Rate Limiting Question

Discussion in 'Cisco' started by sim_wat1, Oct 29, 2008.

  1. sim_wat1

    sim_wat1 Guest

    Hi All

    My company has a 12Mbps LES Circuit internet link. We are starting to
    provide video conferences over the internet using the 12Mbps link.
    What I
    would like to do is by using rate limiting is guarantee say 3Mbps
    Bandwidth to video conferences which would mean all other internet
    would be restricted to 9Mbps I persume using access-lists in the rate-
    command is required, but can I set up all the rate-limit commands on
    one interface.

    Many Thanks in Advance

    sim_wat1, Oct 29, 2008
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  2. sim_wat1

    Darren Green Guest

    Hi Simon,

    I was interested in you post as I was not too familiar with the rate
    limiting command. A quick Google returned up a similar post:


    Explained it well enough for me, hope it helps.

    I wouldn't have necessarily done it this way, although rate-limiting
    seems very straightforward. As with all things you may be able to
    achieve the same end result a matter of different ways. For example,
    priority lists:


    and Cisco Modular QoS framework where you can classify, mark, police,
    shape etc.

    Note some of these features may only be supported inbound and others
    outbound. I must say though if it is simplicity you are after,
    rate-limiting may be just the ticket as it seems that you can do both.
    One has to remember though that unless your upstream provider is
    guaranteeing / differentiating your traffic as it traverses their
    network, your traffic control starts & ends at your router.


    Darren Green, Oct 29, 2008
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  3. sim_wat1

    Stephen Guest

    no, or not sufficient - as this only affects outgoing traffic.

    rate limiting only affects your outbound traffic, but doesnt control
    what comes in.

    i suggest you ask the supplier if there is anything they can do at
    their end to give a priority & limiting to your video conf stuff.....

    they may be able to control traffic based on IP address if you can use
    different addresses for video conf traffic and other stuff.
    Stephen, Oct 29, 2008
  4. sim_wat1

    bod43 Guest

    You dont say which platform you are considering?

    For a software router (i.e. not a switch) -

    Firstly the router needs to be able to identify the traffic.
    Mostly an access list will do. Consider NBAR if needed.

    For outbound traffic:-
    You can use the simple interface rate-limit command.
    (config-if)#rate-limit input access-group .....
    An example without an ACL
    rate-limit output 32000 2000 2000 conform-action
    transmit exceed-action drop

    Alternatively if you use Low Latency Queuing
    you will be able to keep you 12M internet link
    when there is no Video conf and allow the
    VC traffic priority when it is present.
    You can also set the dscp field in the traffic
    since one day some ISPs may support it.
    Maybe they do today?

    For inbound traffic.
    As already stated you cannot affect inbound traffic.
    UNLESS that is it is TCP or other blockwise
    acknowledged traffic.

    Since by far the majority of Internet traffic IS TCP then
    you can affect it - if your usage is typical.

    One caveat is that I have made this all up
    myself and it is not from any recognised authority
    however I have deployed it in real networks and it
    seems to work.

    Just apply the same traffic controls on the
    inside interface for inbound internet traffic as you did
    on the outside for outbound traffic. I use slightly
    more conservative rates say allow 4M for the video.

    What happens is that when the non video traffic
    exceed its quota one or more packets get dropped.
    This *sends a message* to the sending TCP
    which reduces its sending rate.
    By send a message I really mean this literally.
    This is *exactly* how TCP works. The loss of a packet
    is eventualy noticed by the sender which acts
    on the information.

    I have noticed that the rate-limit input command
    can be entered on an interface.

    rate-limit input 20000 3000 3000 conform-action
    transmit exceed-action transmit
    Not sure if this works.

    Good luck.
    bod43, Oct 30, 2008
  5. sim_wat1


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