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Viewing configuration by using ipconfig /all
When you troubleshoot a TCP/IP networking problem, begin by checking the TCP/IP configuration on the computer that is experiencing the problem. You can use the ipconfig command to get host computer configuration information, including the IP address, subnet mask, and default gateway.
When you use the ipconfig command with the /all option, a detailed configuration report is produced for all interfaces, including any configured serial ports. With ipconfig /all, you can redirect command output to a file and paste the output into other documents. You can also use this output to confirm the TCP/IP configuration of each computer on the network or to further investigate TCP/IP network problems.
For example, if a computer is configured with an IP address that is a duplicate of an existing IP address, the subnet mask appears as 0.0.0.0.
The following example shows the output of the ipconfig /all command on a computer that running Windows XP Professional and is configured to use the DHCP server for automatic TCP/IP configuration, and WINS and DNS servers for name resolution.
IP Configuration Node Type . . . . . . . . . : Hybrid IP Routing Enabled. . . . . : No WINS proxy Enabled. . . . . : No Ethernet adapter Local Area Connection: Host Name . . . . . . . . . : client1.microsoft.com DNS Servers . . . . . . . . : 10.1.0.200 Description . . . . . . . . : 3Com 3C90x Ethernet Adapter Physical Address. . . . . . : 00-60-08-3E-46-07 DHCP Enabled. . . . . . . . : Yes Autoconfiguration Enabled . : Yes IP Address. . . . . . . . . : 192.168.0.112 Subnet Mask . . . . . . . . : 255.255.0.0 Default Gateway . . . . . . : 192.168.0.1 DHCP Server . . . . . . . . : 10.1.0.50 Primary WINS Server . . . . : 10.1.0.101 Secondary WINS Server . . . : 10.1.0.102 Lease Obtained. . . . . . . : Wednesday, September 02, 1998 10:32:13 AM Lease Expires . . . . . . . : Friday, September 18, 1998 10:32:13 AM
If no problems appear in the TCP/IP configuration, the next step is testing the ability to connect to other host computers on the TCP/IP network.
Viewing configuration by using the Status feature
An alternate method of viewing configuration is available through the Status feature of a network connection. For more information, see View the status of a local area connection.
Refreshing configuration by using ipconfig /renew
When you troubleshoot a TCP/IP networking problem, begin by checking the TCP/IP configuration on the computer that is experiencing the problem. If the computer is DHCP-enabled and is using a DHCP server to obtain configuration, you can initiate a refresh of the lease by using the ipconfig /renew command.
When you use ipconfig /renew, all network adapters on the computer that uses DHCP (except those that are manually configured) try to contact a DHCP server and renew their existing configuration or obtain a new configuration.
You can also use the ipconfig command with the /release option to immediately release the current DHCP configuration for a host.
As an alternative to ipconfig you can use Repair to renew LAN or high-speed Internet connection IP settings. Repair performs a series of commands that repair a connection. The commands that are invoked by Repairare listed below with their command-line equivalents:
For more information, see Repair a LAN or high-speed Internet connection.
Managing DNS and DHCP class IDs by using ipconfig
You can also use the ipconfig command to:
Testing connections by using ping
The ping command helps to verify IP-level connectivity. When troubleshooting, you can use ping to send an ICMP echo request to a target host name or IP address. Use ping whenever you need to verify that a host computer can connect to the TCP/IP network and network resources. You can also use ping to isolate network hardware problems and incompatible configurations.
It is usually best to verify that a route exists between the local computer and a network host by first using the ping command and the IP address of the network host to which you want to connect. Try pinging the IP address of the target host to see if it responds, as follows:
You should perform the following steps when using ping:
The ping command uses Windows Sockets-style name resolution to resolve a computer name to an IP address, so if pinging by address succeeds, but pinging by name fails, then the problem lies in address or name resolution, not network connectivity. For more information, see Troubleshooting hardware addresses by using arp.
