Trying to emluate T1 bandwidth on LAN switchport

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Sep 29th, 2008
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Hello all,


I am trying to do a test of some thin clients internally at my office and I want to emulate T1 bandwidth on a switchport so I can get an idea of how they will perform at the other end of a T1 link.


I have been using a policy-map to achieve the bandwidth policing, but I am not sure it is working. Here is what I have done: (G0/2 is the downlink port to the switch the thin clients are connected to.)


policy-map Test_Limit

class class-default

police 1544000 193000 exceed-action drop



interface GigabitEthernet0/2

description Trunk to test switch

switchport mode trunk

service-policy output Test_Limit



I used one of those bandwidth testers on the Internet and got the 9.3Mb/s result both before and after I applied the policy.


Am I doing this correctly, or is there a better way?


For reference, the switch I am applying the policy on is a C3560-24PS running 12.2(25)SEE and the test switch with the thin clients is a C2960-24TT-L running 12.2(35)SE5.


Thanks,


Chris

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Giuseppe Larosa Mon, 09/29/2008 - 09:12
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Hello Chris,

if you want to emulate T1 bandwidth you need to do it in both directions

use a second policy-map for inbound direction

make it similar to the first and apply it inbound


policy-map Test_Limit_IN

class class-default

police 1544000 193000 exceed-action drop


int gi0/2

service-policy output Test_Limit

service-policy input Test_Limit_IN


to verify if the commands are effective use


sh policy-map int


if no matches they are bypassed by multilayer switching


there is a limitation on this platform:


Follow these guidelines when configuring policy maps on physical ports:


•You can attach only one policy map per ingress port.


see


http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_see/configuration/guide/swqos.html#wp1044737


This would explain your results with and without the policer


if I understand correctly the policer is supported only inbound on a physical interface


Hope to help

Giuseppe


Joseph W. Doherty Mon, 09/29/2008 - 09:14
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". . . or is there a better way?"


The problem with policers, they don't emulate a slower interface which usually also queues overspeed traffic. A shaper would be a better choice for T1 emulation, but don't believe the 3560 supports it. However, the "srr-queue bandwidth limit" command should mimic the queuing better but it might not emulate the speed exactly. For best speed match, set port to 10 Mbps then set "srr-queue bandwidth limit" to 15(%).

olighec Mon, 09/29/2008 - 09:27
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Thanks for the replies, guys. I think I will try the srr-queue bandwidth limit command. Unfortunately I already tried applying and input and output policy, but the switch would not allow me to apply a policy in the input direction.


Thanks!

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