Solved: 3750 switch: limiting bandwidth to 3 M

gavin han · ‎08-09-2011

Hi,

I 3750 doesn't support "shape" command under policy map. could you advise how do I limit the badwidth to 3 M? I did following but it didn't help:

interface GigabitEthernet1/0/4

no switchport

ip address 192.168.1.1 255.255.255.252

no ip route-cache cef

no ip route-cache

no ip mroute-cache

speed 100

srr-queue bandwidth limit 30

Richard Michael · ‎08-09-2011

Hello Gavin,

We cannot do class based egress rate-limiting on 3750. One way to do egress rate-limiting is using: 'srr-queue bandwidth limit' command. However, using this we cannot selectively do rate-limiting for only a certain class

of traffic like we can for ingress rate-limiting. It is used for limiting the bandwidth on an egress interface and is documented in the link below,

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_44_se/configuration/guide/swqos.html#wp1253412

When you configure this command to 80 percent, the port is idle 20 percent of the time. The line rate drops to 80 percent of the connected speed, which is 800 Mb/s. These values are not exact because the hardware adjusts the

line rate in increments of six. Also we cannot configure this on the 10-Gigabit interfaces.

An alternate way is to set the dscp of all traffic to a single value(Using class-maps) and to map only that dscp to a certain queue(For eg; "mls qos srr-queue output dscp-map queue 1 threshold 1 "). This way all

the traffic passes via a certain queue. Then we could shape the traffic of that queue using the command, "srr-queue bandwidth shape" command. The "srr-queue bandwidth shape" command is discussed below,

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/1 2.2_25_se/configuration/guide/swqos.html#wp1163879

There is no way to perform class based egress rate-limiting on the 3750. The only way to do

egress limiting is by 'srr-queue bandwidth limit' command (or) the "srr-queue bandwidth shape" command on this particular platform as shown above.

Thanks,

Ricky Micky

*Please rate if the content was useful

View solution in original post

Richard Michael · ‎08-09-2011

Hello Gavin,

We cannot do class based egress rate-limiting on 3750. One way to do egress rate-limiting is using: 'srr-queue bandwidth limit' command. However, using this we cannot selectively do rate-limiting for only a certain class

of traffic like we can for ingress rate-limiting. It is used for limiting the bandwidth on an egress interface and is documented in the link below,

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_44_se/configuration/guide/swqos.html#wp1253412

When you configure this command to 80 percent, the port is idle 20 percent of the time. The line rate drops to 80 percent of the connected speed, which is 800 Mb/s. These values are not exact because the hardware adjusts the

line rate in increments of six. Also we cannot configure this on the 10-Gigabit interfaces.

An alternate way is to set the dscp of all traffic to a single value(Using class-maps) and to map only that dscp to a certain queue(For eg; "mls qos srr-queue output dscp-map queue 1 threshold 1 "). This way all

the traffic passes via a certain queue. Then we could shape the traffic of that queue using the command, "srr-queue bandwidth shape" command. The "srr-queue bandwidth shape" command is discussed below,

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/1 2.2_25_se/configuration/guide/swqos.html#wp1163879

There is no way to perform class based egress rate-limiting on the 3750. The only way to do

egress limiting is by 'srr-queue bandwidth limit' command (or) the "srr-queue bandwidth shape" command on this particular platform as shown above.

Thanks,

Ricky Micky

*Please rate if the content was useful

Edson Vuma · ‎03-18-2013

Hi, Richard

I am using this switch model: WS-C3750X-48P, with this IOS: C3750E-UNIVERSALK9-M.

I realized that I cant do that limitation of bandwidth using the SERVICE-POLICY.

My questions are:
1.

If I upgrade the IOS to IP SERVICES, will I be able to make this configurations?

2.

With this command:

Switch(config-if)# srr-queue bandwidth ?
  limit              Configure bandwidth-limit for this interface
  shape             Configure shaping on transmit queues
  share              Configure shared bandwidth

Having a 30Mbps Internet link, knowing that this switch has GigabitEthernet ports, how I can configure a limitation of 3Mbps on an interface?

Best wishes

--
Regards
Edson Vuma

-- Regards Edson Vuma

Joseph W. Doherty · ‎03-18-2013

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

You have two options on an ordinary 3750.

You can "shape" the interface with the srr-queue bandwidth limit command. However, it's not exact and for 3 Mbps you would need 30% of 10 Mbps link rate (minimum value is 10, which would be about 10 Mbps if link was 100 Mbps.)

With QoS enabled, you can shape individual egress queues with the srr-queue bandwidth shape command. If you direct all traffic to just one queue, you could shape it for 3 Mbps using the inverse weight ratio. For example, a weight of 33 would be about 3 Mbps of 100 Mbps.

PS:

If yours was a ME3750, you have additional options with the ES ports.