Re: I never thought of this scenario

On 4/22/24 05:35, The Natural Philosopher wrote:

Routing itself *is* network address translation.

Nope.

The router removes the current next hop address and replaces it with a new one, and it reduces the TTL field.

Nope.
Run a sniffer on your Internet traffic and you will see that traffic is being sent to the destination IP address of the remote server, not your local router.
In the spirit of the benefit of doubt / nomenclature type problem, I believe that you may be conflating what happens with MAC addresses and what happens with IP addresses on Ethernet (or probably any 802 network).
Routing between Ethernet networks wholesale replaces the source and destination MAC address of the Ethernet frame.  But without NAT, the source and destination IP address do not change.

All NAT does is replace the *source* destination/port as well, and store the originating port/ip address ready for return packets.

Source NAT replaces the source IP and possibly, but no guarantee, the source port.
Destination NAT replaces the destination IP and possibly, but no guarantee, the destination port.
Most, but not all, SOHO routers do source NAT to replace the private unrouted LAN IP with the public Internet IP of the SOHO router.  But that is a very special configuration.
All the routers at the ISP, the core of the Internet, and the server's hosting provider don't modify either the source nor destination IP address.

Where that happens in time  is purely implementation dependent. It might even happen simultaneously with a multicore CPU

There is a logical sequence of events.  You have to choose where the IP packet is going to go before you can do anything else to it as that decision may influence what is done to it.

As an engineer all  that a router does is modify some or all of the information in a packet header, look up where the next hop is in its routing tables, and receive dynamic updates to those routing tables where appropriate. And forward the *modified* packet to the next hop.

The IP packet isn't modified save for a TTL decremnt
The outgoing Ethernet frame is brand new and using different information than the incoming Ethernet frame.
--
Grant. . . .