how to give static bandwidtch

~ Cisco 1721 IOS 12.4 Adv.Security. ~ How to give static bandwidth 256kbps ~ to download and 64kbps to upload ~ for user connected to FastEthernet0? ~ This LAN is only for Internet sharing. ~

CAR should be able to do it:

Aaron

It's no longer necessary to use CAR. There is a better method known as policing. which has the same net effect as CAR, but policing can be applied to QoS class and therefore there is more options to match traffic other then ACL's.

Also, take a little advice - for what you want to do it's better to shape traffic instead of dropping it (with policer or CAR). Shaping allows you to delay excessive traffic and this can have better net effect then dropping it. Shaper will drop traffic only when the queue fills up to the threshold and default is 64 packets which is appropriate in most cases. When you define shaper then you can nest CBWFQ inside of it to guarantee more bandwidth for some applications (when shaped) than to the others, etc.

Here is a sample config that shapes traffic to "small ISP" customers up to the 1000000 bps respectively, and gives them ability to upload up to 512000 bps respectively (you need to define class-maps for this example to work - see the link above!):

policy-map simpleISP=>upstream ISP class CustomerA shape average 512000 class CustomerB shape average 512000

policy-map simpleISP=>customers class CustomerA shape average 1000000 class Customer B shape average 1000000

Interface fa0/0 description simpleIPS=>customers service-policy output simpleISP=>customers

Interface s0/0/0.477 description simpleISP=>upstream ISP service-policy output simpleISP=>upstream ISP

Checking example: sh policy-map int fa0/0

If you have some additional questions about Cisco IOS QoS fill free to ask...

B.R. Igor

Thank you very much. I have question ;) In many traffic policing examles is for instance: police 8000 2000 4000 conform-action transmit exceed-action drop, but you suggest to use shape average. What are diferences?

Because 'police' IOS command if followed with drop statement drops packets instead of holding them in the queue... This can be good for TCP traffic, but in most cases it's better to shape all the traffic and use WRED to randomly (and intelligently) drop packets based on CoS marks and use CBWFQ (if this is data traffic) to guarantee bandwidth for some classes. If you only shape traffic then be aware that this increases delay, but on the other side dropping all TCP traffic that exceeds some defined rate and consisting of multiple flows at once can cause so called global synchronization

which is not good traffic behavior. However,whether using policer or WRED for dropping packets, note that UDP and ICMP traffic could result in broken communication if dropped so UDP best works if it's shaped... In your case it's best to only shape traffic for your customers if you are planning to treat all traffic equally. The only drawback of this solutuion is that you cannot offer full link capacity to one of your customers if the others doesn't use the link which I do for my customers using CBWFQ and for now I don't have any UDP communication problems reported, but I don't drop or shape DNS and ICMP traffic...Of course, real big IPS's don't do CBWFQ - they usually only shape all the traffic unless SLA doesn't requires different treatment.

Traffic policer ('police' or CAR in Cisco case) is useful for 2 things:

- smart packet markings - mark down packets with different CoS depending of traffic rate - for example: you may mark down FTP traffic with cs1 it it exceeds the rate of 512 kbps. This enables you to give that traffic lower priority and higher drop probability when using WRED if it starts using too much bandwidth.

- When using LLQ for VoIP then it's useful to give that traffic strict priority, but to avoid starvation of lower priority data traffic you should limit strict priority traffic so that it doesn't occupies the whole available bandwidth.

B.R. Igor

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