IP Troubleshooting

IP Troubleshooting Tips

One important step in troubleshooting network communications is to verify the IP address, subnet mask, and default gateway settings of each host. Keep in mind the following as you troubleshoot IP:

• All computers must be assigned a unique IP address.
• Hosts on the same physical network should have IP addresses in the same address range.
• The subnet mask value for all computers on the same physical network must be the same.
• Configure the default gateway value to enable internetwork communication.
• The default gateway address must be on the same subnet as the host's IP address.
• You do not need to configure an IP address on a switch for frames to be switched through the switch. To ping to and from a switch or to remotely manage the switch, configure an IP address on the switch.

Listed below are several common symptoms and things to try to correct communication problems.

Problem	Symptoms	Solution
A single host cannot communicate with any other host.	Ping to any other host fails.	Because the problem exists with only one host, troubleshoot the configuration of the host with the problem.
A single host can communicate with all hosts on the same network, but can't communicate with any host on any other network.	Ping to hosts on the same network succeed, ping to hosts on other networks fails.	Verify the default gateway setting of the host with the problem. Because only a single host has the problem, you should be able to assume that the default gateway device is functioning correctly.
	Traceroute on the host times out with only a single entry.
All hosts can communicate within the same network, but cannot communicate with any host outside of the local network.	Ping to hosts on the same network succeed, ping to hosts on other networks fails.	Check for the following: If hosts have an IP address on the 169.254.0.0/16, then APIPA was used to assign the IP address and the default gateway value will be missing. Verify that the DHCP server is up. If DHCP is used to assign IP information to hosts, verify the default gateway setting delivered by the DHCP server. Verify that the default gateway device is up, has a valid connection to all networks, and has routing table information to reach destination networks.
	Traceroute on the host times out with only a single entry.
All hosts cannot communicate with hosts on a specific outside network. Communication with other networks is fine.	Ping to the remote network fails, traceroute on the host times out with only a single entry.	Add a route to the routing table, or configure the gateway of last resort (default route) on the router. The gateway of last resort is also known as the default gateway for the router.
	The routing table on the router does not show the destination network, or the gateway of last resort is not set.
	The routing table has a route to the destination network. Traceroute on the router times out.	Troubleshoot other routers in the path to the destination network. Use traceroute to identify the last responding router and begin troubleshooting there.
All hosts cannot communicate with a specific remote host. Communication with other remote hosts in the same remote network is fine.	Ping to the remote host fails. Traceroute to the remote host indicates no response from the host.	Troubleshoot the configuration of the remote host.
	The routing table shows a route to the destination network (or the gateway of last resort is used).

 

 

Credit: Testout 640-802 CCNA Notes