If you cannot use ping successfully at any point, confirm that:
You can use different options with the ping command to specify the size of packets to use, how many packets to send, whether to record the route used, what Time-to-Live (TTL) value to use, and whether to set the "don't fragment" flag. You can type ping -? to see these options.
The following example illustrates how to send two pings, each 1,450 bytes in size, to IP address 220.127.116.11:
C:\>ping -n 2 -l 1450 18.104.22.168 Pinging 22.214.171.124 with 1450 bytes of data: Reply from 126.96.36.199: bytes=1450 time<10ms TTL=32 Reply from 188.8.131.52: bytes=1450 time<10ms TTL=32 Ping statistics for 184.108.40.206: Packets: Sent = 2, Received = 2, Lost = 0 (0% loss), Approximate roundtrip times in milliseconds: Minimum = 0ms, Maximum = 10ms, Average = 2ms
By default, ping waits 4,000 milliseconds (4 seconds) for each response to be returned before displaying the "Request Timed Out" message. If the remote system being pinged is across a high-delay link, such as a satellite link, responses may take longer to be returned. You can use the -w (wait) option to specify a longer time-out.
Troubleshooting hardware addresses by using arp
The Address Resolution protocol (ARP) allows a host to find the media access control address of a host on the same physical network, given the IP address of the host. To make ARP efficient, each computer caches IP-to-media access control address mappings to eliminate repetitive ARP broadcast requests.
You can use the arp command to view and modify the ARP table entries on the local computer. The arp command is useful for viewing the ARP cache and resolving address resolution problems.
Troubleshooting NetBIOS names by using nbtstat
NetBIOS over TCP/IP (NetBT) resolves NetBIOS names to IP addresses. TCP/IP provides many options for NetBIOS name resolution, including local cache lookup, WINS server query, broadcast, DNS server query, and Lmhosts and Hosts file lookup.
Nbtstat is a useful tool for troubleshooting NetBIOS name resolution problems. You can use the nbtstat command to remove or correct preloaded entries:
Displaying connection statistics by using netstat
You can use the netstat command to display protocol statistics and current TCP/IP connections. The netstat -a command displays all connections, and netstat -r displays the route table plus active connections. Thenetstat -o command displays process IDs so you can view the owner of the port for each connection. The netstat -e command displays Ethernet statistics, and netstat -s displays per-protocol statistics. If you usenetstat -n, addresses and port numbers are not converted to names. The following shows sample output for netstat:
C:\>netstat -e Interface Statistics Received Sent Bytes 3995837940 47224622 Unicast packets 120099 131015 Non-unicast packets 7579544 3823 Discards 0 0 Errors 0 0 Unknown protocols 363054211 C:\>netstat -n -o Active Connections proto Local Address Foreign Address State PID TCP 172.31.71.152:1136 220.127.116.11:389 CLOSE_WAIT 180 TCP 172.31.71.152:2730 172.31.71.99:139 ESTABLISHED 4 TCP 172.31.71.152:3110 18.104.22.168:389 CLOSE_WAIT 364 TCP 172.31.71.152:3796 172.30.236.233:1479 ESTABLISHED 1128 TCP 172.31.71.152:3800 172.30.236.233:1740 ESTABLISHED 1128 TCP 172.31.71.152:3815 172.30.236.233:1479 ESTABLISHED 908 TCP 172.31.71.152:3819 172.30.236.233:1740 ESTABLISHED 908 TCP 172.31.71.152:4034 172.31.16.197:139 TIME_WAIT 0 TCP 172.31.71.152:4037 22.214.171.124:445 TIME_WAIT 0 TCP 172.31.71.152:4043 