On Mon, 8 Apr 2024 23:30:04 -0500, Grant Taylor wrote:

> ... using the DHCP protocol across a routed network.

DHCP does not route. Somebody suggested looking at the actual RFC, which I
have done elsewhere. You should do it too.

On Tue, 9 Apr 2024 14:01:45 +0100, The Natural Philosopher wrote:

> Broadcast
>
> If you route broadcasts then all things are possible

The broadcast used in DHCP is 255.255.255.255, which is by definition not
routable.

On Tue, 9 Apr 2024 14:00:18 +0100, The Natural Philosopher wrote:

> I am not sure if the server issues an alternative or not.

The obvious answer is, it does if it has one, otherwise it doesn’t.

On Fri, 12 Apr 2024 20:22:33 -0500, Grant Taylor wrote:

> There are other aspects of DHCP that are routable. Like a DHCP helper /
> relay agent using the DHCP protocol to communicate with a remote DHCP
> server ...

DHCP is not routable, otherwise it wouldn’t need a helper to route it.

On Mon, 8 Apr 2024 23:42:48 -0500, Grant Taylor wrote:

> On 4/8/24 23:00, Lawrence D'Oliveiro wrote:
>
>> Like DECnet? But then you had to have a fixed relationship between your
>> MAC address and your DECnet address.
>
> Similar, but definitely not the same.

I didn’t say “same”.

> As in there was a direct algorithmic mapping between them.

So how would you run two simultaneous protocol stacks, each requiring its
own “algorithmic mapping” between MAC address and layer-3 address?

On Mon, 8 Apr 2024 23:51:21 -0500, Grant Taylor wrote:

> It's actually called a Gratuitous ARP, or GARP for short. GARP is a
> fairly common thing.

Ah. The World According To ...

... never mind.

(RIP Robin Williams.)

On 4/12/24 22:26, Lawrence D'Oliveiro wrote:
> The broadcast used in DHCP is 255.255.255.255, which is by definition not
> routable.

That's not the only (destination) address that DHCP uses.

On 4/12/24 22:30, Lawrence D'Oliveiro wrote:
> So how would you run two simultaneous protocol stacks, each requiring its
> own “algorithmic mapping” between MAC address and layer-3 address?

I was referring to the MAC address DECnet uses and the DECnet address.
There is an algorithmic relation ship between the MAC address a DECnet
station uses and it's DECnet address.

On 4/12/24 22:28, Lawrence D'Oliveiro wrote:
> DHCP is not routable, otherwise it wouldn’t need a helper to route it.

Yes, DHCP is routable.

Check out the very bottom graphic of the following URL:

https://support.huawei.com/enterprise/en/doc/EDOC1100112351/4b2f29de/how-a-dhcp-client-renews-its-ip-address-lease

Notice how the client sends a DHCP renew request to the DHCP server, not
the DHCP relay agent. It does this across a routed network.

The DHCP relay agent is only needed when the DHCP client doesn't have a
valid IP address and / or sends to the broadcast address.

When the client does have a valid IP address it uses routed unicast to
talk to the DHCP server using the very same DHCP protocol.

--
Grant. . . .

Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
>On Fri, 12 Apr 2024 20:22:33 -0500, Grant Taylor wrote:
>> There are other aspects of DHCP that are routable. Like a DHCP helper /
>> relay agent using the DHCP protocol to communicate with a remote DHCP
>> server ...
>
>DHCP is not routable, otherwise it wouldn’t need a helper to route it.

Repeating this doesnt make it right.

--
----------------------------------------------------------------------------
Marc Haber | " Questions are the | Mailadresse im Header
Rhein-Neckar, DE | Beginning of Wisdom " |
Nordisch by Nature | Lt. Worf, TNG "Rightful Heir" | Fon: *49 6224 1600402

On 13/04/2024 04:26, Lawrence D'Oliveiro wrote:
> On Tue, 9 Apr 2024 14:01:45 +0100, The Natural Philosopher wrote:
>
>> Broadcast
>>
>> If you route broadcasts then all things are possible
>
> The broadcast used in DHCP is 255.255.255.255, which is by definition not
> routable.

