As it turns out one of our upstream ISPs has misconfigured a router and there was an MTU issue.
Daniel was correct to guess that it was a "Black Hole Router". My understanding is that basically it's what happens when a router simply discards packets larger than it's MTU size, rather than responding with the proper error code to let the server know to fragment the packets and retransmit. Since the packets just get dropped, the server keeps transmitting the over-large packets until it times out the connection. It was only happening to some domains because the router in question was enough hops away from us that only certain domains were sent that way -- others like SWNYK.COM didn't go through that router and so they weren't affected. The ISP realized their problem late in the day and by 17:30 all of our mail was flowing normally again. -Ben- Ben M. Schorr, MVP-Outlook, CNA, MCPx3 Director of Information Services Damon Key Leong Kupchak Hastert http://www.hawaiilawyer.com > -----Original Message----- > From: Roger Seielstad [mailto:[EMAIL PROTECTED]] > Sent: Wednesday, March 20, 2002 3:00 AM > To: Exchange Discussions > Subject: RE: Some "Hosts Unreachable" > > > First guess, Ben, is that they are set to deny relaying, but > I would guess incorrrectly. > > IIRC, that's RFC compliant behavior for denying relaying - as > long as it tanks before giving a valid response to the 354 section. > > Roger > ------------------------------------------------------ > Roger D. Seielstad - MCSE > Sr. Systems Administrator > Peregrine Systems > Atlanta, GA > > > > -----Original Message----- > > From: Ben Schorr [mailto:[EMAIL PROTECTED]] > > Sent: Tuesday, March 19, 2002 6:00 PM > > To: Exchange Discussions > > Subject: Some "Hosts Unreachable" > > > > > > This is a new one on me; maybe some of you have seen it > > before. Exchange 5.5 on NT4SP6a using the IMS to connect > > through an ISA server. On a handful of hosts the message > > queues up with a "Host Unreachable" error. On most hosts > > (including old favorites like aol.com, hotmail.com, etc.) > > mail comes and goes just fine and we don't seem to be having > > any problems RECEIVING mail. > > > > But to this small band of hosts (including hawaii.edu and > > hawaii.rr.com) the mail just queues up. Here's a snippet > > from an SMTP log that may shed some > > light: > > > > 3/19/02 12:15:06 PM : >>> MAIL > > FROM:<[EMAIL PROTECTED]> SIZE=1977 RET=FULL > > 3/19/02 12:15:06 PM : <<< IO: |250 2.1.0 > > [EMAIL PROTECTED] OK > > | > > 3/19/02 12:15:06 PM : <<< 250 2.1.0 > > [EMAIL PROTECTED] OK > > 3/19/02 12:15:06 PM : >>> RCPT TO:<[EMAIL PROTECTED]> > > NOTIFY=FAILURE,DELAY > > > > 3/19/02 12:15:06 PM : <<< IO: |250 2.1.5 [EMAIL PROTECTED] > > | > > 3/19/02 12:15:06 PM : <<< 250 2.1.5 [EMAIL PROTECTED] > > 3/19/02 12:15:06 PM : >>> DATA > > > > 3/19/02 12:15:06 PM : <<< IO: |354 Start mail input; > > end with <CRLF>.<CRLF> > > | > > 3/19/02 12:15:06 PM : <<< 354 Start mail input; end > > with <CRLF>.<CRLF> > > 3/19/02 12:16:22 PM : 499 Host unreachable: cta.net. Message > > subject: ""Plain Text Test"". Rescheduling delivery for later. > > > > Notice that it seems to be going fine until it gets the 354 > > message, then it sits for a little over a minute and seems to > > time out. This particular test message was just a couple of > > lines of plain text; so it shouldn't be a size issue. > > > > We've already restarted the IMS several times and the entire > > Exchange server once. Judging by the oldest message in the > > queue this problem seems to have started this weekend and no > > unusual system maintenance or changes occurred over the > > weekend. As far as I know we were able to send mail to/from > > those domains just fine on Friday. > > > > Baffling. Any thoughts on what might be causing this and how > > we can resolve it? > > > > -Ben- > > Ben M. Schorr, MVP-Outlook, CNA, MCPx3 > > Director of Information Services > > Damon Key Leong Kupchak Hastert > > http://www.hawaiilawyer.com <http://www.hawaiilawyer.com> > > > > > > _________________________________________________________________ > > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > > Archives: http://www.swynk.com/sitesearch/search.asp > > To unsubscribe: mailto:[EMAIL PROTECTED] > > Exchange List admin: [EMAIL PROTECTED] > > > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Archives: http://www.swynk.com/sitesearch/search.asp > To unsubscribe: mailto:[EMAIL PROTECTED] > Exchange List admin: [EMAIL PROTECTED] > _________________________________________________________________ List posting FAQ: http://www.swinc.com/resource/exch_faq.htm Archives: http://www.swynk.com/sitesearch/search.asp To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED]
