[EMAIL PROTECTED] wrote:
> For instance: I've seen hosts that you can communicate with just fine > when SMTP pipelining is off, but which wedge up when you turn it on. > Reason? Some router in between is tossing ICMP Frag Needed packets with > an RFC1918 address, which our border router then tosses, breaking Path > MTU Discovery - and pipelining allows enough RCPT TO: in one packet to > tickle the problem.. (Figuring out why this didn't bite during the DATA > phase is left as an exercise for the reader ;) The worst part is that > both ends did exactly what they were supposed to in the face of > what looked like network outages - abort, requeue, and retry. Actually, that's a TCP bug, not an SMTP bug. The transmitting side should be doing blackhole detection to catch this. Lots of stacks don't do this, even though it isn't exactly rocket-science. Small segments get ACKs, big segments don't. Duh, try smaller segments? Anyway, it still proves the point. You can spend hundreds of man-hours devising a series of tests, and then find out that some seemingly unrelated thing is screwing the results. Not to say that it can't be done, but that it's very expensive, and it requires a holistic approach that is beyond the norm. -- Eric A. Hall http://www.ehsco.com/ Internet Core Protocols http://www.oreilly.com/catalog/coreprot/