It is routable.

It's an 'all stations' broadcast.

You may choose not to route it, but that is not inherent in its qualities.

--
For in reason, all government without the consent of the governed is the
very definition of slavery.

Jonathan Swift

On Sat, 13 Apr 2024 09:04:55 +0100, The Natural Philosopher wrote:

> On 13/04/2024 04:26, Lawrence D'Oliveiro wrote:
>
>> The broadcast used in DHCP is 255.255.255.255, which is by definition
>> not routable.
>
> It is routable.
>
> It's an 'all stations' broadcast.

You need to go read some basic TCP/IP docs. Would you like me to point you
at some?

On Sat, 13 Apr 2024 00:40:12 -0500, Grant Taylor wrote:

> On 4/12/24 22:26, Lawrence D'Oliveiro wrote:
>
>> The broadcast used in DHCP is 255.255.255.255, which is by definition
>> not routable.
>
> That's not the only (destination) address that DHCP uses.

It can’t use any other, because remember, the client doesn’t have an
address that anybody can use, at this point.

On Sat, 13 Apr 2024 09:39:27 +0200, Marc Haber wrote:

> Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
>
>>DHCP is not routable, otherwise it wouldn’t need a helper to route it.
>
> Repeating this doesnt make it right.

I went through the details of RFC2131 in another posting. Go read it (the
RFC and my posting).

On Sat, 13 Apr 2024 00:42:38 -0500, Grant Taylor wrote:

> I was referring to the MAC address DECnet uses and the DECnet address.
> There is an algorithmic relation ship between the MAC address a DECnet
> station uses and it's DECnet address.

So how would you run two simultaneous protocol stacks, each requiring
its own “algorithmic relationship” between MAC address and layer-3
address?

On Sat, 13 Apr 2024 00:54:11 -0500, Grant Taylor wrote:

> Notice how the client sends a DHCP renew request to the DHCP server, not
> the DHCP relay agent. It does this across a routed network.

The only reason the relay agent is needed is because DHCP itself is not
routable.

On 4/14/24 19:47, Lawrence D'Oliveiro wrote:
> The only reason the relay agent is needed is because DHCP itself is not
> routable.

You're still wrong, on multiple accounts.

The DHCP agent is needed because at the time the client sends a DHCP
DISCOVER it's using 0.0.0.0 as it's source and sending to
255.255.255.255, which are not routed IPs.

And DHCP is routable, as I and others have told you.

I'm done telling you and going to start treating you like a troll.

--
Grant. . . .

On 4/14/24 19:42, Lawrence D'Oliveiro wrote:
> It can’t use any other, because remember, the client doesn’t have an
> address that anybody can use, at this point.

As I've told you multiple times, when a DHCP client /renews/ it's lease,
it has a valid IP address and can use that to talk to the DHCP server on
a remote subnet using standard DHCP protocol.

DHCP can be routed.

--
Grant. . . .

Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
> On Sat, 13 Apr 2024 09:39:27 +0200, Marc Haber wrote:
>
>> Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
>>
>>>DHCP is not routable, otherwise it wouldn’t need a helper to route it.
>>
>> Repeating this doesnt make it right.
>
> I went through the details of RFC2131 in another posting. Go read it (the
> RFC and my posting).

And, yet, you seem to have missed this statement from the RFC:

https://www.rfc-editor.org/rfc/rfc2131 - page 6:

DHCP should not require a server on each subnet. To allow for
scale and economy, DHCP must work across routers or through the
intervention of BOOTP relay agents.

Note they use "must" above in the statement "DHCP must work across
routers". Page 4 defines "must" as:

o "MUST"

This word or the adjective "REQUIRED" means that the item is an
absolute requirement of this specification.

Therefore the RFC explicitly allows for DHCP to be routed.

On 4/14/24 21:08, Rich wrote:
> Therefore the RFC explicitly allows for DHCP to be routed.

Nice find Rich. :-)

--
Grant. . . .

Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
>On Sat, 13 Apr 2024 00:40:12 -0500, Grant Taylor wrote:
>
>> On 4/12/24 22:26, Lawrence D'Oliveiro wrote:
>>
>>> The broadcast used in DHCP is 255.255.255.255, which is by definition
>>> not routable.
>>
>> That's not the only (destination) address that DHCP uses.
>
>It can’t use any other, because remember, the client doesn’t have an
>address that anybody can use, at this point.

"This point" being the start of the protocol. You should look beyond
the initial exchange.

--
----------------------------------------------------------------------------
Marc Haber | " Questions are the | Mailadresse im Header
Rhein-Neckar, DE | Beginning of Wisdom " |
Nordisch by Nature | Lt. Worf, TNG "Rightful Heir" | Fon: *49 6224 1600402

On 2024-04-15, Lawrence D'Oliveiro wrote:

> On Sat, 13 Apr 2024 09:04:55 +0100, The Natural Philosopher wrote:
>
>> On 13/04/2024 04:26, Lawrence D'Oliveiro wrote:
>>
>>> The broadcast used in DHCP is 255.255.255.255, which is by definition
>>> not routable.
>>
>> It is routable.
>>
>> It's an 'all stations' broadcast.
>
> You need to go read some basic TCP/IP docs. Would you like me to point you
> at some?

Why does it get called "TCP/IP" so often? What is the origin of that
name?

These are two different protocols for different layers and that name
does not include, say, UDP.

--
Nuno Silva

On 4/15/24 01:50, Nuno Silva wrote:
> Why does it get called "TCP/IP" so often? What is the origin of
> that name?

That's at lease partially becuase IPv1-3 was a single protocol. There
was lots of debating going on during the development of IPv1-3 for the
raw point to point that IP provides and in order delivery circuit that
TCP provides. It was part way through the development that the realized
that they could split IP into two layers TCP for end-to-end / in-order
delivery and IP for point to point connectivity that other protocols
could use.

> These are two different protocols for different layers and that name
> does not include, say, UDP.

IPv1-3 was split into TCP/IPv4. TCP was the first protocol that ran on
top of IPv4. I think part of the reason for the split name was to
emphasize the split protocol design.

I think UDP was officially documented within a year of TCP/IPv4 being
documented. But the progenitor of UDP existed before TCP/IPv4 was
documented. Experiments were ongoing with the parts of IPv3 that became
UDP/IP. Some of the experiments were for voice transmission.

--
Grant. . . .

On Mon, 15 Apr 2024 02:08:09 -0000 (UTC), Rich wrote:

> Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
>>
>> I went through the details of RFC2131 in another posting. Go read it
>> (the RFC and my posting).
>
> And, yet, you seem to have missed this statement from the RFC:
>
> https://www.rfc-editor.org/rfc/rfc2131 - page 6:
>
> DHCP should not require a server on each subnet. To allow for
> scale and economy, DHCP must work across routers or through the
> intervention of BOOTP relay agents.

No, I didn’t miss it at all. It’s listed under “design goals”, not
actually under how the spec works.

By definition such a protocol cannot work across routers, because clients
don’t know what routers are available until a DHCP server tells them.

Is there a section that describes which of the “design goals” were
actually met?

On Mon, 15 Apr 2024 08:01:12 +0200, Marc Haber wrote:

> Lawrence D'Oliveiro <ldo@nz.invalid> wrote:
>
>>On Sat, 13 Apr 2024 00:40:12 -0500, Grant Taylor wrote:
>>
>>> On 4/12/24 22:26, Lawrence D'Oliveiro wrote:
>>>
>>>> The broadcast used in DHCP is 255.255.255.255, which is by definition
>>>> not routable.
>>>
>>> That's not the only (destination) address that DHCP uses.
>>
>>It can’t use any other, because remember, the client doesn’t have an
>>address that anybody can use, at this point.
>
> "This point" being the start of the protocol. You should look beyond
> the initial exchange.

Once the protocol has done its thing, the client can do routable things.

At that point, it can stop worrying about DHCP for now.