Re: POP3 Connector Issue

From: Chris Puckett [MSFT] (cpuckett_at_online.microsoft.com)
Date: 03/18/04 

Date: Thu, 18 Mar 2004 14:43:17 GMT

We have seen these events caused by mismatched MTU's. In some cases it can
resolved by adjusting the MTU on the router used to connect to the internet
or in other cases you can modify the MTU on the server.

As a test, try running the following command. You can replace the pop
server name with the ones that you receive the events connecting to.

ping -f -l 1472 mail.smcusa.biz

See if this pings or returns "packet needs to be fragmented but DF set".
If it returns the second message, then adjust the 1472 value down (in
increments of 10 for instance) until you find the largest value that pings.
 If you can ping through with 1472, then the MTU is not likely to be the
cause. However, you can still check the MTU value in the registry of the
server to see if it has been set to a value higher than 1500. If the MTU
value does not exist in the registry then the server defaults to the MTU
for media you are connecting with which is most likely 1500.

If you receive a request timed out, that server may not respond to pings.
I experienced this when trying to ping pop.earthlink.net.

Once you know the largest value that pings, you can manually set the MTU in
the registry of the server using the following steps:

If you need to do this on your router, please refer to it's documentation
for adjusting/setting the MTU.
                  
1. Click Start, and then click Control Panel.

2. Double-click "Network and Internet Connections", and then click to
   open the Network Connections folder.

3. If more than one network connection is listed, for each connection,
   double-click the connection and then click the Support tab of the
   Status interface that opens. The connection that shows a Default
   Gateway entry is probably the network connection that is used to
   connect to the Internet. Note the name of the connection (for example,
   "Local Area Connection 2").

4. Start Registry Editor (Regedit.exe).

5. Under the HKEY_LOCAL_MACHINE tree, go to the following key:

SYSTEM\CurrentControlSet\Control\Network\{4D36E972-E325-11CE-BFC1-08002BE103
18}\

6. Under that key are one or more keys that have numeric identifiers. Each
of these keys has a Connection subkey. Examine each of the keys that look
like this:

<ID_for_Adapter>\Connection The Name value in the Connection subkey
provides the network connection name that is used in the Network
Connections folder. When you find the one that matches the name that you
found in step 3, make a note of the <ID_for_Adapter> that the network
connection name is under.

7. Return to HKEY_LOCAL_MACHINE, and then locate the following key
SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\<ID_for_Adapte
r> where <ID_for_Adapter> is the number that you noted in step 6. When you
highlight this key, several values appear on the right side of the screen,
including DefaultGateway and EnableDHCP.

8. Right-click the right side of the screen, click New, and then click
DWORD Value. Name the value MTU.

9. Double-click the value so that you can edit the value, change Base to
Decimal, and then enter the largest acceptable MTU size, which is the size
that you identified by using the Ping tests.

10. Quit Registry Editor.

Chris Puckett, MCSE
Microsoft Small Business Server Support

This posting is provided "AS IS" with no warranties, and confers no rights.

Relevant Pages

  • Re: Windows Update
    ... You may need to reduce the MTU ... size of a PPPoE connection to a value of between 1,400 and 1,480 ... for a network connection, double-click the network connection icon, ... Microsoft CSS Online Newsgroup Support ...
    (microsoft.public.windows.server.sbs)
  • Re: Windows Update
    ... Windows Server 2003, for Windows XP, and for Windows 2000 ... You may need to reduce the MTU ... size of a PPPoE connection to a value of between 1,400 and 1,480 ... for a network connection, double-click the network connection icon, ...
    (microsoft.public.windows.server.sbs)
  • Re: POP3 Connector Issue
    ... Ping statistics for 216.119.106.131: ... I entered the MTU value in the Registry of 1452 today and I will see what ... > server name with the ones that you receive the events connecting to. ... If more than one network connection is listed, for each connection, ...
    (microsoft.public.windows.server.sbs)
  • Re: Windows Update
    ... I changed the MTU size to 1470 in the regsitry as this worked, ... ping command now works with a MTU of 1440. ... Click Services tab and select Hide All Microsoft Services and Disable ... size of a PPPoE connection to a value of between 1,400 and 1,480 ...
    (microsoft.public.windows.server.sbs)
  • RE: pop3 errors
    ... you can modify the MTU on the server. ... See if this pings or returns message "packet needs to be fragmented but DF ... If more than one network connection is listed for each connection ... probably the network connection that is used to connect to the Internet. ...
    (microsoft.public.windows.server.sbs)