sub-optimal available bandwidth on serial interface

[GM2005]

Hi

I've got a serial interface set at 1536k but found today the available bandwidth is only 334k. Tried max-reserved-bandwidth 100, no change. Faulted it out to MPLS who called in AT&T but the circuit is running clean. Also, took off QoS policy, no change. Could use a pointer as I cannot take the interface down on a whim. No CRC or interface resets incrementing and no drops etc.

 

[ADB100]

I've got a serial interface set at 1536k but found today the available bandwidth is only 334k.

How are you verifying that the bandwidth is only 334Kbps? If this is a clock-rate thing, it is your SP that provides the serial interface clocking to your router - you can set the bandwidth parameter to whatever you want, it is used by routing protocols and QoS Policy-Maps, it DOESN'T dictate the interface speed.

Andy

 

[GM2005]

Thanks for that, it looks like a red herring. I'm mystified as to why it stayed after disabling the service-policy on the interface. The max-available-bandwidth 100 surely should have upped it by something shouldn't it. I have used it on IP Clear circuits and it made a difference there.

The show interface serial command shows this available bandwidth but if I enter the max-available-bandwidth 100 command on other routers in the network it alters the figure.

Users complaining of poor response prompted me to check. The circuit is not new and the response has just deteriorated recently. I checked the utilization but it's not the issue......

 

[ADB100]

OK I think understand now.

When you issue the command 'show queueung interface serial x' in the output it says 'Available Bandwidth 334 kilobits/sec'

If that's the case it means that after your egress service-policy allocates the bandwidth you have configured, plus the default reserved 25% the remaining bandwidth is 334Kbps.

I assume if you add up the bandwidths for each of your classes in your service policy they equal 818Kbps (1536 minus 25% = 1152 minus 334 = 818). That is assuming the bandwidth statement on the serial interface is 'bandwidth 1536000'

Changing the 'max-reserved-bandwidth' on the interface changes the default 25% that can't be allocated (either more or less). If you do change this make sure your service policy caters for your router sourced traffic (routing updates, keepalives, telnet etc).

HTH

Andy