbit

[kchun]

We current use a T1 bandwidth line on our Cisco 3600 router but when I issue a show int command, it is showing the BW as 2048 Kbit insteado of 1544 Kbit. Is there is reason why this happens? It's a QUICC serial.

[svermill]

Bandwith is a label that you apply to the interface. It is used by some routing protocols to calculate metric and also by EIGPR over frame relay to determine how many bits per second it can use for routing updates, etc. Has no effect on throughput. Should be manually set to match your line speed.

[kchun]

Yes, but by default shouldn't it only see the bw as 1544Kbit? This is just a standard T1 and I see that it's only happening to this router that it sees the serial interface as BW 2048Kbit. All my other routers are seeing 1544Kbit except this one. If I manually set the bandwidth for this interface to 1544Kbit, will this have any effects on the router/interface?

thanks you for your inputs.

[svermill]

Yes, the factory default is 1544 kbps. If you 'sh run' you will see that someone, at some point, changed that value in the config. Changing it will have zero impact on the interface itsef. HOWEVER, if you are running OSPF, EIGRP, or IGRP, you will be changing the metric for routes via that interface. This will likely inturrupt traffic while the metrics are recalculated (and possibly routes re-routed).

[kchun]

No, the show run did not indicate that the BW was changed. There are no BW setting tied to the serial interface. If that's the case, will this indicate that something else is changing the BW setting for the serial interface?

thanks.

[millerv]

might it be an E1 interface ?

[kchun]

It's a QUICC serial.

[infowhiz]

try performing a "show controllers serial x" command and do an output comparision between another router's controllers output. Also, check the cable and try to replace it. An interesting fact is that the max capability of a serial interface is 2MBits.

If nothing above works, make sure to MANUALLY override the bandwidth setting by issuing the bandwidth command anyway. If you miss this step then EIGRP can take up to 50% of the bandwidth for itself (in your case it can be upto 1MB if you don't change the default 2mb).