[syslinux] Etherboot & pxelinux (was: thank you)

H. Peter Anvin hpa at zytor.com
Thu Feb 7 14:12:33 PST 2002


Peter Lister wrote:

> 
> Granted; my point is that we (Sychron) have crossed over into the realm
> of getting our hands dirty with DHCP anyway, and we need to maintain a
> server side db of all our hardware; we do clusterwide resource control,
> so how a node should boot is all tied in with e.g. speed, memory rather
> than it's NICs MAC address, so it makes sense to do so in one place.
> This is an argument for better a DHCP server which can create options on
> the fly.
> 
> pxelinux's ability to have different configs based on IP address is
> neat, but I really want choices based on arbitrary information (e.g.
> hardware that is aware of the rack/chassis/slot where it lives) - we
> also may have systems with no fixed IP address.
> 


Please do note that PXELINUX can have the config file specified or even
synthesized by the DHCP server.  If you really want to do DHCP-centric
configuration you can do it by specifying abstract configuration.

The IP-based default is a convenience, but isn't the only option.

> Likewise, when asked about preferring DHCP to a config file it seemed
> reasonable to explain why (issues of ISC dhcpd apart) DHCP seems to be a
> much better long term solution. For what it's worth, I think that
> Etherboot's DHCP could do with restructuring.


I would have to disagree with that.  DHCP has a fair number of problems,
one of them being that you simply can't specify abitrary amounts of data,
since it needs to fit in a single UDP packet *and* fit in the buffers on
the target system -- in practice (meaning: this is how real life
implementations work, like it or not) that means it has to fit in an
single Ethernet packet.  A configuration file can be arbitrarily long.

There is also the particular issue with Etherboot that it interprets just
about the entire site-specific set of codes as its own, without having any
kind of magic key or anything.  PXELINUX has a pretty small set (what it
needs *before* the configuration file loads) of site-specific codes, and
they're keyed.  You basically has to do something like that, especially in
a PXE environment.

	-hpa





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