Re: I never thought of this scenario

On 4/21/24 05:17, The Natural Philosopher wrote:

Not at all true in the case of address translation, routing protocols, traffic shaping and the like.

Network address translation isn't routing.  NAT happens /after/ routing happens.
Routing protocols aren't routing.  They exchange route information to program routing tables.  Routing uses said information to do the routing.  Routing protocols aren't required for routing.  Manually entered static routes work perfectly fine.
Traffic shaping isn't routing.  It's altering how fast traffic is sent out.
Routing is deciding which interface to send the packet out and doing so.   Other things may be done before and / or after routing.  But routing is it's own independent thing.

DHCP is similar in that the on;y thing a router has to do is determine its a UDP broadcast, and if it is, work out where to send it, and what return address to give it if any..

Nope.

One would expect the router to simply spoof a MAC address on its interface, and relay responses to that MAC address back to the client network.

Nope.

In short its acting like an ethernet switch or bridge

That's proxy ARP, which is a form of routing in it's own way.

I am more curious as to how the DHCP server 'knows' which network address to give the client, but not interested enough to look it up. :-)

See my most recent reply for a description of how DHCP relay agents interact with DHCP clients and DHCP servers.  Hint:  It populates a field in the DHCP packet, changes the source to be it's own unicast IP, and changes the destination to be the remote DHCP server's unicast IP.
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Grant. . . .