Limit speed of 3750 Gig port to 768

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Jan 5th, 2009
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We have a gig 3750 and want to limit the speed in and out of one of it's ports to 768 to simulate a fractional T1.

I'm having trouble finding the best way to do this.



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andrew.butterworth Mon, 01/05/2009 - 14:27
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It should be pretty easy to do this in the ingress direction with a service-policy, but you might struggle on egress as the 3750 can't do egress service-policies. However the 3750 supports bandwidth limiting on egress ports. This is configured as a percentage and can be in the range 10-100. So the best you are going to get is 1Mbps by restricting a port to 10Mbps and applying a bandwidth limit of 10%.

switch(config)# interface FastEthernet 1/0/1

switch(config-if)# speed 10

switch(config-if)# duplex full

switch(config-if)# srr-queue bandwidth limit 10

This might not achieve what you are looking for though as it works by making the link idle for X-percent of the time - i.e. in this case it would be idle for 90% of the time.

To configure the inbound policy you would do this:

switch(config)# policy-map Restrict-768Kbps

switch(config-pmap)# class class-default

switch(config-pmap-c)# police 786432 8000 exceed-action drop

switch(config)# interface FastEthernet 1/0/1

switch(config-if)# service-policy input Restrict-768Kbps

I haven't tested any of this but based on the documentation this is probably the best you can achieve. If you really want to simulate a fractional T1 why not get a pair of routers and a back-to-back serial cable and physically clock the link at 768Kbps? This would be a more realistic test.




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