traceroute [ip]
Traces the route packets take from the source device to a destination IP address, showing each hop along the path, used to diagnose network path issues and latency.
traceroute [ip]When to Use This Command
- Verify the path to a remote server when users report connectivity problems.
- Identify where packet loss or high latency occurs in a multi-hop network.
- Troubleshoot routing loops or asymmetric routing by comparing forward and reverse paths.
- Confirm that traffic is traversing expected next-hop routers in a complex topology.
Command Examples
Basic traceroute to a remote host
traceroute 8.8.8.8Type escape sequence to abort. Tracing the route to 8.8.8.8 VRF info: (vrf in name/id, vrf out name/id) 1 192.168.1.1 1 msec 1 msec 1 msec 2 10.0.0.1 5 msec 4 msec 4 msec 3 172.16.1.1 10 msec 10 msec 9 msec 4 8.8.8.8 12 msec 11 msec 12 msec
Each line shows a hop number, the IP address of the router that responded, and the round-trip time (RTT) for three probes in milliseconds. The first hop is the default gateway, subsequent hops are intermediate routers, and the final hop is the destination.
Traceroute with extended options to specify source interface
traceroute 10.10.10.1 source loopback 0Type escape sequence to abort. Tracing the route to 10.10.10.1 VRF info: (vrf in name/id, vrf out name/id) 1 192.168.2.1 2 msec 2 msec 1 msec 2 10.10.10.1 3 msec * 3 msec
The source is set to Loopback0 IP. The asterisk (*) indicates a probe that timed out, which could be due to ICMP rate-limiting or packet loss. The output still shows the path with one hop and the destination.
Understanding the Output
The output begins with a header line indicating the destination. Each subsequent line represents a hop (router) along the path. The hop number is followed by the IP address of the responding router. Three probe times are shown in milliseconds; if a probe times out, an asterisk (*) appears. Consistent high latency or timeouts at a specific hop indicate a problem. The final hop should be the destination IP; if it is not reached, the last responding hop is where the failure occurs.
CCNA Exam Tips
Remember that traceroute uses UDP packets with increasing TTL values by default on Cisco IOS; ICMP echo requests are used on Windows.
An asterisk (*) in output may indicate a router that does not respond to traceroute probes (e.g., due to ACLs or rate-limiting), not necessarily a failure.
The command 'traceroute' is used in Privileged EXEC mode; in user EXEC mode, use 'traceroute' also works but may have limited options.
Know that the 'source' option allows you to specify a different source IP, useful for testing from specific interfaces.
Common Mistakes
Mistake: Forgetting that traceroute uses UDP and may be blocked by firewalls; use extended options to change to ICMP if needed.
Mistake: Interpreting a single asterisk as a failure; multiple consecutive asterisks indicate a true problem.
Mistake: Not using the 'source' option when troubleshooting from a specific subnet, leading to misleading paths.
Related Commands
ping [ip]
The ping command sends ICMP echo requests to a destination IP address to test network connectivity and measure round-trip time.
show ip interface brief
Displays a summary of all IP interfaces on the device, including their IP address, status, and protocol state, used for quick verification of interface configuration and connectivity.
show ip route
Displays the current IP routing table on a Cisco router, used to verify routes, check next-hop addresses, and troubleshoot connectivity issues.
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