Cheatsheet & Examples: traceroute

Cheatsheet & Examples: traceroute

Traceroute is a network diagnostic tool used to trace the path packets take from a source to a destination IP address or hostname. It displays the sequence of routers (hops) traversed, along with the round-trip time (RTT) for each hop. This information helps in identifying network bottlenecks or problems.

Basic Traceroute to a Host

Example Usage: traceroute google.com

What it does: This will trace the route to google.com, displaying each hop's IP address and RTT. It uses UDP packets by default.

Command-line Arguments Explained:

hostname: The hostname or IP address to which you want to trace the route.

Specifying the Number of Hops

Example Usage: traceroute -m 20 google.com

What it does: This traces the route to google.com but limits the maximum number of hops to 20. This can be useful if you suspect a routing loop or to speed up the trace.

Command-line Arguments Explained:

-m: Specifies the maximum TTL (Time To Live) value, which determines the maximum number of hops.
20: Sets the maximum TTL to 20.
hostname: The hostname or IP address to which you want to trace the route.

Specifying the Probe Size

Example Usage: traceroute -s 64 google.com

What it does: This sets the probe size to 64 bytes. This might be necessary to work around firewalls or other network devices that filter based on packet size.

Command-line Arguments Explained:

-s: Specifies the packet size (in bytes) to use for the probes.
64: Sets the packet size to 64 bytes.
hostname: The hostname or IP address to which you want to trace the route.

Using ICMP instead of UDP

Example Usage: traceroute -I google.com

What it does: This forces traceroute to use ICMP echo requests (like ping) instead of the default UDP packets. This can be useful if UDP traffic is blocked.

Command-line Arguments Explained:

-I: Uses ICMP echo requests.
hostname: The hostname or IP address to which you want to trace the route.

Setting the Port Number

Example Usage: traceroute -p 80 google.com

What it does: This specifies the destination port number for UDP probes. By default, traceroute uses a range of ports. Specifying a port number might be helpful in troubleshooting issues related to a specific application that uses that port.

Command-line Arguments Explained:

-p: Specifies the destination port number.
80: Sets the destination port to 80 (HTTP).
hostname: The hostname or IP address to which you want to trace the route.

Setting the Source Address

Example Usage: traceroute -S 192.168.1.100 google.com

What it does: This sets the source IP address for the traceroute probes. This can be helpful if you have multiple network interfaces or if you need to simulate traffic from a specific IP address. Note that you may need appropriate permissions and the IP address must be configured on your machine.

Command-line Arguments Explained:

-S: Specifies the source IP address.
192.168.1.100: Sets the source IP address to 192.168.1.100.
hostname: The hostname or IP address to which you want to trace the route.