[Etherboot-developers] Re: Choosing proper DHCP server at client side.

[Ken Y. <ke...@nl...>]

>Some DHCP servers have manual IP assignment configurations with client's
>MAC
>+address, but others have been configured as dynamic assignment scheme.
>So, if
>+there are any DHCP client, they can get one IP.
>
>This is useful when there are many mobile clients, but make it useless
>several
>+net-booted clients with manual MAC-based assign strategy. Because there
>are
>+"filename" directive for there own OS kernel image and other boot
>related
>+options, if they contact dynamic assignment DHCP server firstly, they
>can't
>+boot properly.

Etherboot already has the facility you are looking for, since 4.7.1x or
thereabouts. It consists of two parts:

Firstly all DHCPDISCOVER packets from Etherboot go out with the tag
Vendor Class Identifier (VCI is a tag defined in the DHCP RFC) of
"Etherboot-x.y" where x.y is the version number.

Secondly, if compiled with the conditional REQUIRE_VCI_ETHERBOOT,
Etherboot will only accept replies with the encapsulated option of the
tag VCI starting with "Etherboot". This is a compile time option because
if it were the default, then Etherboot would not be able to boot on a
plain setup.

The first is to allow a suitably configured DHCP server (e.g. ISC
DHCPD 3.0) to identify Etherboot clients and reply to only those, using
conditional scoping. This prevents the server from offering leases to
non-Etherboot clients.

The second is so that when more than one DHCPOFFER comes in, only the
one from the designated DHCP server will be accepted, offers from other
DHCP servers, presumably for booting other clients, will be ignored.

There are some short notes on this in RELNOTES, which need to migrate
into the main documentation when I get some time. It would be nice if
you could try the feature out, as I have not used it in production; I
have only verified that the components work.