Like this article? We recommend
Like this article? We recommend
Like this article? We recommend
traceroute
The traceroute tool provides a UDP-based system for tracing the flow of traffic through a network. traceroute uses the TTL field of the IP header to force each hop along the path to return an ICMP Time Exceeded message. The destination host is recognized because it returns an ICMP Destination Unreachable message.
The first set of packets is sent with a TTL of 1, which times out at the first router. The second set of packets has a TTL of 2 and times out at the second router. This pattern is followed until the destination host is reached.
traceroute at Work
As each packet is sent, the results are displayed.The results of a traceroute session are shown in Listing 5.
Listing 5 traceroute Results
[pate@router pate]$ traceroute
bigfun.whirlycott.com
Password:
traceroute to bigfun.whirlycott.com (206.66.240.72), 30 hops max,
38 byte packets
1 mmgw32.bos1.Level3.net (63.212.201.240) 113.711 ms 118.560 ms
109.549 ms
2 mmcu32.bos1.Level3.net (209.244.39.26) 109.146 ms 109.135 ms
109.534 ms
3 gis-gate.gis.net (209.113.128.1) 109.215 ms 109.112 ms 109.429 ms
4 serial2-0-1.hsa1.bos1.Level3.net (166.90.184.1) 109.280 ms
109.070 ms .109.377 ms
5 lo0.mp2.NewYork1.level3.net (209.247.8.252) 119.213 ms 118.905 ms
109.563 .ms
6 209.247.10.46 (209.247.10.46) 119.125 ms 118.996 ms 119.365 ms
7 ATM1-0.BR2.NYC9.ALTER.NET (137.39.52.9) 119.551 ms 119.005 ms
119.413 ms
8 518.at-5-0-0.XR2.NYC9.ALTER.NET (152.63.22.230) 119.254 ms
108.976 ms .119.354 ms
9 180.ATM6-0.XR2.BOS1.ALTER.NET (152.63.16.217) 119.323 ms 119.070 ms
119.328 .ms
10 190.ATM9-0-0.GW1.BOS1.ALTER.NET (146.188.176.237) 129.204 ms
118.981 ms .119.454 ms
11 mdc-gw.customer.ALTER.NET (157.130.1.178) 149.267 ms 129.104 ms
129.498 ms
12 bigfun.whirlycott.com (206.66.240.72) 139.251 ms 129.062 ms
139.349 ms
[pate@router pate]$
The first line of output gives a summary of the data to be sent.The following lines show which hop of the path, the hostname and/or IP address of the router for that hop, and the round-trip time for that packet. In this example everything looks pretty good—there are no big jumps in the round-trip time, no packets were dropped, and even the final round-trip time looks pretty small.
The results in Listing 6 aren't quite so healthy, although they still aren't too bad. There are several spikes in the round-trip time and even a dropped packet at the destination host (the * marker).
Listing 6 A Less Healthy Route
[root@cherry /root]# traceroute http://www.vii.com traceroute to lonepeak.vii.com (206.71.77.2), 30 hops max,
Just as many packet filters are configured to block ping, many are configured to stop traceroute from working as well. Although this limits the usefulness of traceroute for end-to-end troubleshooting, traceroute can still provide useful information about the path followed between the endpoints of the connections.