Serial Interface: Clock Rate bandwidth

[Kaushik Ray]

Hello

I would be grateful if someone can advice me on this:

I have a WAN link with capacity of 2560Kbps. I was looking at Solarwinds for the interface and see that the interface is capped at 2Mbps. While checking through the interface I see that the Serial interface is configured as follows:

interface Serial0/1/0

bandwidth 2560

no ip address

load-interval 30

no fair-queue

clock rate 2000000

end

Could the clock rate set as 2000000 be capping the bandwidth? I wanted to change it and the next available clockrate is

4000000; should i then set it to this value?

Thanks

[Jan Hrnko]

Hi,

Well, clock rate command does not limit the speed of the link, it sets it. I suppose that the interface will not work properly with 4Mbps clock settings and I am not sure if it even allows you to set it that high.

As for bandwidth command, it is there for other purposes, not for setting the speed of the link - as you certainly know.

Best regards,

Jan

[Kaushik Ray]

Jan

thanks for your reply.

I checked the other Serial interface which is in a down state and could put the 4Mbps in it. But if you think it would not work properly with the 4Mbps clock settings what do you suggest putting in for me to be able to allow the whole 2560Kbps?

thanks

[Kaushik Ray]

Here are the two interfaces for the WIC-2T the first one is the live one and second one is in down state.

Router#sh run int s 0/1/0

Building configuration...

Current configuration : 237 bytes

!

interface Serial0/1/0

bandwidth 2560

no ip address

load-interval 30

no fair-queue

clock rate 2000000

end

Router#sh run int s 0/1/1

Building configuration...

Current configuration : 74 bytes

!

interface Serial0/1/1

no ip address

shutdown

clock rate 4000000

end

When I tried to put a clock rate of 2560000 it did not accept

Router(config)#int s 0/1/1

Router(config-if)#clock rate 2560000

clock rate 2560000 is not supported

[Jan Hrnko]

Hi,

Unluckily, I am not near any real device and lab is not sufficient. However, I do remember that in some versions of IOS, you could set the clock rate higher than actual bandwidth that your device can provide.

I found this statement from one of the members of CSC,fsebera:

Cisco IOS/Serial hardware  will dynamically clock to the highest level the hardware supports if you  select a clock rate higher than the actual hardware interface rate.

That would be worth testing. I mean, if it works properly on your hardware and with your IOS. May I kindly ask you, which version of IOS do you use?

Best regards,

Jan

[Kaushik Ray]

Hi Jan thanks for your reply:

the IOS version on the router is c2800nm-advipservicesk9-mz.124-22.T5.bin

I tried to change the clock rate to 4000000 but I saw the traffic starting to reduce which is when I reverted back to the 2000000 but it goes back to being capped on the 2Mbps.

Is there any way round it?

[Kaushik Ray]

When i set the clockrate to 4000000, the next available clock rate more than 2560Kbps the traffic goes down as shown below. Did a shut / no shut on the interface and kept it for 5 minutes but still the input rate stays low: as soon as I put the clock rate back to 2000000, in 90 secs it goes back to 1.8Mbps.

Router#sh int s 0/1/0

Serial0/1/0 is up, line protocol is up

  Hardware is GT96K Serial

  MTU 1500 bytes, BW 2560 Kbit/sec, DLY 20000 usec,

     reliability 255/255, txload 55/255, rxload 86/255

  Encapsulation HDLC, loopback not set

  Keepalive set (10 sec)

  CRC checking enabled

  Last input never, output 00:00:31, output hang never

  Last clearing of "show interface" counters 00:05:27

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  30 second input rate 865000 bits/sec, 397 packets/sec

  30 second output rate 560000 bits/sec, 457 packets/sec

     116608 packets input, 36336001 bytes, 0 no buffer

     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

     125447 packets output, 19471391 bytes, 0 underruns

     0 output errors, 0 collisions, 0 interface resets

     0 unknown protocol drops

     0 output buffer failures, 0 output buffers swapped out

     0 carrier transitions

     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

Router(config)#int s 0/1/0

Router(config-if)#cl

Router(config-if)#cloc

Router(config-if)#clock ra

Router(config-if)#clock rate 2000000

Router#sh int s 0/1/0

Serial0/1/0 is up, line protocol is up

  Hardware is GT96K Serial

  MTU 1500 bytes, BW 2560 Kbit/sec, DLY 20000 usec,

     reliability 255/255, txload 54/255, rxload 182/255

  Encapsulation HDLC, loopback not set

  Keepalive set (10 sec)

  CRC checking enabled

  Last input never, output 00:00:14, output hang never

  Last clearing of "show interface" counters 00:07:10

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  30 second input rate 1834000 bits/sec, 563 packets/sec

  30 second output rate 549000 bits/sec, 540 packets/sec

     171380 packets input, 58179819 bytes, 0 no buffer

     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

     179102 packets output, 26116335 bytes, 0 underruns

     0 output errors, 0 collisions, 1 interface resets

     0 unknown protocol drops

     0 output buffer failures, 0 output buffers swapped out

     0 carrier transitions

     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up

Router#

[Kaushik Ray]

Is there any way to overcome this?

[paolo bevilacqua]

Kaushik Ray wrote:
Is there any way to overcome this?

No.

[Kaushik Ray]

Thanks Paolo for your response; i was thinking changing the WIC-2T to HWIC-2T / 4T; this could help?

regards

Kaushik

[paolo bevilacqua]

Kaushik Ray wrote:
Thanks Paolo for your response; i was thinking changing the WIC-2T to HWIC-2T / 4T; this could help?

No. What are you trying to do ?

[Kaushik Ray]

There is a our router and a client router back to back and the traffic is getting upto a max of 2Mbps as the clockrate is 2000000 on the DCE side (which is our Router). but the total capacity of the WAN link is 2560Kbps. When i change the clock to the next available rate which is 4000000, the traffic passing is starting to go down. when i revert back the clock rate to 2000000 it goes back upto the max 2Mbps again but not beyond that.

[paolo bevilacqua]

Ask telco to give you an ethernet interface that uses the full link capacity.

[Kaushik Ray]

Thanks Paolo for the response but actually the connection is back to back to the client router in the same rack there is no telco in between.

[paolo bevilacqua · Accepted solution]

Then just use an ethernet connection.