FHTC Network Troubleshooting Flowchart

↓
Are the switch, hub, or wireless access point's power & link-lights lit?
Yes or No

↓
ping* the destination by name. Successful?
Yes or No

↓

Possible Solutions

A. Specific service is down on destination server. The server itself is up and communicating, but the specific service you are trying to access is down for some reason. Figure out why the service is down (look at configuration, recent updates, & logs), and bring it back up. If it is still up but not responding, restart it.

B. Misconfigured firewall. Network firewall may be blocking all access from your LAN to specific service port on destination server. Configure it to allow your LAN access to service.

C. Malware infection on destination server or it has been hacked. Scan server for malware infection using anti-malware software such as MalwareBytes. Check for signs of break-in (look at the logs).

If All Else Fails

A. Sniff the network with Wireshark on the server while recreating the problem. See if packets are actually being sent to the correct port and if there are any replies. Look for packets containing diagnostic or error messages.

B. Search the Internet. See if others have had the same problem, and if so, how they solved it.

Problem Solved?
Document Your Solution
FINISHED

↓
ping* the destination by IP address. Successful?
Yes or No

↓

Possible Solutions

A. Name of destination unable to be resolved for one of the following reasons:

i. Name not configured in DNS server. Make sure proper records (A, CNAME, MX, etc) for name are found in DNS zone file on your nameserver.

ii. DNS resolver or nameserver down or locked-up. Verify that your DNS servers are running properly. If not, figure out why and bring them back up.

iii. WINS server down or locked-up. Verify that your WINS servers are running properly. If not, figure out why and bring them back up.

iv. DHCP server is giving out wrong DNS or WINS server addresses. Properly configure DHCP server’s scope to provide correct DNS & WINS server addresses.

Possible Solutions

A. Sniff the network with Wireshark while recreating the problem. Pay special attention to any name resolution packets (DNS, NetBIOS, LLMNR).

Problem Solved?
Document Your Solution
FINISHED

↓
Execute: ipconfig /all
on at least two LAN workstations having the same problem. What type of IP addresses?
DHCP starting with 169.254 (APIPA) or DHCP IP addresses or Static IP addresses

↓

Possible Solutions

A. DHCP server down, not configured properly, or not installed on LAN. Start it back up, configure it properly, or install it.

B. Locked-up switch, hub, or access point. Unplug it and plug it back in. If it is managed and still unresponsive, try resetting it back to factory default settings.

C. Misconfigured managed switch or access point. Configure it properly. If all else fails, reset it to factory default settings.

D. Bad switch, hub, or access point. Power lights are still lit, but link lights probably are not. Swap it with another one to test. Replace if bad.

E. Chatty NIC on LAN. Malfunctioning or faulty NICs sometimes become "chatty", putting out excessive packets on the network and using up all of its bandwidth, which affects all workstations in that broadcast domain. Unplug the power from the computer with the chatty NIC and then plug it back in. If this doesn't fix the problem, the NIC is probably bad, in which case it will have to be replaced or disabled.

Problem Solved?
Document Your Solution
FINISHED

↓
ping* Default Gateway router. Successful?
Yes or No

↓
On which LAN is the destination located?

Same LAN as workstation.

Different LAN on the Internet.

Different LAN, but still on this organization's network.

↓

Possible Solutions

A. Destination down or locked-up. Boot or reboot it. Plug it in first if it is unplugged from power.

B. Bad cable or cable unplugged between destination and switch/hub. If the link-lights are not lit on the destination, this is probably the problem.

C. Misconfigured IP settings on destination. Check its IP settings and correct them if necessary.

D. DHCP server is giving out wrong subnet mask. Properly configure DHCP server’s scope to provide correct subnet mask.

E. Destination’s firewall software is blocking access. Try disabling firewall software on destination. If it fixes problem, reconfigure firewall software to allow access to your LAN.

F. Faulty, disabled, or misconfigured NIC on destination. Verify NIC is enabled and has correct drivers installed. Verify that it is configured for correct speed. Test with loopback or swap with another NIC to see if it is bad.

G. Malware infection on destination server or it has been hacked. Scan server for malware infection using anti-malware software such as MalwareBytes. Check for signs of break-in (look at the logs).

If All Else Fails

A. Sniff the network with Wireshark on the destination while recreating the problem. See if packets are actually arriving at destination. Look for packets containing diagnostic or error messages.

