Firewalk, covered in CEH v13 Module 03, is a firewall analysis tool that uses TTL-limited probes to determine which ports are allowed through a filtering device (firewall/router).

If a Time-to-Live Exceeded message is received, it means the packet made it past the firewall and was stopped before reaching the target host.

No response typically means filtered or blocked.

Therefore:

Ports 21 and 22 are filtered by the firewall.

Port 23 triggered a TTL Exceeded, meaning it passed through the firewall, and likely hit a router or was dropped due to TTL=0 before reaching the host.