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jkaftan

jkaftan

MIS
Apr 8, 2005
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I have been studying my internet traffic via NetFlow. I ahve a 30 Mbs connection. At times we experience issues with slowness and short dropps. I look at my netflow info and I can see that the connection spikes up to 100 Mbs (it is an ethernet handoff from the ISP) It looks to me that we are overloading the circuit.

I am planning on setting up a rate-limit on this interface. My question how does ethernet handle bandwidth allocation within the rate that I set? For example if I set the rate-limit to 30 Mbs on this connection and someone tries to download a big file what prevents that person from hogging all or most of the 30Mbs? It is just the CSMA/CD? Can I leave it up to the protocol to be fair to everyone or do I need a Packeteer type device? Thanks.
 
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Depends on the traffic, you could setup QoS and in your policy specify traffic you want to give lower priority like P2P. Then give your essential traffic higher priority.

CCNA MCSE MCP NET+ A+ Security+
 
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Yeah I am familular with QoS. Ok say you do not have QoS configured. There is only one user using the connection and they are downloading a big file. They should get 100% of the bandwidth - overhead assuming the source can keep up. In our case it would be 30 Mbs.

Now what if there are 400 people using the connection and the same user trys to download that file again? Who gets that 30 Mbs of bandwidth? Would that user beat everyone else out? Would all users get about the same download speed? If so how does that happen? What is the mechanisim to distribute bandwidth within the protocol?

Even if you do have QoS configured and everyone is using port 80 it would make no difference right?
 
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correct to limit specifi users you would need to put something else in place.

A cheap and easy way would be to proxy your internet with squid and use the delay pools

CCNA MCSE MCP NET+ A+ Security+
 
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Decisions regarding what packets to transmit, which to hold and which are dropped is entirely up to the queuing mechanism being employed. On Cisco routers high speed interfaces are normally fifo but you could elect to implement fair-queuing with or without weighted random detection. These queuing techniques attempt to distribute available bandwidth fairly between different flows and work to avoid a phenomenon called global tcp synchronization. What hardware are you running?

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I configured my router with the following line on both the interface that faces my ISP and the interface that faces my network. My goal is to just make sure we never exceed our CIR of 30 Mbs. I do not care about bursting I just never want to go over 30 Mbs period. Should this do the trick?

rate-limit input 30000000 30000000 30000000 conform-action transmit exceed-action drop.
 
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