Using TRACERT to Troubleshoot TCP/IP Problems in Windows NT

• Microsoft Windows NT Server versions 3.5, 3.51, 4.0
• Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0

SUMMARY

The TRACERT (Trace Route) command is a route-tracing utility used to determine the path that an IP packet has taken to reach a destination.

This article discusses the following topics:

• How the TRACERT command works
• Troubleshooting with TRACERT
• TRACERT syntax

MORE INFORMATION

How the TRACERT Command 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, so the TTL is effectively a hop count. 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. Note that some routers silently drop packets with expired TTLs and are invisible to TRACERT.

TRACERT prints out an ordered list of the routers in the path that returned the ICMP Time Exceeded message. If the -d switch is used (telling TRACERT not to perform a DNS lookup on each IP address), the IP address of the near- side interface of the routers is reported.

In the following example, the packet must travel through two routers (157.54.48.1 and 11.1.0.67) to get to host 11.1.0.1. In this example, the default gateway is 157.54.48.1 and the IP address of the router on the 11.1.0.0 network is at 11.1.0.67.

   C:\>tracert 11.1.0.1

   Tracing route to 11.1.0.1 over a maximum of 30 hops

   1     2 ms     3 ms     2 ms  157.54.48.1
   2    75 ms    83 ms    88 ms  11.1.0.67
   3    73 ms    79 ms    93 ms  11.1.0.1

   Trace complete.

Troubleshooting with TRACERT

The TRACERT command can be used 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 22.110.0.1. There is probably a router configuration problem or the 22.110.0.0 network does not exist (a bad IP address).

   C:\>tracert 22.110.0.1

   Tracing route to 22.110.0.1 over a maximum of 30 hops

   1  157.54.48.1  reports: Destination net unreachable.

   Trace complete.

TRACERT syntax

There are several command-line switches that can be used with TRACERT, but they are usually not needed for standard troubleshooting.

TRACERT syntax:

   tracert [-d] [-h maximum_hops] [-j host-list] [-w timeout] target_name

   -d
      Specifies to not resolve addresses to host names.

   -h maximum_hops
      Specifies the maximum number of hops to search for target.

   -j host-list
      Specifies loose source route along the host-list.

   -w timeout
      Waits the number of milliseconds specified by timeout for each
      reply.

   target_name
      Name or IP address of the target host.