Re: Port numbers and IPv6

["Stephen Sprunk" <stephen at sprunk.org>]

Thus spake "Noel Chiappa" <jnc at mercury.lcs.mit.edu>
>    > From: Ned Freed <ned.freed at mrochek.com>
>
> Let me make sure I understand you here:
>
>    > IMAP4 has the characteristic that you often have a huge number
>    > of incoming connections, only a few of which are active at any
>    > given time.  Designing servers to accomodate huge numbers of
>    > connections is a bit tricky, but workable: ...
>    > The 65536 limit, OTOH, has to be dealt with by using multiple
>    > server IP addresses, which in turn usually require multiple
>    > interfaces ...
>    > ... that doesn't mean nobody is hitting the 65536 limit imposed by
>    > source port numbers. They are, it causes problems
>
> You're saying that there are servers which have close to (or more)
> than 65K connections to a *single client IP address* (i.e. it may be a
> NAT, with a number of hosts behind it)? (If a server is talking to a
> number of different client IP addresses, it can have up to 65K
> connections to *each*.)

That assumes the client is directly talking to the IMAP server.  Some 
servers are behind an "SSL accelerator" such that all connections come from 
a single IP address, so only 64k clients are possible.  Other servers may be 
behind a webmail application, with the same effect.

The number of folks experiencing this has to be pretty low, but it'd be a 
severe problem for them.

S

Stephen Sprunk      "Those people who think they know everything
CCIE #3723         are a great annoyance to those of us who do."
K5SSS                                             --Isaac Asimov 


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