It's always been my belief that the 576 values were generated by hosts that didn't support Path MTU discovery and wanted to be conservative and avoid fragmentation. Fair enough.. .... apparently there's some performance value in this (at least to the ....

MTU - at least this makes a little bit of sense.. If they're doing HTTP/1.0 stuff with parallel connections then a smaller MTU is going to make that parallelization latency much more effective and perceived performance will go up some.. it doesn't impact full document retrieval time though (at least not positively!).. are dial links really lossy enough that chopping the segment size to 1/3 is a big win in retransmit time or are the win95/98 stacks really braindead enough that they don't do pmtud so are just trying to dodge fragmentation? I found it really odd that [7] which I use all the time to track features in a myriad of shipped OS's actually has a blank entry for pmtud on both of those (neither yes nor no..)

This is discussed in depth in RFC1191 and W. Richard Stevens' book "TCP/IP Illustrated Volume 1" (see page 29-31). Aron