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From: The Natural Philosopher <tnp@invalid.invalid>
Newsgroups: comp.os.linux.misc
Subject: Re: I never thought of this scenario
Date: Mon, 22 Apr 2024 11:36:54 +0100
Organization: A little, after lunch
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On 22/04/2024 09:30, Marc Haber wrote:
> The Natural Philosopher <tnp@invalid.invalid> wrote:
>> 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..
>>
>> 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.
>> In short its acting like an ethernet switch or bridge
>>
>> 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. :-)
> 
> That's because the DHCP relay agent does not simply "route" the
> broadcast packet, it generates a new packet with the client message,
> adds information about itself (such as, for example, the IP address of
> the Interface where the DHCP broadcast was received on) and forwards
> the resulting NEW message as routable unicast to the DHCP server.
> 
I.e it does a bit of address translation,  like NAT. It messes with the 
return address as well as the destination addrress

-- 
How fortunate for governments that the people they administer don't think.

Adolf Hitler