traceroute in Linux

1. What Is traceroute?

traceroute is used to discover the route that packets take to reach a remote host. It helps network engineers understand delays and determine whether intermediate hops are reachable. It works by sending UDP or ICMP packets with increasing TTL (Time To Live) values.

2. Installing traceroute

It may require installation depending on your distribution:

sudo apt install traceroute      # Debian / Ubuntu

sudo yum install traceroute      # RHEL / CentOS

sudo pacman -S traceroute        # Arch Linux

3. Basic Usage

traceroute destination

Example:

traceroute google.com

4. Common Options

Option	Description	Example
-n	Don't resolve hostnames	`traceroute -n google.com`
-m	Set max TTL (hops)	`traceroute -m 20 google.com`
-w	Wait time for reply (seconds)	`traceroute -w 3 google.com`
-p	Set UDP port	`traceroute -p 33434 google.com`
-I	Use ICMP instead of UDP	`traceroute -I google.com`

5. Output Explanation


traceroute to google.com (142.250.72.14), 30 hops max
 1  192.168.1.1 (192.168.1.1)  1.123 ms  1.217 ms  1.201 ms
 2  10.0.0.1 (10.0.0.1)        3.438 ms  3.302 ms  3.446 ms
 3  * * *

Each line represents one hop
Three timing samples indicate latency in ms
* indicates no response from that hop (timeout)

6. Practical Examples

Trace to a local device:
```
traceroute 192.168.0.100
```
Analyze ISP routing:
```
traceroute google.com
```
Use ICMP for firewall bypass:
```
traceroute -I example.com
```

7. Comparison with ping

Feature	ping	traceroute
Connectivity check	✅	✅
Path discovery	❌	✅
Hop count visibility	❌	✅
Protocol	ICMP	UDP or ICMP

8. Limitations and Considerations

Routers may block or filter ICMP or UDP packets
Asterisks indicate non-responsive nodes—could be firewall or routing policy
Traceroute output may be incomplete in private or protected networks

9. Conclusion

traceroute is an essential tool for analyzing network paths. It helps locate bottlenecks, understand latency, and monitor routing behavior across internal and external networks. Mastering its syntax and output interpretation makes it invaluable for network diagnostics.