2 IP addresses when PXE booting, ping check doesn't spot same MAC address

[Patrick Trapp]

In the instance I am referring to, the firmware identifies itself one way during the first boot and differently on the second boot, thus the different addresses. The first mode is strictly used for upgrading the system and is a minimal boot for that purpose.

But I digress from the original poster's issue. My apologies, carry on.

________________________________________
From: dhcp-users-bounces at lists.isc.org [dhcp-users-bounces at lists.isc.org] on behalf of Glenn Satchell [glenn.satchell at uniq.com.au]
Sent: Tuesday, October 21, 2014 9:11 AM
To: Users of ISC DHCP
Subject: RE: 2 IP addresses when PXE booting, ping check doesn't spot same      MAC     address

I do that with a PXE class in the server dhcpd.conf:

class "PXE" {
  match if substring(option vendor-class-identifier, 0, 9) = "PXEClient";
  next-server server.example.com.au;
  filename "pxegrub.I86PC.Solaris_10-1";
  # 10 minutes should be long enough for PXE
  max-lease-time 600;
}

But I agree with the OP, the server should recognise the same server
sending a DHCPDISCOVER and not abandon the lease. Maybe there is something
in the discover packet that makes it look a different client, even with
the option to ignore UID.

regards,
-glenn

On Wed, October 22, 2014 12:12 am, Patrick Trapp wrote:
> Perhaps I miss the point of the request, but I think we have a system that
> does something similar (as far as a two-stage boot). The first stage gets
> a very short lease (I'm not sure how) - is there a client option that
> would override (underride?) the server's default minimum lease time that
> you could utilize?
>
> Patrick
>
> ________________________________________
> From: dhcp-users-bounces at lists.isc.org [dhcp-users-bounces at lists.isc.org]
> on behalf of Stephen Borrill [dhcp-users at borrill.org.uk]
> Sent: Tuesday, October 21, 2014 5:32 AM
> To: dhcp-users at lists.isc.org
> Subject: 2 IP addresses when PXE booting, ping check doesn't spot same MAC
>      address
>
> I'm using a diskless system to boot Windows (Citrix Provisioning
> Services). This does a BIOS PXE boot, loads a bootstrap file from TFTP
> which connects to a virtual hard disk and then continues with the
> Windows boot as though it were a local disk. This means that the IP
> address acquired from the BIOS is inherited by Windows and remains in
> use. The interface within Windows is still set up to use DHCP and so it
> goes through its usual DHCP phase.
>
> It is common to end up with 2 IP addresses on the network when doing
> this. