Web & Networking › Networking Fundamentals

ping and traceroute

Checking reachability and the path packets take.

Also known as: ping, traceroute, tracert, mtr

Two basic tools for diagnosing network problems.

ping: is it reachable, and how fast?

ping sends small test packets (ICMP echo requests) to a host and times the replies.

ping example.com
# 64 bytes from 93.184.216.34: icmp_seq=1 ttl=56 time=12.3 ms
# 64 bytes from 93.184.216.34: icmp_seq=2 ttl=56 time=11.9 ms
# --- 4 packets transmitted, 4 received, 0% packet loss

It tells you:

• Is the host reachable? Replies mean yes.
• Round-trip time (latency) in milliseconds (round-trip time).
• Packet loss, a sign of a poor connection.

Use ping 8.8.8.8 to test internet connectivity without DNS, and ping example.com to test name resolution as well. If the IP works but the name doesn’t, the problem is DNS.

traceroute: what path do packets take?

traceroute example.com        # (tracert on Windows)
#  1  192.168.1.1     1.2 ms
#  2  10.20.0.1       8.5 ms
#  3  * * *
#  4  93.184.216.34  12.0 ms

It lists each router (“hop”) between you and the destination, with the time taken to reach each. It reveals where delay or failure begins. mtr combines ping and traceroute in a live view.

Reading the results carefully

• No reply doesn’t always mean down. Many hosts and firewalls block ICMP, so ping fails while the website works (firewalls).
• * * * lines in traceroute are routers that don’t answer, not necessarily problems. Look at whether later hops respond.
• A single slow hop that isn’t followed by slower ones usually just means that router deprioritizes replies.
• Ping measures the network, not your application. A server can answer ping while the app is broken.

When to use which tool