Problem Solved?
Document Your Solution
FINISHED

↓
tracert the destination by IP address. How far did the trace go?

Past the default gateway to other LANs, but not onto the Internet

Past your routers and onto the Internet, but not to the destination.

Not past the default gateway.

↓

Possible Solutions

A. One of the routers between your default gateway and the router connected to the Internet is down, misconfigured, disconnected, or faulty. Restart suspect router. Check link-lights. Check IP configurations. Check cables. Try pinging from the suspect router to the next router.

B. A switch/hub connecting routers to one another is down or locked-up. A switch/hub connecting routers to one another is down or locked-up.

Problem Solved?
Document Your Solution
FINISHED

↓

Possible Solutions

A. Destination server is down. Wait patiently for it to come back up, or contact the company that owns it and inform them that it is down. Try http://isup.me to see if the server is down for everybody on the Internet, not just you.

B. Your internet connection (T1, DSL, cable, etc.) is down. If the trace stops after your router that connects to the Internet, and that router seems to be functioning properly, call your ISP.

C. A router on the Internet is down. Wait patiently for it to come back up.

Problem Solved?
Document Your Solution
FINISHED

↓

Possible Solutions

A. Default gateway router’s outgoing interface is disconnected, disabled, misconfigured, or faulty. Check its link-light. Check its IP configuration. Try pinging from the router itself to the next router.

B. The switch/hub connected to the outgoing interface of the default gateway router is down or locked-up. Check the power & link-lights on that switch/hub.

C. DHCP server is giving out wrong subnet mask. This could make the workstations think the destination is on the same LAN, when it is really on a different one. Properly configure DHCP server’s scope to provide correct subnet mask.

D. IP conflict with default gateway. Another PC on the LAN is using the same IP address as the default gateway. Correct it.

Problem Solved?
Document Your Solution
FINISHED

↓
tracert the destination by IP address. How far did the trace go?

Past the local router, but not all the way to the destination LAN.

Not past the local router.

All the way to the destination LAN, but no response from destination.

↓
This could make the workstations think the destination is on the same LAN, when it is really on a different one. Properly configure DHCP server’s scope to provide correct subnet mask.

Possible Solutions

A. Default gateway router’s outgoing interface is disconnected, disabled, misconfigured, or faulty. Check its link-light. Check its IP configuration. Try pinging from the router itself to the next router.

B. The switch/hub connected to the outgoing interface of the default gateway router is down or locked-up. Check the power & link-lights on that switch/hub.

C. DHCP server is giving out wrong subnet mask.
D. IP conflict with default gateway. Another PC on the LAN is using the same IP address as the default gateway. Correct it.

Problem Solved?
Document Your Solution
FINISHED

↓

Possible Solutions

A. Destination down or locked-up. Boot or reboot it. Plug it in first if it is unplugged from power.

B. Bad cable or cable unplugged between destination and switch/hub. If the link-lights are not lit on the destination, this is probably the problem.

C. Misconfigured IP settings on destination. Check its IP settings and correct them if necessary.

D. Destination’s firewall software is blocking access. Try disabling firewall software on destination. If it fixes problem, reconfigure firewall software to allow access to your LAN.

E. Faulty, disabled, or misconfigured NIC on destination. Verify NIC is enabled and has correct drivers installed. Verify that it is configured for correct speed. Test with loopback or swap with another NIC to see if it is bad.

F. Malware infection on destination server or it has been hacked. Scan server for malware infection using anti-malware software such as MalwareBytes. Check for signs of break-in (look at the logs).

G. IP conflict. Another PC on the destination LAN is using the same IP address as the destination or its default gateway. Correct it.

If All Else Fails

A. Sniff the network with Wireshark on the destination while recreating the problem. See if packets are actually arriving at destination. Look for packets containing diagnostic or error messages.

Problem Solved?
Document Your Solution
FINISHED

↓
Are the router’s power & link-lights lit?
Yes or No

↓

Possible Solutions

A. Misconfigured router. The router may be configured with the wrong IP addresses for its interfaces. Configure them properly.

B. Rogue DHCP server giving out wrong IP addresses. If addresses are from DHCP, verify that they are from the correct IP network for this subnet. If not, there could be a rogue DHCP server dishing out incorrect addresses. Find it and shut it down.

C. DHCP server is giving out wrong default gateway address. Properly configure DHCP server’s scope to provide correct default gateway router IP address.

