In message <20050715205554.15355872E3@xxxxxxxxxxxxxxxxxxx>, Noel Chiappa writes : > > From: Ned Freed <ned.freed@xxxxxxxxxxx> > >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 _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf