Re: I never thought of this scenario

Grant Taylor <gtaylor@tnetconsulting.net> 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.

In a way, yes, given that HTTP/NNTP are also not "transport layer
protocols".  Their routability is determined by the routability of the
transport layer packet carrying them (which would be IP for both).

It is a somewhat atypical way of viewing the definition of "routing",
but it does match what is actually happening in routers.  Exclusive of
"deep packet inspection" a router is routing packets by looking at the
IP header of that packet, not looking inside the IP packet's payload
for HTTP/NNTP/DHCP/etc.  contents and routing based on those contents.

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.

True, that is actually where the "routing" decision is made.