[syslinux] Checking if host is on the same subnet

[Ady]

> Alexandre Blanchette <blanalex at gmail.com> writes:
> 
> > On Wed, Dec 10, 2014 at 10:14 AM, Ferenc Wagner <wferi at niif.hu> wrote:
> >
> >> Alexandre Blanchette <blanalex at gmail.com> writes:
> >>
> >>> We are doing a deployment across many sites, we're doing one site at
> >>> a time and we're bringing a "mobile server" (a laptop, really) to
> >>> keep traffic local instead saturating the WAN link of each site.
> >>>
> >>> I'd like to make a script so each client can determine if the mobile
> >>> server is on the same subnet either with a ping with a zero TTL
> >>> value, with the ip/netmask and a bit of binary logic, or any other
> >>> mean.
> >>>
> >>> Currently, PXELINUX is calling an iPXE script, so the solution can
> >>> be at either level.
> >>
> >> You should be able to do this via Lua and its DHCP module.  You will
> >> find partial documentation only, but for generic info see
> >> https://github.com/wferi/syslinux/blob/pub/com32/lua/doc/syslinux.asc
> >> (the loadfile and initramfs parts document a future plan) and
> >> https://github.com/wferi/syslinux/blob/pub/com32/lua/src/dhcp.c
> >> (but don't forget the dhcp = require "dhcp").
> >
> > Well, I'm missing a piece of the puzzle, I need to do a DNS lookup of
> > the mobile host. This is a "mobile" server, it doesn't have a static
> > IP.
> 
> And you always change its DNS record according to the current location?
> I thought its address was provided via DHCP to the clients.  Can't you
> arrange that?  Exporting Lua bindings to DNS functionality would also be
> feasible by patching Syslinux, but I'm somewhat confused by the PXE/lwIP
> duality here.  But for booting, DHCP should be enough, and if you need
> this decision after booting, then you've already got your operation
> system to help you.  What does this mobile server provide?
> -- 
> Regards,
> Feri.
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I'm not sure about this, but perhaps the SYSAPPEND directive could 
help?

 http://www.syslinux.org/wiki/index.php/Config#SYSAPPEND 

Regards,
Ady.