Bandwidth Division inside a LAN

Unanswered Question
Jul 31st, 2009

Hi All,

Is is possible to divide bandwidth equally, say between four depts in a office, using any of the catalyst switches like 3500.

in short can we implement Qos on switches.

I have this problem too.
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Joseph W. Doherty Fri, 07/31/2009 - 03:44

Many advanced Cataylst switches support some QoS features, but features vary much by platform (and sometimes IOS image).

Unclear exactly what you mean by "to divide bandwidth equally". Assuming your four depts. have equal access to the bandwidth, you could condsider that equal division. Or, you might limit each dept. to 1/4 total bandwidth (which precludes each dept. from using otherwise unused bandwidth). Or, you might distribute your four depts.' traffic to four queues and dequeue each equally (this would better balance traffic that tends to conflict, such as TCP vs. non-TCP).

Again, QoS features vary much by platform. For the 2900 XL and 3500 XL, in their latest software config. guide, found this:

Quality of Service and Class of Service

•IEEE 802.1p class of service (CoS) with two priority queues on the switch 10/100 and LRE ports and eight priority queues on the Gigabit ports for prioritizing mission-critical and time-sensitive traffic from data, voice, and telephony applications

•Voice VLAN (VVID) for creating subnets for voice traffic from Cisco IP Phones

More information about QoS on this switch can be found here:



If the switch was a 3550, it's QoS is more featured. See:

ravinderrajput Fri, 07/31/2009 - 04:06

Thanks a lot for the reply, the link posted has lot of gud info about Qos. I said "to divide bandwidth equally" because our company would be getting 8mb of internet b/w and dividing it equally among the four detps. the policy should be that the dept. use more than 2mb only if the b/w is available and not otherwise

Joseph W. Doherty Fri, 07/31/2009 - 04:18

Ah, for Internet bandwidth, you can often well (or better) control outbound traffic, especially if you use a router (or some of the MetroE switches), but inbound bandwidth control, even on routers, isn't too great unless you determine QoS on the other side of the Internet link (i.e. the ISP side).

If the inbound bandwidth control is important to you, and you're limited to just your side of the Internet link, don't believe any of the current Cisco products will fully satisfy. Some 3rd party products might for TCP, like Packeteer's, but non-TCP traffic is still a problem.

ravinderrajput Fri, 07/31/2009 - 04:32

please see the n/w diagram of our office. The internet b/w is available at the earth station and the H.O is connected to it via a microwave link. H.O uses the b/w of the earth station. Recently there has been lot of fuss about the speed and latency issues and one depts blaming each other for "misusing" b/w Now the company wants to have a separate links(both at earth station- e.s) for the e.s and the H.O. The E.S would be getting 4mb link and the H.O would be getting 8mb this 8mb has to be divided equally among the detps so that no one complains that the other is getting more b/w. That's y we r planning to implement QoS on the LAN. Are there any other ways by which we can control b/w usages by the depts.

Can you please elaborate when you say

"unless you determine QoS on the other side of the Internet link (i.e. the ISP side)."

Joseph W. Doherty Fri, 07/31/2009 - 16:17

"Are there any other ways by which we can control b/w usages by the depts."

Again, depends on the platforms involved, and a 3500 is far from ideal. It also depends on where the congestion issues is, i.e. the link to/from your ISP or across the microwave link. With the right platform the microwave link would be easy to manage.

If you control the router shown on your diagram that connects to the ISP, again depending on your platform and IOS, you might have something like:

policy-map CBWFQ

class default-class



policy-map CBWFQ

class deptA

bandwidth percent 20

class deptB

bandwidth percent 10

interface (WAN link to ISP; or microwave outbound)

service-policy outbound CBWFQ

Inbound you're very limited to what you can effectively do (well). Beside looking at different links (which might still benefit from the above for your microwave links), 3rd party products, like Packeteer's, can better influence inbound TCP traffic.


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