Messaging, web pages and MTU
If the maximum transfer unit is not well set, you may have problems for sending messages if they exceed a few lines or which have attachments too large. It is also possible that some web pages are inaccessible.
1) The MTU
To detect the value of MTU to apply, post from the problem from a window DOS, run the following command:
ping-f-l [number of bytes] [IP address of your server to another on your network or your router]
for example:
ping-f-l 1400 192.168.2.1
- If you have an answer such as:
Reply from 192.168.2.1: bytes = 1400 time = 5ms TTL = 64
- You can continue the test by increasing the value of the number of bytes until the answer is:
- The packet must be fragmented but DF set.
- So, for example, if a number of bytes of 1473, your packet must be fragmented and that a value of 1472, you have a useful answer is the 1472 value that represents your MTU.
- To change your MTU, you must configure the registry:
Go to
Start>
Run> type "
regedit" +
ok
Under Win9x:
- Scroll to HKEY_LOCAL_MACHINE \ System \ CurrentControlSet \ Services \ Class \ NetTrans
- Within the NetTrans folder, you have several subfolders "0000", "0001", etc.. Find the one that contains *"DriverDesc TCP / IP", where you have to create new value.
- In the right pane, click the right mouse button: new> String Value> Value name: enter MaxMTU; Value data: state (for our case) 1472
- Click OK, close the registry, restart the PC.
Under WinXP:
Administrator mode:
- > HKEY_LOCAL_MACHINE \ System \ CurrentControlSet \ Services \ Tcpip \ Parameters \ Interfaces \
- Search the file (note there may be several that may appear identical) contain the values:
- (Default)
- Address Type
- DefaultGateway
- DefaultGatewayMetric
- DhcpClass IdBin
- DhcpDefaultGateway
- DhcpIPAddress
- DhcpNameServer
- DhcpServer
- DhcpSubnetMask
- DhcpSubnetMaskOpt
- Domain
- EnableDeadGWDetect
- EnableDHCP
- IPAdress
- IPAutoconfigurationAddress
- IPAutoconfigurationMask
- IPAutoconfigurationSeed
- ...
- TCPAllowedPorts
- UDPAllowedPorts
- UseZeroBroadcast]
- In the right pane, click the right mouse button: new> DWORD> Value Name: MTU indicate; Value data: state (for our case) in 1472 by checking Base "decimal"
- Click on OK and close the registry, restart the PC.
2) If you have a router
- I have a router Edimax BR 6104 (G).
- Despite setting the MTU, the problems persisted. It was therefore necessary that I set the MTU of the router.
- Type in the explorer the IP address of the router (eg http://192.168.xx) into the software configuration of the latter,
- Enter the password if any and click "login"
- Click on "General Setup"> "WAN"> (in the case of a PPPoE connection) "More Configuration"
- Under "MTU", indicating a lower value to the registry (eg 1471),
- Click "Apply" and wait for the router is configured,
3) If you have a firewall:
- The firewall may prevent you from displaying web pages and send emails.
- You will need to disable (temporarily) if the options do not allow you to configure it to display the web pages you want, change it or if there is no possibility to send mails!
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