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From: Rich <rich@example.invalid>
Newsgroups: comp.os.linux.misc
Subject: Re: I never thought of this scenario
Date: Sat, 20 Apr 2024 19:07:43 -0000 (UTC)
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Marco Moock <mm+usenet-es@dorfdsl.de> wrote:
> On 20.04.2024 um 18:07 Uhr Rich wrote:
>> DHCP is also not a "transport layer" protocol.  Instead, it uses UDP 
>> for its transport layer (see RFC url above, page 22):
>> 
>>     "DHCP uses UDP as its transport protocol."
>> 
>> Since UDP is itself routable, DHCP is also routable, because DHCP is 
>> simply a protocol definition for sending particular "messages" 
>> inside of UDP packets.
> 
> That depends on the addresses being used.  When being used on 
> non-directed broadcast, link-local unicast or link-local multicast, 
> UDP can't be routed because the IP layer forbids routing of those 
> packages.

Yes, correct.  However, that is not "DHCP" the protocol itself 
specifying such.  That is the IP layer specifying that certian 
addresses used in UDP packets are not routed.

The reason it impacts DHCP is that the "bootstrap an IP address 
configuration" portion of DHCP means that those addresses are all the 
client can make use of until after it has been configured with a valid 
IP address for the local subnet.