Traceroute is a utility that traces a packet from your computer to an Internet host, but it will show you how many hops the packet requires to reach the host and how long each hop takes. If you're visiting a Web site and pages are appearing slowly, you can use traceroute to figure out where the longest delays are occurring. Traceroute utilities work by sending packets with low time-to-live (TTL) fields. The TTL value specifies how many hops the packet is allowed before it is returned. When a packet can't reach its destination because the TTL value is too low, the last host returns the packet and identifies itself. By sending a series of packets and incrementing the TTL value with each successive packet, traceroute finds out who all the intermediary hosts are.The original traceroute is a UNIX utility, but nearly all platforms have something similar. Windows includes a traceroute utility called tracert. On a Windows PC you can run traceroute using a command prompt To do this, go to the Windows Start button, choose Programs, then MSDOS Prompt. When you get the C: prompt, type tracert followed by the destination server name or an IP address, for example: tracert google.com
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.
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
Parameters:
-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.
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