Re: Apparent MTU Problem
From: Bryan E. Martin (support_at_ziggycom.net)
Date: 02/25/05
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Date: Fri, 25 Feb 2005 11:11:10 -0600
If no one can help me with this problem, could someone suggest a more
appropriate newsgroup?
Thanks,
Bryan
"Bryan E. Martin" <support@ziggycom.net> wrote in message
news:uI53iUrGFHA.3352@TK2MSFTNGP10.phx.gbl...
> I'll try to make this short and sweet.
>
> I have a Windows Server 2003 Web Edition computer that I am running
> Ipswitch IMail Server 8.15 on. Our dial-up customers are located in a
> colo facility in another city. Until recently, this e-mail server was
> located in my office and customers had to go out over the public internet
> to retrieve their e-mail. A few weeks ago, I moved the e-mail server to
> the colo facility, so now the access servers and e-mail server are on the
> same Ethernet switch.
>
> I have had no problems for 3 1/2 years using the e-mail server in the
> former setup. However, now that the dial-up customers are on the same
> Ethernet switch as the e-mail server, the e-mail is much slower and
> customers who are trying to download large attachments cannot do so.
>
> On the client side, Outlook Express downloads all messages up to the large
> one, and then you see dial-up connection status lights in the system tray
> quit blinking. Eventually Outlook Express pops up a box and says that the
> POP3 server has been idle for 60 seconds, and asks if you want to wait or
> stop. Clicking Wait does no good, it will never download past that point.
>
> On the server side, using Ethereal (a packet logger), I have noticed
> several things. First off, things obviously work smoothly until OE
> attempts to retrieve the large message. When OE sends the command to
> retrieve the large e-mail, things rapidly deteriorate. I start seeing
> alot of duplicate ACKs coming from the client side. Some packets are
> never ACKed, and some ACKS come up to 5-10 seconds, and out of order. All
> this time, though, the server is still attempting to send packets to the
> client, but as I said, the lights aren't even blinking on the client side.
>
> The packets the server is sending are 1514 bytes. (Ethereal says 1514
> bytes captured off the wire, but in the IP section it says the header is
> 20 bytes and the total length is 1500 bytes.) Everything doesn't add up,
> but whatever, I'm no whiz, I'm just reporting what I found. My dial-up
> customers' MTUs are set to 1500 bytes. I am able to ping the mail server
> from a client machine (ping mail.ziggycom.net -f -l 1472) with no problem.
> I started experimenting with the MTU in the registry, restarting each time
> and trying to download mail to my laptop. Finally, at a setting of 1458
> on the NIC card, I was able to download large attachments to my laptop.
> (1478 + 28 = 1472, see above. ??? I just know it worked.) However, this
> has not fixed the problem for everybody and a lot of people are still
> having problems.
>
> HELP!
>
> Thanks,
> Bryan E. Martin
> Ziggycom Online, Inc.
>
- Next message: Michael Giorgio - MS MVP: "Re: This one has me completely baffled with RAS and Messenger"
- Previous message: Tanu Mutreja [MSFT]: "TechChat: DHCP Server & Client Technology, Mar 03, 2005 (10:00 - 11:00 A.M. Pacific Time)."
- In reply to: Bryan E. Martin: "Apparent MTU Problem"
- Messages sorted by: [ date ] [ thread ]
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