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DiagnosticsPrivileged EXEC

traceroute [ip] source [intf]

Traces the route packets take to a destination IP address, using a specified source interface for the outgoing probes, to test path connectivity and identify routing issues.

Syntax·Privileged EXEC
traceroute [ip] source [intf]

When to Use This Command

  • Verify the path from a specific interface (e.g., loopback) to a remote server when multiple paths exist.
  • Troubleshoot asymmetric routing by forcing probes out a particular interface.
  • Test connectivity from a management interface to a core network device.
  • Validate that traffic from a specific subnet (via its interface) reaches a destination correctly.

Command Examples

Traceroute from Loopback0 to 8.8.8.8

traceroute 8.8.8.8 source Loopback0
Type 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 4 msec 4 msec 4 msec
  2 10.0.0.1 8 msec 8 msec 8 msec
  3 172.16.0.1 12 msec 12 msec 12 msec
  4 8.8.8.8 16 msec 16 msec 16 msec

Line 1: First hop is 192.168.1.1 with 4 ms round-trip time for each probe. Line 2: Second hop 10.0.0.1 with 8 ms. Line 3: Third hop 172.16.0.1 with 12 ms. Line 4: Destination 8.8.8.8 reached in 16 ms. Each line shows hop number, IP address, and three probe times. Increasing times indicate normal latency accumulation; sudden jumps may indicate congestion or suboptimal paths.

Traceroute with source interface GigabitEthernet0/1 to 10.10.10.1

traceroute 10.10.10.1 source GigabitEthernet0/1
Type escape sequence to abort.
Tracing the route to 10.10.10.1
VRF info: (vrf in name/id, vrf out name/id)
  1 10.0.0.2 2 msec 2 msec 2 msec
  2 10.0.0.5 6 msec 6 msec 6 msec
  3 * * *
  4 10.10.10.1 20 msec 20 msec 20 msec

First hop 10.0.0.2 (2 ms), second hop 10.0.0.5 (6 ms). Third hop shows asterisks (* * *) meaning no response within timeout (possible firewall or routing issue). Fourth hop reaches destination 10.10.10.1 (20 ms). Asterisks indicate packet loss or filtering at that hop; if destination is reached, the path is still functional but that hop may be hidden.

Understanding the Output

The output lists each hop (router) along the path to the destination. Each line shows the hop number, the IP address of the responding router, and three round-trip times (in milliseconds) for three probes. Times are typically low (1-10 ms) on LANs and increase with distance. Values over 100 ms may indicate high latency or congestion. Asterisks (*) mean the probe timed out (no response), which could be due to ICMP filtering, packet loss, or a routing loop. If the destination is reached, asterisks at intermediate hops are often due to security policies. The source interface ensures probes originate from that interface's IP address, which is useful for testing specific paths or when multiple IPs exist on the router.

CCNA Exam Tips

1.

CCNA exam tip: The 'source' option forces the traceroute to use the IP of the specified interface as the source address; this is tested in troubleshooting scenarios.

2.

CCNA exam tip: Asterisks in output do not always mean failure; if the destination is reached, they may indicate a device that does not respond to ICMP time-exceeded messages.

3.

CCNA exam tip: Traceroute uses UDP probes by default on Cisco IOS (destination port 33434+); the 'source' option does not change the protocol.

4.

CCNA exam tip: You can abort a traceroute with Ctrl+Shift+6, then X.

Common Mistakes

Mistake 1: Forgetting to specify the source interface when multiple paths exist, leading to misleading results (e.g., using management interface instead of the intended data interface).

Mistake 2: Confusing 'source' with 'destination' — the source interface must be a valid interface on the local router.

Mistake 3: Assuming asterisks always indicate a broken path; they may simply be due to ICMP filtering at that hop.

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 route

Displays the current IP routing table on a Cisco router, used to verify routes, check next-hop addresses, and troubleshoot connectivity issues.

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.

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