I am trying to find out what happens when you try to access a site using traceroute command, but I cannot find any site that is actually blocking me. Anyway, I wanted to ask what happens when a firewall blocks traceroute? And if I am correct, the firewall blocks all ports that traceroute would use right? What happens to that traceroute exactly?
There is no "blocking" of traceroute, tracepath, tracert or whatever the tool gets called. These commands work by setting the TTL/hoplimit of the packet to a specific value and then expect the host to send an ICMP unreachable back if the TTL/hoplimit expired (i.e. decremented to zero). If a system does not send this ICMP message or if a middlebox (like a firewall) blocks the delivery of the ICMP packet then the host with the specific TTL/hoplimit will show up as unknown in traceroute.