Re: I never thought of this scenario

On 20/04/2024 21:16, Grant Taylor wrote:

On 4/20/24 14:19, Rich wrote:

DHCP the protocol is itself is not routable -- because DHCP the protocol is not a transport layer protocol.  It relies upon UDP for its transport.

 Given that logic, HTTP(S) and NNTP(S), both of which are dependent on TCP, which is dependent on IP, aren't routable either.
 

And whether a given DHCP message is routed or not is wholly dependent upon whether the UDP packet carrying the DHCP message is itself routable.

 I believe you want to go another layer and say that the UDP datagram is dependent on the IP packet carrying it.  And the IP packet's routability is dependent on it's source IP and if there is a route to the destination IP or not.
 }:-)
 

Is a destination address of 255.255.255.255 routable?
Of course it is, if a router is configured to do an 'all stations broadcast' across the internet!
What changes is that the client which has no IP address at this stage, instead has to be given one by the first router it encounters. When the router receives a response it has to translate that back to the MAC address of the sender  on its local port.
It's not much different from address translation, in that the router needs to exercise intelligence about some packet contents, rather  than juts their source and destination  and next hop addresses.
AS far as intelligence goes its nothing like as complex as running BGP or OSPF or  other routing protocols.
Calling this action a 'relay agent' makes it all into something it is not - a separate addition to routers in general.  DHCP can be and is routed by routers.
The rest is semantics
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