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What determins bandwith allocation to simutaneous requests?

Posted on 2008-10-27
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Last Modified: 2013-11-05
I have 2 sites.. lets call them A and B.  each fed by a T1 leased line Internet connection..  both have PIX 515 connected to telco provided routers..  only difference between the 2 PIXes ... Site A has an unrestricted license and site B has a restricted license...  Site A NATs out from a pool of about 30 IPs..  Site B NATs out from 2 IPs and then switches to PAT...  

The behavior I'm seeing at site A is..  all simultaneous  downloads balance out, more or less. to use the full  1.5Mbit of the T1.. and general web browsing, SSH connections are largely unaffected..

At Site B on the other hand.. all simultaneous  downloads balance out, more or less to use the full  1.5Mbit  T1..  BUT general web browsing at this time CRAWLS at sub modem speeds, SSH connections are almost unusably slow..  yet if I start another download..  it will creep up in speed to roughly 1.5Mbit / # of downloads..  

hopefully this is making sense..   My question is ..  is it the PIX influencing this behavior?? the upstream router??  what?

Thanks in advance...
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Question by:razor192
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packetguy earned 500 total points
ID: 22819757
Port Address Translation shouldn't have any problem with NAT pool size. How many users is your restricted PIX licensed for? And are they both at the same software version level? Also, are the ISPs the same in both cases? If your PIXen are indeed hardware- and software-identical, then I would look in these places for the performance problem:

1. Replace the Ethernet cables. They go bad, since nothing is holding them together but friction. When they go bad, TCP/IP tries to get the traffic through, and succeeds. But very slowly.

2. Verify port speed and duplex settings. Generally on Cisco gear I say to hard-code these on the devices, and only connect them to managed switches so that you can hard-code the settings on the corresponding switchports. Speed/duplex mismatch is the number one cause of performance problems (after bad cables). Don't forget to get the Internet provider's CPE hard coded as well. Sometimes these might be 10BaseT interfaces, in which case you'll have to set the paired ports to 10 Mbps as well (half duplex will be fine for a 3Mbps link).

3. Validate your upstream ISP's  performance by connecting a notebook computer directly to their Ethernet port and running speed test such as those at http://www.dslreports.com. It could be your ISP.

These are the most common causes of poor multi-user throughput.

 -mel
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by:razor192
ID: 22824583
Thanks..  I'll take a look at the points you made..  
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by:razor192
ID: 22845856
it turned out to be a port speed mismatch between the PIX and the switch (that was running in unmanaged mode)  
When I put the switch into managed mode and specified the port setting on it and the PIX things are much better..
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