Rate Limiting Question

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 MAX Bandwidth to video conferences which would mean all other internet traffic would be restricted to 9Mbps I persume using access-lists in the rate- limit command is required, but can I set up all the rate-limit commands on the one interface.

Many Thanks in Advance


Reply to
Loading thread data ...

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:

formatting link
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:

formatting link
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.



Reply to
Darren Green

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.

Reply to

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.

Reply to

Cabling-Design.com Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.