1. Verify authentication has completed
2. Verify DHCP client service is running
3. Verify that the encryption level is correct between the client and access point

Network Wireless troubleshootingNetwork Wireless troubleshooting

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Determining the current MTU

The MTU or Maximum Transmission Unit of a given connection varies depending on different factors of the connection.

The important thing to remember is that the MTU is different from the MSS (Maximum Segment Size) of a frame that is sent across a particular connection.

The MTU is the complete Frame including all Headers (TCP/IP)

The MSS is the Maximum amount of Data excluding all Headers:

• MTU is 1500 - 20 bytes for TCP - 20 bytes for IP = MSS 1460

10/100/1000 Ethernet default to 1500, yet this can be modified via registry.

(1000 Ethernet has a feature called Jumbo Frames that can increase frame sizes to 64k, yet their MTU is still ‘defined’ at 1500)

Other forms of connections can be less or more:

• PPP Connections will be less.
• PPTP/L2TP/IPSec/Wireless connections can have 1500 byte MTU’s yet their MSS is smaller due to the number of headers and the size thereof.

To determine the current MTU of the existing connection, the following tests can be performed:

• Use the PING Command with the -f switch to localhost:
  • ping -f -l 1493 localhost
  • ping -f -l 1492 localhost

When Pinging LocalHost, 8 Bytes of Data are ICMP data, leaving us with an MTU of 1500 Bytes.

Testing MTU Issues with Ping.exe

MTU’s are a frequent issue when dealing with cross segment communication. If a Device sends a frame of a particular size, and the Intermediate Hardware does not pass frames larger than a set amount, communication can appear unstable.

A common test that can be used is to try and ‘ping’ remote devices using specific command line switches to verify whether the devices in between will allow the Frames of a particular size to go through.

Using ping with the following switches accommodates this:

• PING -f -l 1472 <Remote Host>

The -f Switch tells any device the receives the Frame not to Fragment the Frame into separate pieces for transmission.

The -l 1472 Switch tells Ping to use 1472 Bytes of data

(20 bytes for IP - 8 bytes for ICMP)

If ping returns:

• Packet needs to be fragmented but DF set.

This implies that a device in between recognized that the frame was too large and requested it to be Fragmented.

If Ping returns:

• Request Timed Out

This implies that the frame was unable to get to its destination, or the response was unable to return.

If this occurs try a regular ping:

• PING <Remote Host>

And if this works and returns:

• Reply from XXX

Then you are inevitably dealing with an MTU Problem.

If ping ALWAYS returns:

• Request Timed Out

Then ICMP may be blocked as a protocol, and is therefore not able to be valued as a valid testing tool.

Changing MTU w/out Reboot

If PING does not work successfully as a testing tool to confirm that communication works with higher MTU values. A method exists to modify the MTU of the specific Network Adapter and then reproduce the behavior that is causing the issue.

Perform the Following Steps to modify the MTU:

• Open Regedit.exe.
• Open the following Registry key:
  • HKLM\System\CCS\Services\TCPIP\Parameters\Interfaces
• Start looking through the list of GUID Keys under Interfaces to find the Adapter of interest. (Use IPAddress, to find match)
• Once identified, add a REG_DWORD value to this Key called “MTU”.
• Set the value to 576 Decimal (0×240 Hex)
• Close Regedit.
• Open Control Panel
• Open Network Connections
• Find the Connectoid that matches the Network Adapter of interest.
• Highlight the Connectoid with the Mouse and Click your right Mouse Button.
• Choose Disable from the Menu.
• After a brief moment, the Connectoid will display the word “Disabled” next to it.
• Highlight the Connectoid with the Mouse and Click your right Mouse Button.
• Choose Enable from the Menu.
• After a brief moment, the Connectoid will display the word “Enabled” next to it.
• By disabling and re-enabling the adapter, the MTU Defined in the registry should be implemented on the Adapter.
• Run through the set of steps to reproduce the problem and see if this issue still exists.
• If not, you may have identified cause.
• This step set the MTU to a much lower value than may be recommended for some environments. Discuss the issue with the customer to determine if the MTU can be more optimally configured.

MTU settings NetworkMTU settings Network

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How to detect Misconfigured TCPIP Configuration

Running IPConfig.exe
• From a Command Prompt, run the command “IPCONFIG /ALL”
• If the Output from the customer returns an error, then there is a more serious Networking issue.

Checking for Multihomed Settings
If the Output from the IPCONFIG /ALL shows:
1. Multiple network Adapters installed
2. Multiple IP Addresses for any Adapter

Then the system is considered Multihomed. As such, the system may be performing as designed, yet causing problems with applications or components that are not Multihome-aware.
Refer to the following KB Articles to determine whether any of the issues may relate to the problems being experienced.

• You cannot transfer files from a multihomed computer to another Windows Messenger user by using Windows Messenger 5.0 - http://support.microsoft.com/default.aspx?scid=KB;EN-US;835972
• How to troubleshoot event ID 8032 and 8021 messages on master browsers - http://support.microsoft.com/default.aspx?scid=KB;EN-US;833441
• Clients cannot log on to domain controllers that are Windows Server 2003-based DNS servers, and network interfaces that are not registered in DNS can still perform dynamic updates - http://support.microsoft.com/default.aspx?scid=KB;EN-US;832478
• Group Policy Settings Do Not Apply to a Client Computer That Is Multihomed - http://support.microsoft.com/default.aspx?scid=KB;EN-US;830513
• Name resolution and connectivity issues occur on Windows 2000 domain controllers that have the Routing and Remote Access service and DNS installed - http://support.microsoft.com/default.aspx?scid=KB;EN-US;830063
• An IP multicast may not be sent correctly from Windows 2000, Windows XP, or Windows Server 2003 - http://support.microsoft.com/default.aspx?scid=KB;EN-US;827536

