dhcp server - only supply options, not address
I have isc-dhcp-server running on my router, and it currently supplies info needed for booting diskless devices (mythtv boxes, etc). The actual booting takes place on my server though, and I want the server to supply the dhcp options rather than the router, but still want the router to supply the address etc. This is so I am only editing this stuff in one place, and can script the configuration depending on how I want to boot (boot direct to iscsi with an iscsi filename, or chain via pxelinux where required, etc). I think this is possible, and I've definitely done it before in a Windows environment with WDM, but I can't find the magic incantation for the secondary dhcp server so it will supply options even though it shouldn't supply the lease. Any suggestions? Thanks James
Hi James This is way out of my skill range so this might be an absurd suggestion but here goes. If your server had zero addresses in the pool would a computer pass onto the isc-dhcp-server or would it loop? Cheers Nic On 20/09/15 11:08, James Harper wrote:
I have isc-dhcp-server running on my router, and it currently supplies info needed for booting diskless devices (mythtv boxes, etc).
The actual booting takes place on my server though, and I want the server to supply the dhcp options rather than the router, but still want the router to supply the address etc. This is so I am only editing this stuff in one place, and can script the configuration depending on how I want to boot (boot direct to iscsi with an iscsi filename, or chain via pxelinux where required, etc).
I think this is possible, and I've definitely done it before in a Windows environment with WDM, but I can't find the magic incantation for the secondary dhcp server so it will supply options even though it shouldn't supply the lease.
Any suggestions?
Thanks
James _______________________________________________ luv-main mailing list luv-main@luv.asn.au http://lists.luv.asn.au/listinfo/luv-main
On Sun, Sep 20, 2015 at 01:08:36AM +0000, James Harper wrote:
I have isc-dhcp-server running on my router, and it currently supplies info needed for booting diskless devices (mythtv boxes, etc).
The actual booting takes place on my server though, and I want the server to supply the dhcp options rather than the router, but still want the router to supply the address etc.
i have no idea how to do what you want but i'm wondering why you want to do that. you are running a perfectly capable dhcp server on your router, so why not just write your script to generate the complete config file and push it to the router with scp or whatever? in my experience, two "unsynchronised" dhcp servers on a network just causes trouble. weird, seemingly random, difficult to trouble-shoot trouble. craig ps: remember to restart the router's dhcpd (e.g. with ssh) after updating the config. isc-dhcp-server doesn't automatically notice its config has changed, nor does it interpret a HUP signal to mean reload conf. pps: if you can't use ssh or scp, you could use possibly use curl or wget to update the dhcpd config via the router's web interface. -- craig sanders <cas@taz.net.au>
The actual booting takes place on my server though, and I want the server to supply the dhcp options rather than the router, but still want the router to supply the address etc.
i have no idea how to do what you want but i'm wondering why you want to do that.
you are running a perfectly capable dhcp server on your router, so why not just write your script to generate the complete config file and push it to the router with scp or whatever?
in my experience, two "unsynchronised" dhcp servers on a network just causes trouble. weird, seemingly random, difficult to trouble-shoot trouble.
In this case I have control of the DHCP server so that would work, but in other cases I might not. Things would work much more smoothly if the second DCHP server could respond to requests for the options it knows about. But as you suggested, I am just pushing it all out from the primary now. Thanks James
James Harper <james@ejbdigital.com.au> wrote:
I have isc-dhcp-server running on my router, and it currently supplies info needed for booting diskless devices (mythtv boxes, etc).
The actual booting takes place on my server though, and I want the server to supply the dhcp options rather than the router, but still want the router to supply the address etc. This is so I am only editing this stuff in one place, and can script the configuration depending on how I want to boot (boot direct to iscsi with an iscsi filename, or chain via pxelinux where required, etc).
Technically, I think you can do this with IPv6 by allowing the client devices to obtain their addresses from router advertisements while supplying other options via DHCPv6. Unfortunately, this own't help you, as the firmware of your devices supports IPv4 only.
On Sun, 20 Sep 2015 01:08:36 AM James Harper wrote:
The actual booting takes place on my server though, and I want the server to supply the dhcp options rather than the router, but still want the router to supply the address etc. This is so I am only editing this stuff in one place, and can script the configuration depending on how I want to boot (boot direct to iscsi with an iscsi filename, or chain via pxelinux where required, etc).
Having a quick look at the protocol I don' t think it's possible as DHCPOFFER's MUST include an IP address for the client, the client can only select one offer to use and the RFC says: Once the network address and lease have been determined, the server constructs a DHCPOFFER message with the offered configuration parameters. It is important for all DHCP servers to return the same parameters (with the possible exception of a newly allocated network address) to ensure predictable client behavior regardless of which server the client selects. The configuration parameters MUST be selected by applying the following rules in the order given below. The network administrator is responsible for configuring multiple DHCP servers to ensure uniform responses from those servers. The clients could be configured to do a DHCPINFORM though to request parameters and the servers DHCPACK responses could have that information. Best of luck! Chris -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC
participants (5)
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Craig Sanders -
James Harper -
Jason White -
Nic Baxter