126.96.36.199:119 TIME_WAIT 0 TCP 172.31.71.152:4044 188.8.131.52:119 TIME_WAIT 0 TCP 172.31.71.152:4045 184.108.40.206:119 TIME_WAIT 0 TCP 172.31.71.152:4046 220.127.116.11:119 TIME_WAIT 0 TCP 172.31.71.152:4047 18.104.22.168:119 TIME_WAIT 0 TCP 172.31.71.152:4048 22.214.171.124:119 TIME_WAIT 0 TCP 172.31.71.152:4049 126.96.36.199:119 TIME_WAIT 0 TCP 172.31.71.152:4050 188.8.131.52:119 TIME_WAIT 0 C:\>netstat -a Active Connections proto Local Address Foreign Address State TCP CORP1:1572 172.16.48.10:nbsession ESTABLISHED TCP CORP1:1589 172.16.48.10:nbsession ESTABLISHED TCP CORP1:1606 172.16.105.245:nbsession ESTABLISHED TCP CORP1:1632 172.16.48.213:nbsession ESTABLISHED TCP CORP1:1659 172.16.48.169:nbsession ESTABLISHED TCP CORP1:1714 172.16.48.203:nbsession ESTABLISHED TCP CORP1:1719 172.16.48.36:nbsession ESTABLISHED TCP CORP1:1241 172.16.48.101:nbsession ESTABLISHED UDP CORP1:1025 *:* UDP CORP1:snmp *:* UDP CORP1:nbname *:* UDP CORP1:nbdatagram *:* UDP CORP1:nbname *:* UDP CORP1:nbdatagram *:* C:\>netstat -s IP Statistics Packets Received = 5378528 Received Header Errors = 738854 Received Address Errors = 23150 Datagrams Forwarded = 0 Unknown protocols Received = 0 Received Packets Discarded = 0 Received Packets Delivered = 4616524 Output Requests = 132702 Routing Discards = 157 Discarded Output Packets = 0 Output Packet No Route = 0 Reassembly Required = 0 Reassembly Successful = 0 Reassembly Failures = 0 Datagrams Successfully Fragmented = 0 Datagrams Failing Fragmentation = 0 Fragments Created = 0 ICMP Statistics Received Sent Messages 693 4 Errors 0 0 Destination Unreachable 685 0 Time Exceeded 0 0 Parameter problems 0 0 Source Quenches 0 0 Redirects 0 0 Echoes 4 0 Echo Replies 0 4 Timestamps 0 0 Timestamp Replies 0 0 Address Masks 0 0 Address Mask Replies 0 0 TCP Statistics Active Opens = 597 Passive Opens = 135 Failed Connection Attempts = 107 Reset Connections = 91 Current Connections = 8 Segments Received = 106770 Segments Sent = 118431 Segments Retransmitted = 461 UDP Statistics Datagrams Received = 4157136 No Ports = 351928 Receive Errors = 2 Datagrams Sent = 13809
Tracing network connections by using tracert
Tracert (Trace Route) is a route-tracing utility that is used to determine the path that an IP datagram takes to reach a destination. The tracert command uses the IP Time-to-Live (TTL) field and ICMP error messages to determine the route from one host to another through a network.
How tracert works
The Tracert diagnostic utility determines the route taken to a destination by sending Internet Control Message protocol (ICMP) echo packets with varying IP Time-to-Live (TTL) values to the destination. Each router along the path is required to decrement the TTL on a packet by at least 1 before forwarding it. When the TTL on a packet reaches 0, the router should send an "ICMP Time Exceeded" message back to the source computer.
Tracert determines the route by sending the first echo packet with a TTL of 1 and incrementing the TTL by 1 on each subsequent transmission until the target responds or the maximum TTL is reached. The route is determined by examining the "ICMP Time Exceeded" messages sent back by intermediate routers. Some routers silently drop packets with expired TTLs and are invisible to the Tracert utility.
The tracert command prints out an ordered list of the near-side interface of the routers in the path that returned the "ICMP Time Exceeded" message. If the -d option is used, the Tracert utility does not perform a DNS lookup on each IP address.
