[mythtv-users] Questions on PXE booting a frontend

[Brian Wood]

On Monday 03 August 2009 17:25:08 Michael Cook wrote:
> Brian Wood <beww at beww.org> writes:
> > On Monday 03 August 2009 13:04:18 Ronald Frazier wrote:
> >> I too have had no problem letting my myth backend run dhcp for the
> >> diskless frontend systems and letting my router handle dhcp for
> >> everything else. My dhcpd.conf file is similar to Jelte's, but there
> >> are a few differences. Here is what I have. Don't ask my why I did
> >> things any specific way. I just copied setting from some tutorials and
> >> adjusted accordingly.
> >
> > If it's working I wonder if it is because of luck. Perhaps one of
> > the machines takes a lot longer to respond to a DHCP request or
> > some other mechanism is preventing both dhcp servers from trying
> > to work at the same time, or they are sufficiently stubborn to try
> > again when they get interfered with, and the retry intervals are
> > sufficiently different to prevent collision (not "collision" in
> > the ethernet sense, but in the "two dhcp servers trying to work at
> > the same time" sense).
> >
> > The conventional wisdom is that more than one dhcp server on a
> > network is asking for trouble.
>
> Well, the protocol was designed to allow multiple DHCP servers on
> the same broadcast medium.  But it's possible that doing so would
> uncover bugs in one or another DHCP server.  (Years ago I
> encountered a DHCP server that would leak a little memory each time
> it saw traffic from another DHCP server, and the leaky server wouuld
> eventually crash when it ran out of memory.)
>
> FWIW, the protocol is:
>
> 1. client: DISCOVER ("Is there anybody out there?")
> 2. server: OFFER ("You could ask for this here lease, if you wish")
> 3. client: REQUEST ("Okay, give me this here lease")
> 4. server: ACK ("You got it")
>
> When the client sends a DISCOVER and there are multiple DHCP
> servers, the client might get multiple OFFERs, but the client would
> send only one REQUEST (and would let the other OFFERs will expire).
>
> FWIW, I've been running two DHCP servers on my home network for
> years.  One is my Vonage Linksys router, and the other is my mythtv
> backend.  (I've configured them to use non-overlapping ranges of IP
> addresses within the subnet, but I think that's not strictly
> necessary.)

Probably not. Most DHCP servers will ping an address and not assign it if 
anything responds.

But you could still get into trouble I guess, if the timing of things was 
precisely right (or wrong).



-- 
Brian Wood
beww at beww.org