What is traceroute and how does it help in troubleshooting?

Traceroute returns the list of hops (routers) a packet crosses to the destination, so unlike ping it shows where along the path a Layer 3 problem occurs.

Verify Connectivity with Traceroute:

While ping determines if there is Layer 3 connectivity, it does not identify where the problem is located along the path.

Traceroute:

• Can help locate Layer 3 problem areas in a network
• Returns a list of hops as a packet is routed through a network
• Shows each router (hop) along the path to the destination

Command Syntax:

Output Interpretation:

C:\> tracert 10.1.1.10
  1    2 ms    2 ms    2 ms   192.168.10.1
  2    *       *       *      Request timed out.
  3    *       *       *      Request timed out.

• Successful hop shows IP address and round-trip times
• Asterisk (*) indicates the hop timed out or didn't respond
• In the example above, there appears to be a problem between R1 and R2

Interrupt commands:

• Windows: Ctrl-C
• Cisco IOS: Ctrl-Shift-6

Go deeper:

• Wikipedia — Traceroute — how incrementing TTL maps each hop, and how to read the round-trip times and timeouts.