Transit gateway does not show up in Traceroute

Question

Does anyone know the reason behind the transit gateway not responding to a traceroute packet. I am able to see the end host respond to a traceroute which goes through a TGW, but the TGW hop shows up as a dot and not ! with an ip address.

What was the logic behind the behavior by AWS?

Answer

There are many places on the internet (and private networks) where routers do not respond during a traceroute. During a traceroute, packets are sent with an ever-increasing TTL (time-to-live) until they reach the destination. At each router hop the TTL is decremented and if it is zero an ICMP Time Exceeded packet is generated and sent back to the origin of the packet (where the traceroute is being run from).

There are many routers on the internet that do not generate these ICMP packets - because it takes time and CPU power - which is better spent routing packets.

That the traceroute succeeds is good. That you don't get every hop along the way is fairly normal in large networks.

Transit gateway does not show up in Traceroute

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