D. Router is on a different switch/hub, and that switch/hub is down or locked-up. Power-on or reset switch/hub.

Problem Solved?
Document Your Solution
FINISHED

↓

Possible Solutions

A. Power unplugged from router. Plug it in.

B. Bad cable or cable unplugged between router and switch, hub, or access point. If the link-lights are not lit on the router, this is probably the problem.

C. Locked-up router. Unplug it and plug it back in. If it is still unresponsive, you may have to reset it back to factory default settings.

D. Bad router. Swap it with another one to test. Replace if bad.

Problem Solved?
Document Your Solution
FINISHED

↓
ping* other computers on the same LAN. Successful?
Yes or No

↓

Possible Solutions

A. Locked-up switch, hub, or access point. Unplug it and plug it back in. If it is managed and still unresponsive, try resetting it back to factory default settings.

B. Misconfigured managed switch or access point. Configure it properly. If all else fails, reset it to factory default settings.

C. Bad switch, hub, or access point. Power lights are still lit, but link lights probably are not. Swap it with another one to test. Replace if bad.

D. Chatty NIC on LAN. Malfunctioning or faulty NICs sometimes become "chatty", putting out excessive packets on the network and using up all of its bandwidth, which affects all workstations in that broadcast domain. Unplug the power from the computer with the chatty NIC and then plug it back in. If this doesn't fix the problem, the NIC is probably bad, in which case it will have to be replaced or disabled.

Problem Solved?
Document Your Solution
FINISHED

↓

Possible Solutions

A. Power unplugged from switch, hub, or access point. Plug it in.

B. Locked-up switch, hub, or access point. Unplug it and plug it back in. If it is managed and still unresponsive, try resetting it back to factory default settings.

C. Bad switch, hub, or access point. Swap it with another one to test. Replace if bad.

Problem Solved?
Document Your Solution
FINISHED

↓
Restart the affected workstation. Problem solved?
Yes or No

↓
Problem Solved
Document Your Solution
FINISHED

↓
Is the Link-Light on the NIC lit?
Yes or No

↓
Execute: ipconfig /all
What type of IP address?
No IP address or Valid Static or DHCP or DHCP starting with 169.254 (APIPA)

↓

Possible Solutions

A. NIC driver not installed or wrong NIC driver installed. Install or update NIC driver in Device Manager.

B. Faulty NIC. Try a different NIC in the workstation.

Problem Solved?
Document Your Solution
FINISHED

↓
ping* the destination by name. Successful?
Yes or No

↓

Possible Solutions

A. Faulty application software. Check app’s settings. Try reinstalling app. Check app manufacturer’s website. If it is a web browser, clear the cache & check the proxy settings.

B. Misconfigured firewall. Disable Windows firewall. Check with admin of network firewall to see if workstation is being blocked.

C. Invalid entry for destination name in
\windows\system32\drivers\etc\hosts file. It normally should not be listed in this file at all.

D. Insufficient rights to access service. Check with admin of service or the server itself to see if user has sufficient rights or their account has been disabled.

E. User is using incorrect username and/or password.

F. Malware infection. Scan system for malware infection using anti-malware software such as MalwareBytes.

If All Else Fails

A. Sniff the network with Wireshark while recreating the problem. See if packets are actually being sent to the correct addresses and if there are any replies.

B. Search the Internet. See if others have had the same problem, and if so, how they solved it.

Problem Solved?
Document Your Solution
FINISHED

↓
ping* the destination by IP address. Successful?
Yes or No

↓

Possible Solutions

A. Incorrect DNS server or WINS server address. Compare these addresses with the settings on another workstation that is working on the LAN.

B. Invalid entry for destination name in
\windows\system32\drivers\etc\hosts file. It normally should not be listed in this file at all.

If All Else Fails

A. Sniff the network with Wireshark while recreating the problem. See if packets are actually being sent to the correct addresses and if there are any replies. Pay special attention to any name resolution packets (DNS, NetBIOS, LLMNR).

Problem Solved?
Document Your Solution
FINISHED

↓
ping* the default gateway’s IP address. Successful?
Yes or No

↓
View it using the route print command, and compare it with the routing table on another workstation that is working on the LAN.

Possible Solutions

A. Incorrect IP address or subnet mask. Compare with the settings on another workstation that is working on the LAN.

B. Incorrect, outdated, or misconfigured NIC driver. Verify NIC driver in Device Manager, and don’t forget to check the NIC’s settings, such as connection speed.

