What it does
tracepath traces the route packets take to a destination,
similar to traceroute, but also discovers the path MTU (PMTU)
along the way. It works without requiring raw socket privileges.
How it works (mechanical)
tracepath sends UDP probes with increasing TTL (hop limit).
Routers respond with ICMP “time exceeded” messages. When a router reports
“fragmentation needed,” tracepath learns the MTU for that hop.
- Uses UDP probes (not ICMP echo)
- Relies on ICMP error responses
- Automatically discovers path MTU
- No raw socket access required
10 Practical Examples
# 1) Trace path to a host tracepath example.com
# 2) Trace to an IP address tracepath 8.8.8.8
# 3) IPv6 trace tracepath6 ipv6.google.com
# 4) Show numeric output only tracepath -n example.com
# 5) Limit maximum hops tracepath -m 20 example.com
# 6) Diagnose PMTU black holes tracepath large-file.example.com
# 7) Compare with traceroute output tracepath example.com traceroute example.com
# 8) Trace a local gateway path
tracepath $(ip route show default | awk '{print $3}')# 9) Script-friendly single-run tracepath -n example.com | tail -n 1
# 10) Debug VPN MTU issues tracepath vpn-endpoint.example.com
Notes & Gotchas
- Some routers block or rate-limit ICMP responses.
- Final hops may show “no reply” even when connectivity works.
- MTU discovery is the key advantage over
traceroute. - Results differ from ICMP-based traceroute.
- Use for MTU issues, not latency benchmarking.
Historical Context
tracepath was introduced as part of iputils to provide
a safer traceroute-like tool that works without raw sockets and adds
automatic PMTU discovery.
Modern Equivalent / Related Tools
- traceroute — classic hop-by-hop tracing
- mtr — combined traceroute and ping
- ping — reachability and latency
- ip route — routing decisions
- tcpdump — packet-level verification