Unusual QoS Issue on cisco 3750s

Posted on 2009-04-23
Last Modified: 2012-06-27
We are having a problem implementing QoS on our cisco kit and I would be grateful if anyone can suggest a suitable low cost solution to this issue. The problem is as follows: We use cisco 3750s in our remote sites which connect via 2mb leased lines to a couple of 3750s in our main site. Instead of using routers we use the Paradyne Network extender kit (These basically allow the switches to talk to each other as if they were directly connected) The problem is that we cannot tell QoS to only use 2mb of the 100mb ports on the 3750. The problem is that 10 % is the lowest you can define using the srr-queue bandwidth limit command. This would obviously utilise 10mb but  as far as the switch is concerned there is no congestion so QoS never kicks in even though the physical link can only hande 2mb. One way we tried to get around this was setting the speed of the 100mb interface to 10mb and using the following config to tell QoS that only 20% of the interface speed should be used: srr-queue bandwidth limit 20.   We then found that the Paradynes can only negotiate 10mb half-duplex so this option was no good. At our core site we could use an extra switch which would sit between the network extenders and the current switch. We could then negotiate 10mb full duplex between the two switches allowing QoS to work and could negotiate 100mb full duplex between the new switch and the Network Extenders. However this is not cost effective for our remote offices unless anyone knows of a 4 port switch that can have its speed and duplex settings fixed rather than left to auto-negotiate. If anyone can suggest something we are missing it would be greatly appreciated!
Question by:systems_mitsui
    LVL 32

    Expert Comment


    What model 3750? Metro does CAR. (rate-limit command)

    harbor235 ;}

    Author Comment

    They are IPServices. Unfortunately CAR is not available.
    LVL 32

    Accepted Solution


    aah, thats why I asked if you had the 3750 METRO, it does have CAR, it's the only one in the 3750 series.

    How about "mls qos aggregate-policer " command does your model have that?

    Which model do you have exactly and with what image?

    harbor235 ;}


    Featured Post

    Better Security Awareness With Threat Intelligence

    See how one of the leading financial services organizations uses Recorded Future as part of a holistic threat intelligence program to promote security awareness and proactively and efficiently identify threats.

    Join & Write a Comment

    I eventually solved a perplexing problem setting up telnet for a new switch.  I installed a new Cisco WS-03560X-24P switch connected to an existing Cisco 4506 running a WS-X4013-10GE Sup II-Plus. After configuring vlans and trunking,  I could no…
    David Varnum recently wrote up his impressions of PRTG, based on a presentation by my colleague Christian at Tech Field Day at VMworld in Barcelona. Thanks David, for your detailed and honest evaluation!
    After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
    Here's a very brief overview of the methods PRTG Network Monitor ( offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…

    745 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    15 Experts available now in Live!

    Get 1:1 Help Now