C. Malware infection. Scan system for malware infection using anti-malware software such as MalwareBytes.

D. Reset Windows TCP/IP stack using
netsh int ip reset command. Reboot after executing command and reconfigure the NIC’s IP settings.

E. Faulty cable. Test with cable tester or swap cables. Sometimes link-lights lie. Make sure cable is not too long.

F. If Wireless, lost connection to access point. Make sure workstation is close enough to access point. Check for interference. Make sure wireless NIC is configured with correct SSID & passphrase.

G. Faulty NIC. Try a different NIC in the workstation.

H. Bad entry in local routing table.
I. IP conflict. Another PC on the LAN is using the same IP address as yours. Correct it.

When All Else Fails

A. Sniff the network with Wireshark while recreating the problem. See if packets are actually being sent to the correct addresses and if there are any replies.

B. Search the Internet. See if others have had the same problem, and if so, how they solved it.

Problem Solved?
Document Your Solution
FINISHED

↓

Possible Solutions

A. Incorrect subnet mask or default gateway. Compare with the settings on another workstation that is working on the LAN.

B. Bad entry in local routing table. View it using the route print command, and compare it with the routing table on another workstation that is working on the LAN.

C. Misconfigured firewall. Disable Windows firewall. Check with admin of network firewall to see if workstation is being blocked.

If All Else Fails

A. Sniff the network with Wireshark while recreating the problem. See if packets are actually being sent to the correct addresses and if there are any replies.

Problem Solved?
Document Your Solution
FINISHED

↓

Possible Solutions

A. Incorrect, outdated, or misconfigured NIC driver. Verify NIC driver in Device Manager, and don’t forget to check the NIC’s settings, such as connection speed.

B. Malware infection. Scan system for malware infection using anti-malware software such as MalwareBytes.

C. Faulty cable. Test with cable tester or swap cables. Sometimes link-lights lie. Make sure cable is not too long.

D. If Wireless, lost connection to access point. Make sure workstation is close enough to access point. Check for interference. Make sure wireless NIC is configured with correct SSID & passphrase.

E. Faulty NIC. Try a different NIC in the workstation.

F. Reset Windows TCP/IP stack using
netsh int ip reset command. Reboot after executing command and reconfigure the NIC’s IP settings.

Problem Solved?
Document Your Solution
FINISHED

↓

Possible Solutions

A. Cable unplugged from NIC or switch/hub. Plug it in.

B. Faulty cable. Test with cable tester or swap cables.

C. Faulty or disabled NIC. Check if it is enabled in Windows and BIOS setup. Test with loopback. Swap with another NIC.

D. Bad port or uplink port on switch/hub. Move the cable to a different port.

E. Disabled port on managed switch. Login to switch and enable port.

F. If Wireless, lost connection to access point. Make sure workstation is close enough to access point. Check for interference. Make sure wireless NIC is configured with correct SSID & passphrase.

Problem Solved?
Document Your Solution
FINISHED

Gather Clues
A.	Ask Questions. i. What were you doing when the problem occurred? ii. Have there been any recent changes to the network?
B.	Have the customer recreate the problem while you watch. While watching, check for obvious user errors (ID10T errors), such as Caps-Lock being on.

Possible Solutions
A.	Specific service is down on destination server. The server itself is up and communicating, but the specific service you are trying to access is down for some reason. Figure out why the service is down (look at configuration, recent updates, & logs), and bring it back up. If it is still up but not responding, restart it.
B.	Misconfigured firewall. Network firewall may be blocking all access from your LAN to specific service port on destination server. Configure it to allow your LAN access to service.
C.	Malware infection on destination server or it has been hacked. Scan server for malware infection using anti-malware software such as MalwareBytes. Check for signs of break-in (look at the logs).
If All Else Fails
A.	Sniff the network with Wireshark on the server while recreating the problem. See if packets are actually being sent to the correct port and if there are any replies. Look for packets containing diagnostic or error messages.
B.	Search the Internet. See if others have had the same problem, and if so, how they solved it.

Possible Solutions
A.	Name of destination unable to be resolved for one of the following reasons:
	i.	Name not configured in DNS server. Make sure proper records (A, CNAME, MX, etc) for name are found in DNS zone file on your nameserver.
	ii.	DNS resolver or nameserver down or locked-up. Verify that your DNS servers are running properly. If not, figure out why and bring them back up.
	iii.	WINS server down or locked-up. Verify that your WINS servers are running properly. If not, figure out why and bring them back up.
	iv.	DHCP server is giving out wrong DNS or WINS server addresses. Properly configure DHCP server’s scope to provide correct DNS & WINS server addresses.
Possible Solutions
A.	Sniff the network with Wireshark while recreating the problem. Pay special attention to any name resolution packets (DNS, NetBIOS, LLMNR).