In the following example, the packet must travel through two routers (10.0.0.1 and 192.168.0.1) to get to host 172.16.0.99. The default gateway of the host is 10.0.0.1 and the IP address of the router on the 192.168.0.0 network is 192.168.0.1.
C:\>tracert 172.16.0.99 -d Tracing route to 172.16.0.99 over a maximum of 30 hops 1 2 ms 3 ms 2 ms 10.0.0.1 2 75 ms 83 ms 88 ms 192.168.0.1 3 73 ms 79 ms 93 ms 172.16.0.99 Trace complete.
Troubleshooting with tracert
You can use the tracert command to determine where a packet stopped on the network. In the following example, the default gateway has determined that there is not a valid path for the host on 192.168.10.99. There is probably a router configuration problem or the 192.168.10.0 network does not exist (a bad IP address).
C:\>tracert 192.168.10.99 Tracing route to 192.168.10.99 over a maximum of 30 hops 1 10.0.0.1 reports: Destination net unreachable. Trace complete.
The Tracert utility is useful for troubleshooting large networks where several paths can be taken to arrive at the same point.
Tracert command-line options
The tracert command supports several options, as shown in the following table.
tracert [-d] [-h maximum_hops] [-j host-list] [-w timeout] target_name
For more information, see Trace a path by using the tracert command.
Testing routers by using pathping
The pathping command is a route tracing tool that combines features of the ping and tracert commands with additional information that neither of those tools provides. The pathping command sends packets to each router on the way to a final destination over a period of time, and then computes results based on the packets returned from each hop. Since the command shows the degree of packet loss at any given router or link, it is easy to determine which routers or links might be causing network problems. A number of options are available, as shown in the following table.
The default number of hops is 30, and the default wait time before a time-out is 3 seconds. The default period is 250 milliseconds, and the default number of queries to each router along the path is 100.
The following is a typical pathping report. The compiled statistics that follow the hop list indicate packet loss at each individual router.
D:\>pathping -n server1 Tracing route to server1 [10.54.1.196] over a maximum of 30 hops: 0 172.16.87.35 1 172.16.87.218 2 192.168.52.1 3 192.168.80.1 4 10.54.247.14 5 10.54.1.196 Computing statistics for 125 seconds... Source to Here This Node/Link Hop RTT Lost/Sent = Pct Lost/Sent = Pct Address 0 172.16.87.35 0/ 100 = 0% | 1 41ms 0/ 100 = 0% 0/ 100 = 0% 172.16.87.218 13/ 100 = 13% | 2 22ms 16/ 100 = 16% 3/ 100 = 3% 192.168.52.1 0/ 100 = 0% | 3 24ms 13/ 100 = 13% 0/ 100 = 0% 192.168.80.1 0/ 100 = 0% | 4 21ms 14/ 100 = 14% 1/ 100 = 1% 10.54.247.14 0/ 100 = 0% | 5 24ms 13/ 100 = 13% 0/ 100 = 0% 10.54.1.196 Trace complete.
When pathping is run, you first see the results for the route as it is tested for problems. This is the same path that is shown by the tracert command. The pathping command then displays a busy message for the next 125 seconds (this time varies by the hop count). During this time, pathping gathers information from all the routers previously listed and from the links between them. At the end of this period, it displays the test results.
The two rightmost columns--This Node/Link Lost/Sent=Pct and Address--contain the most useful information. The link between 172.16.87.218 (hop 1), and 192.168.52.1 (hop 2) is dropping 13 percent of the packets. All other links are working normally. The routers at hops 2 and 4 also drop packets addressed to them (as shown in the This Node/Link column), but this loss does not affect their forwarding path.
The loss rates displayed for the links (marked as a | in the rightmost column) indicate losses of packets being forwarded along the path. This loss indicates link congestion. The loss rates displayed for routers (indicated by their IP addresses in the rightmost column) indicate that those routers' CPUs might be overloaded. These congested routers might also be a factor in end-to-end problems, especially if packets are forwarded by software routers.