How to Use the TRACERT Utility
The TRACERT diagnostic utility determines the route to a destinationby sending Internet Control Message Protocol (ICMP) echo packets to the destination. In these packets, TRACERT uses varying IP Time-To-Live (TTL) values. Because each router along the path is required to decrement the packet's TTL by at least 1 before forwarding the packet, the TTL is effectively a hop counter. When the TTL on a packet reaches zero (0), the router sends an ICMP "Time Exceeded" message back to the source computer.
TRACERT sends the first echo packet with a TTL of 1 and increments the TTL by 1 on each subsequent transmission, until the destination responds or until the maximum TTL is reached. The ICMP "Time Exceeded" messages that intermediate routers send back show the route. Note however that some routers silently drop packets that have expired TTLs, and these packets are invisible to TRACERT.
TRACERT prints out an ordered list of the intermediate routers thatreturn ICMP "Time Exceeded" messages. Using the -d
option with the tracert
command instructs TRACERT not to perform a DNS lookup on each IP address, so that TRACERT reports the IP address of the near-side interface of the routers.
In the following example of the tracert
command and its output, the packet travels through two routers (184.108.40.206 and 220.127.116.11) to get to host 18.104.22.168. In this example, the default gateway is 22.214.171.124 and the IP address of the router on the 126.96.36.199 network is at 188.8.131.52.
The output from the command:
Tracing route to 184.108.40.206 over a maximum of 30 hops --------------------------------------------------- 1 2 ms 3 ms 2 ms 220.127.116.11 2 75 ms 83 ms 88 ms 18.104.22.168 3 73 ms 79 ms 93 ms 22.214.171.124 Trace complete.
How to Use TRACERT to Troubleshoot
You can use TRACERT to find out where a packet stopped on the network. In the following example, the default gateway has found that there is no valid path for the host on 126.96.36.199. Probably, either the router has a configuration problem, or the 188.8.131.52 network does not exist, reflecting a bad IP address.
The output from the command:
Tracing route to 184.108.40.206 over a maximum of 30 hops ----------------------------------------------------- 1 220.127.116.11 reports: Destination net unreachable. Trace complete.
TRACERT is useful for troubleshooting large networks where several pathscan lead to the same point or where many intermediate components (routers or bridges) are involved.
How to Use TRACERT Options
There are several command-line options that you can use with TRACERT, although the options are not usually necessary for standard troubleshooting.
The following example of command syntax shows all of the possible options:
tracert -d -h maximum_hops -j host-list -w timeout target_host
What the parameters do:
-d Specifies to not resolve addresses to host names -h maximum_hops Specifies the maximum number of hops to search for the 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_host Specifies the name or IP address of the target host