Possible Solutions
A.	DHCP server down, not configured properly, or not installed on LAN. Start it back up, configure it properly, or install it.
B.	Locked-up switch, hub, or access point. Unplug it and plug it back in. If it is managed and still unresponsive, try resetting it back to factory default settings.
C.	Misconfigured managed switch or access point. Configure it properly. If all else fails, reset it to factory default settings.
D.	Bad switch, hub, or access point. Power lights are still lit, but link lights probably are not. Swap it with another one to test. Replace if bad.
E.	Chatty NIC on LAN. Malfunctioning or faulty NICs sometimes become "chatty", putting out excessive packets on the network and using up all of its bandwidth, which affects all workstations in that broadcast domain. Unplug the power from the computer with the chatty NIC and then plug it back in. If this doesn't fix the problem, the NIC is probably bad, in which case it will have to be replaced or disabled.

Possible Solutions
A.	Destination down or locked-up. Boot or reboot it. Plug it in first if it is unplugged from power.
B.	Bad cable or cable unplugged between destination and switch/hub. If the link-lights are not lit on the destination, this is probably the problem.
C.	Misconfigured IP settings on destination. Check its IP settings and correct them if necessary.
D.	DHCP server is giving out wrong subnet mask. Properly configure DHCP server’s scope to provide correct subnet mask.
E.	Destination’s firewall software is blocking access. Try disabling firewall software on destination. If it fixes problem, reconfigure firewall software to allow access to your LAN.
F.	Faulty, disabled, or misconfigured NIC on destination. Verify NIC is enabled and has correct drivers installed. Verify that it is configured for correct speed. Test with loopback or swap with another NIC to see if it is bad.
G.	Malware infection on destination server or it has been hacked. Scan server for malware infection using anti-malware software such as MalwareBytes. Check for signs of break-in (look at the logs).
If All Else Fails
A.	Sniff the network with Wireshark on the destination while recreating the problem. See if packets are actually arriving at destination. Look for packets containing diagnostic or error messages.

Possible Solutions
A.	One of the routers between your default gateway and the router connected to the Internet is down, misconfigured, disconnected, or faulty. Restart suspect router. Check link-lights. Check IP configurations. Check cables. Try pinging from the suspect router to the next router.
B.	A switch/hub connecting routers to one another is down or locked-up. A switch/hub connecting routers to one another is down or locked-up.

Possible Solutions
A.	Destination server is down. Wait patiently for it to come back up, or contact the company that owns it and inform them that it is down. Try http://isup.me to see if the server is down for everybody on the Internet, not just you.
B.	Your internet connection (T1, DSL, cable, etc.) is down. If the trace stops after your router that connects to the Internet, and that router seems to be functioning properly, call your ISP.
C.	A router on the Internet is down. Wait patiently for it to come back up.

Possible Solutions
A.	Default gateway router’s outgoing interface is disconnected, disabled, misconfigured, or faulty. Check its link-light. Check its IP configuration. Try pinging from the router itself to the next router.
B.	The switch/hub connected to the outgoing interface of the default gateway router is down or locked-up. Check the power & link-lights on that switch/hub.
C.	DHCP server is giving out wrong subnet mask. This could make the workstations think the destination is on the same LAN, when it is really on a different one. Properly configure DHCP server’s scope to provide correct subnet mask.
D.	IP conflict with default gateway. Another PC on the LAN is using the same IP address as the default gateway. Correct it.

Possible Solutions
A.	Misconfigured router. The router may be configured with the wrong IP addresses for its interfaces. Configure them properly.
B.	Rogue DHCP server giving out wrong IP addresses. If addresses are from DHCP, verify that they are from the correct IP network for this subnet. If not, there could be a rogue DHCP server dishing out incorrect addresses. Find it and shut it down.
C.	DHCP server is giving out wrong default gateway address. Properly configure DHCP server’s scope to provide correct default gateway router IP address.
D.	Router is on a different switch/hub, and that switch/hub is down or locked-up. Power-on or reset switch/hub.

