In message
<20050715205554(_dot_)15355872E3(_at_)mercury(_dot_)lcs(_dot_)mit(_dot_)edu>,
Noel Chiappa writes
:
> From: Ned Freed <ned(_dot_)freed(_at_)mrochek(_dot_)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*.)
Ned isn't the first person I've heard this observation from. Yes,
there are some really large-scale systems that run into this limit.
Sure, there are work-arounds, such as assigning multiple IP addresses
to the server and using DNS-based load balancing. That doesn't change
the fact that the basic design has run afoul of an address space limit.
Circa 1974, in a computer architecture class, I heard Fred Brooks point
out that *every* successful computer design eventually ran out of address
space. The same applies to network protocols.
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb
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