NAT overload pool size

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Jul 31st, 2008
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This question involves a basic NAT overload setup using a 6500/Sup720 with native IOS. The plan is to have student

wireless traffic (using private IP's) PAT'd to public IP(s) as it is routed to the Internet.

Since I don't have any large scale NAT experience I have a question ...

- If I have 500-1000+ concurrent web users, will one overload IP be enough ? If not, any real world experiences

on how big my overload pool should be ?


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simondarlington Fri, 08/01/2008 - 02:03
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I just came across this yesterday in my CCIE written studies.

Each inside global IP can support 65,000 concurrent tcp and udp flows (source Odom CCIE Written Exam Cert Guide)


lee.reade Fri, 08/01/2008 - 02:15
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Just to add, PAT is Port Address Translation, so your limiting factor would be how many ports can tcp/udp support and that is 65535.



lamav Fri, 08/01/2008 - 04:21
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The 65,000 number is true, in theory, but in reality, engineers who have actually tested this in a controlled environment estimate that the real number is about 4,000 -- and even then it depends on CPU strength, memory availability and allocation, and probably a few other factors.




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