Possible Solutions
A.	Power unplugged from router. Plug it in.
B.	Bad cable or cable unplugged between router and switch, hub, or access point. If the link-lights are not lit on the router, this is probably the problem.
C.	Locked-up router. Unplug it and plug it back in. If it is still unresponsive, you may have to reset it back to factory default settings.
D.	Bad router. Swap it with another one to test. Replace if bad.

Possible Solutions
A.	Power unplugged from switch, hub, or access point. Plug it in.
B.	Locked-up switch, hub, or access point. Unplug it and plug it back in. If it is managed and still unresponsive, try resetting it back to factory default settings.
C.	Bad switch, hub, or access point. Swap it with another one to test. Replace if bad.

Possible Solutions
A.	NIC driver not installed or wrong NIC driver installed. Install or update NIC driver in Device Manager.
B.	Faulty NIC. Try a different NIC in the workstation.

Possible Solutions
A.	Faulty application software. Check app’s settings. Try reinstalling app. Check app manufacturer’s website. If it is a web browser, clear the cache & check the proxy settings.
B.	Misconfigured firewall. Disable Windows firewall. Check with admin of network firewall to see if workstation is being blocked.
C.	Invalid entry for destination name in \windows\system32\drivers\etc\hosts file. It normally should not be listed in this file at all.
D.	Insufficient rights to access service. Check with admin of service or the server itself to see if user has sufficient rights or their account has been disabled.
E.	User is using incorrect username and/or password.
F.	Malware infection. Scan system for malware infection using anti-malware software such as MalwareBytes.
If All Else Fails
A.	Sniff the network with Wireshark while recreating the problem. See if packets are actually being sent to the correct addresses and if there are any replies.
B.	Search the Internet. See if others have had the same problem, and if so, how they solved it.

Possible Solutions
A.	Incorrect DNS server or WINS server address. Compare these addresses with the settings on another workstation that is working on the LAN.
B.	Invalid entry for destination name in \windows\system32\drivers\etc\hosts file. It normally should not be listed in this file at all.
If All Else Fails
A.	Sniff the network with Wireshark while recreating the problem. See if packets are actually being sent to the correct addresses and if there are any replies. Pay special attention to any name resolution packets (DNS, NetBIOS, LLMNR).

Possible Solutions
A.	Incorrect IP address or subnet mask. Compare with the settings on another workstation that is working on the LAN.
B.	Incorrect, outdated, or misconfigured NIC driver. Verify NIC driver in Device Manager, and don’t forget to check the NIC’s settings, such as connection speed.
C.	Malware infection. Scan system for malware infection using anti-malware software such as MalwareBytes.
D.	Reset Windows TCP/IP stack using netsh int ip reset command. Reboot after executing command and reconfigure the NIC’s IP settings.
E.	Faulty cable. Test with cable tester or swap cables. Sometimes link-lights lie. Make sure cable is not too long.
F.	If Wireless, lost connection to access point. Make sure workstation is close enough to access point. Check for interference. Make sure wireless NIC is configured with correct SSID & passphrase.
G.	Faulty NIC. Try a different NIC in the workstation.
H.	Bad entry in local routing table.
I.	IP conflict. Another PC on the LAN is using the same IP address as yours. Correct it.
When All Else Fails
A.	Sniff the network with Wireshark while recreating the problem. See if packets are actually being sent to the correct addresses and if there are any replies.
B.	Search the Internet. See if others have had the same problem, and if so, how they solved it.

Possible Solutions
A.	Incorrect subnet mask or default gateway. Compare with the settings on another workstation that is working on the LAN.
B.	Bad entry in local routing table. View it using the route print command, and compare it with the routing table on another workstation that is working on the LAN.
C.	Misconfigured firewall. Disable Windows firewall. Check with admin of network firewall to see if workstation is being blocked.
If All Else Fails
A.	Sniff the network with Wireshark while recreating the problem. See if packets are actually being sent to the correct addresses and if there are any replies.

Possible Solutions
A.	Cable unplugged from NIC or switch/hub. Plug it in.
B.	Faulty cable. Test with cable tester or swap cables.
C.	Faulty or disabled NIC. Check if it is enabled in Windows and BIOS setup. Test with loopback. Swap with another NIC.
D.	Bad port or uplink port on switch/hub. Move the cable to a different port.
E.	Disabled port on managed switch. Login to switch and enable port.
F.	If Wireless, lost connection to access point. Make sure workstation is close enough to access point. Check for interference. Make sure wireless NIC is configured with correct SSID & passphrase.