Extract from Microsoft Support How to Use TRACERT to Troubleshoot TCP/IP Problems in Windows
The TRACERT diagnostic utility determines the route to a destination
by sending Internet Control Message Protocol (ICMP) echo packets to
the destination. In these packets, TRACERT uses varying IP
Time-To-Live (TTL) values. Because each router along the path is
required to decrement the packet's TTL by at least 1 before forwarding
the packet, the TTL is effectively a hop counter. When the TTL on a
packet reaches zero (0), the router sends an ICMP "Time Exceeded"
message back to the source computer.
TRACERT sends the first echo packet with a TTL of 1 and increments the
TTL by 1 on each subsequent transmission, until the destination
responds or until the maximum TTL is reached. The ICMP "Time Exceeded"
messages that intermediate routers send back show the route. Note
however that some routers silently drop packets that have expired
TTLs, and these packets are invisible to TRACERT.
So you can see that tracert rely on the router sending back an ICMP message "Time Exceeded".
Many routers on the Internet
- either are configured to not send ICMP message, those routers won't answer to ping
- either silently drop a TTL expired packet (but may respond to ping)
In both case, tracert doesn't receive any answer and display "Request time out".