Checking for Redundant Gateways

If the Output from the IPCONFIG /ALL shows:
1. Multiple Default Gateways on any one Adapter installed
2. A separate Default Gateway IP Address on each of multiple Adapters
Then the system is using Redundant Default Gateways. As such, the system may be performing as designed, yet there may be some performance or connectivity issues with applications or components that are not designed to communicate properly using the Default Gateway mechanism in place.
The Default Gateway strategy for redundant Default Gateways is known as Dead-Gateway Detection. Details on this implementation are available at the following locations:
• Default Gateway Behavior for Windows TCP/IP -http://www.microsoft.com/technet/community/columns/cableguy/cg0903.mspx
• Microsoft Windows Server 2003 TCP/IP Implementation Details - http://www.microsoft.com/downloads/details.aspx?FamilyID=06c60bfe-4d37-4f50-8587-8b68d32fa6ee&DisplayLang=en
Refer to the following KB Articles to determine whether any of the issues may relate to the problems being experienced:
• Multiple Default Gateways Can Cause Connectivity Problems - http://support.microsoft.com/default.aspx?scid=KB;EN-US;159168
• Dead Gateway Detection Does Not Fail Over UDP Traffic to Alternate Gateway - http://support.microsoft.com/default.aspx?scid=KB;EN-US;319778
• Default Gateway Configuration for Multihomed Computers - http://support.microsoft.com/default.aspx?scid=KB;EN-US;157025
• How to use an IP settings test to determine whether a customer has Internet connectivity

NetworkNetwork

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When troubleshooting modem connectivity problems and RAS errors related to hardware & modem connectivity problems (errors:

692
Hardware failure in port or attached device.

721
Remote PPP peer is not responding.

734
The PPP link control protocol terminated.) make sure you investigate these items:

1) Driver issue: Verify that you are using the correct and updated modem driver. Or run the add modem wizard and force it to select a “Standard X bps” driver to match the speed of the modem. The modem driver provided by the manufacturer is usually an INF file that adds various setup strings and response codes from the Hayes command set (AT commands) to the registry, and selecting the wrong driver can have negative effects. The Standard modem driver uses a very basic command set.

2) Modem speed: There are 2 different data rates involved with every successful modem connection:

1. Port Speed refers to the speed of the serial COM channel used by the computer to exchange data with modem. Port Speed can be set to a specific rate or to Auto via the Phone and Modems Control Panel. Lowering Port Speed slows the rate that the modem’s internal buffers fill, giving the device more time to push data onto the line, thus reducing packet loss. Lowering this value can sometimes rescue a bad connection by reducing the impact of line speed fluctuations on the quality of the received data.

2. Line, or Connection Speed, refers to the negotiated bandwidth of the modem-to-modem connection across the Telco line. It represents the maximum speed the 2 modems can exchange data in a given direction. Line speed and compression are negotiated by the modems during the connection process (all that whistling and screeching you hear if the speaker is on). Line speed and compression values are dependent on the quality of the entire Telco path at the time a connection is initiated. Both can vary widely during a connection and can be different in each direction. Line speed and compression are displayed in the dialup Connection Status window. These are static values and will not change even though the typical modem can dynamically compensate for line changes. Line speed and compression amount can only be set to specific values using Hayes commands.

Check the connection rate of your modem and try lowering the speed if you are having problems. Modems always connect at a lower bit-per-second (bps) rate than specified. The remote access server may not respond if your modem cannot operate at a higher bps rate. The inability to operate at a higher rate could also be because of the switching equipment between the client and the server or increased static on the phone line.

3) Modem settings: Check the other modem settings (hardware compression vs software compression, data & parity bits, etc)

4) App conflict: Make sure another application isn’t already trying to use the modem (Fax software, PC Anywhere, etc)

5) Different port: Trying plugging the modem into another serial port (Com 3 vs Com 2, etc)

6) New cable: Try another modem cable if available

7) New modem: Try another modem on the client if available (or server if the problem is that nobody can dial the server)
NetworkNetwork

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How to Enable Tracing with Netsh

You can use the Netsh command to enable and disable tracing for specific components or for all components. To enable and disable tracing for a specific component, use the following syntax:

netsh ras set tracing Component enabled|disabled

where Component is a component in the list of components found in the Windows 2000 registry under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing.

To enable tracing for all components the command is

netsh ras set tracing * enabled

Here is a list of useful components to enable for tracing for EAP-TLS authentications and corresponding netsh commands:

IASHLPR (the Iashlpr.log file in the SystemRoot\tracing folder)

netsh ras set tracing iashlpr enabled

IASPIPE (the Iaspipe.log file in the SystemRoot\tracing folder)

netsh ras set tracing iaspipe enabled

IASRAD (the Iasrad.log file in the SystemRoot\tracing folder)

netsh ras set tracing iasrad enabled

IASSAM (the Iassam.log file in the SystemRoot\tracing folder)

netsh ras set tracing iassam enabled

IASSDO (the Iassdo.log file in the SystemRoot\tracing folder)

netsh ras set tracing iassdo enabled

IASUSERR (the Iasuserr.log file in the SystemRoot\tracing folder)

netsh ras set tracing iasuserr enabled

RASTLS (the Rastls.log file in the SystemRoot\tracing folder)

netsh ras set tracing rastls enabled

NetworkNetwork

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