Re: [gentoo-user] Be careful when using dhcp with a LiveCD

[Mick]

On Friday 07 December 2007, b.n. wrote:
> Mick ha scritto:
> >> The point is: be careful when using dhcp from a LiveCD.  Your system
> >> might act differently the next time you boot the hard drive.
> >
> > The dhcpcd was changed recently and not all dhcp servers take kindly to
> > it, when it uses DUID the way it does (some servers depend on DUID
> > passing on to them the MAC of the client).  The solution I also found was
> > to set the vram flag.
>
> I'm really ignorant on networks. What has changed on the dhcp side so
> that *client* behaviour alters *server* behaviour? Isn't this horribly
> broken (from the server side), or there is some reason to behave that?

I am no less ignorant I'm afraid, but this is how I understand it in simple 
terms:

net-misc/dhcpcd-3.1.5-r1 has introduced a usage of DUID which is compliant 
with RFC 4361, and creates a client ID (this can be any string uniquely 
identifying the client interface).  However, a number of DHCP server 
implementations expect the DUID to contain the MAC of the client and unless 
this is in a particular format the server falls over.

The vrm flag allows the MAC to be used in the DUID field and then the server 
is happy to issue an IP address to the client.  As an alternative one can try 
the dhcpcd -I option to specify the MAC of the client, but when I tried it I 
couldn't get it to work.

I guess eventually all dhcp implementations will catch up with this change, 
although for now it is bound to create some problems with particular DHCP 
servers (cisco being one of them).  On the other hand RFC 4361 may be 
superseded/reversed, dhcpcd will go back to how it was and the world will be 
a simpler place to live and network.  :)

HTH.
-- 
Regards,
Mick