DHCP, ARP, RARP, PXE, ICMP, OSI, TMA

[Paul Lussier]

"Ben Scott" <dragonhawk at gmail.com> writes:

>   DHCP is implemented entirely in broadcast UDP [1].

Agreed.

> == RARP ==
>
>   RARP is a completely a different design vs DHCP/BOOTP.  RARP has the
> game goal as DHCP, in that RARP exists to let nodes without an IP
> address discover what their IP address should be.

Huh? Is that right?  I thought RARP allowed an IP addressless client
to broadcast it's MAC address to the network, at which point something
like a DHCP server would answer it...  But now that I think about it,
I think you're right, since the answering DHCP server is only going to
answer a properly formed DHCP packet, either DHCPDISCOVER or
DHCPREQUEST...  Okay, that makes sense, I got them all confused.

> However, RARP does not use UDP or anything else on top of, or
> within, the Internet Protocol itself.  RARP is implemented outside
> of the IP layer

Right, that I knew, and thought I mentioned.

> == PXE ==
>
>   PXE doesn't really have anything to do with DHCP directly.  PXE is
> just a standard network boot mechanism for the i386 IBM-PC
> architecture.

Yeah, and like everything else for the x86 architecture, a pretty
lousy one compared to what Sun, HP, and other proprietary HW vendors
have been using for years... :(

> I've never seen anything about PXE being able to use RARP, but then,
> nobody uses RARP these days, so maybe it's possible and just nobody
> cares.  :)

For some reason I thought PXE was build on RARP and that a DHCP server
could handle that.  But I've never read the PXE specs, so that is
probably a misunderstanding based on an ignorant assumption on my part
:)

> == ICMP ==
>
>   ICMP is implemented on top of the IP layer, along side the TCP and
> UDP layers.  All ICMP datagrams are IP datagrams, same as UDP or TCP.
> Other than their specific payload, there is nothing different about
> ICMP datagrams vs other IP datagrams.

This seems wrong to me.  I was fairly certain that ICMP was more a
peer with IP, and not build on top of it.  Wikipedia puts it at layer
3 *with* IP, for whatever that's worth.  Other references I've seen
state that it's "tightly integrated with IP", though what that means,
I'm not sure.  Since it requires IP addresses to function, and it is
transmitted using IP datagrams, I'll concede to agree for this
argument that's it built on top of IP :)

Do you have a decent reference for ICMP (other than the actual RFC) ?

> To avoid pedantic discussions like this one, it's best to 

not make any vague statements about anything, ever.  In fact, to avoid
pedantic discussions like this one, it's best to just unsubscribe from
the list right now! ;)
-- 
Seeya,
Paul