[c-nsp] Egress QoS on FE links with less than 100Mbps speeds

[Bielawa, Daniel W. (NS)]

Hello,
	We had the same issue on couple of links. We solved it with the following command. The number on the end is a percentage of link speed in 1 percent increments. This was done on a 3750G running 12.2(44)SE6, this command might or might not work on other platforms.

 srr-queue bandwidth limit (10-90)

Thank You

Daniel Bielawa 
Network Engineer
Liberty University Network Services
Email: dwbielawa at liberty.edu
Phone: 434-592-7987
        

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Lobo
Sent: Wednesday, December 16, 2009 8:45 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Egress QoS on FE links with less than 100Mbps speeds

We're doing some Catalyst testing to roll out QoS on our Ethernet 
network and have come up against a hurdle.  On most of our backbone 
links in a MAN, the actual bandwidth between one C/O to another C/O is 
not always 100Mbps.  There are times when the link is only capable of 
hitting say 80Mbps (we're a wireless isp) or less.

Since we have to use a FE port for this type of connection, do the 
switches believe that they have 100Mbps of bandwidth to play with when 
putting packets into the appropriate queues?

I'm a bit confused as to how the switches work in this fashion.  If I 
were using CAT5 cables or fiber this would be simple to understand as 
the bandwidth would be fixed.  :)

This is an example of a configuration on a 3550-24 that I'm using:


interface FastEthernet0/x
mls qos trust dscp
wrr-queue bandwidth 40 35 25 1
wrr-queue cos-map 1 0 1
wrr-queue cos-map 2 2
wrr-queue cos-map 3 3 4 6 7
wrr-queue cos-map 4 5
priority-queue out
!

The switches that we use are 2950, 3550, 3750 and 6524s.

With MQC and "layer 3" QoS, I would know how to fix this by simply using 
the "bandwidth" command on the physical interface and basing my output 
policy-map to use "bandwidth percent" for each class.  Layer 2 QoS 
doesn't seem to work this way though.

Any help would be appreciated.

Thanks.

Jose
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