I would bet that FiOS has their network set up to basically proxy-reply to any ICMP packet with a TTL of 1 that they receive from customer premises equipment, substituting in the destination of that ICMP message as the source address of the TTL expired they send back, as a way of cutting down on ICMP flooding attacks (DDoS or similar). That's a regular UDP traceroute from my router at top, and then an ICMP traceroute on bottom. In a Linux shell, you can use the parameter -I to run a Windows-style ICMP traceroute instead of the default UDP, and those two behave quite differently. I have FiOS as well, and I suspect they may have their infrastructure set up to handle ICMP traffic a bit differently. MacOS and *nix send out a UDP packet with destination port 33434 (I think they increment the destination port number on each subsequent hop, but I could be wrong).
Windows sends out an ICMP type 8 request (an echo request, same as ping). Where Windows and *nix platforms differ is the type of message they're sending out. Traceroute basically works by first sending out a packet with a TTL of 1, and then recording the source IP of the TTL exceeded message it got back it then sends out a new packet with a TTL of 2 and records the source IP of the TTL exceeded message, then a new packet with a TTL of 3, and so on, until it either gets a TTL exceeded message from the IP address it was trying to reach, or hits a maximum number of hops (usually 30 is the default, as in your tracert). If a router decrements TTL to 0, it will not forward the packet instead it will send a TTL exceeded message back to the IP that originated it. Both commands are relying on a similar mechanism-there's a field in an IP packet called time-to-live (TTL) that starts off at a particular value, and gets decremented by one by each router (hop) it passes through. The traceroute command on MacOS and Linux/Unix platforms works a little differently than the Windows tracert command.
u/RoweDent created this awesome resource on network theory u/tht1kidd_ has created a suggestion post regarding information everyone needs to provide when asking a question about their network There have been some excellent guides written in this sub, and we're always looking for more!
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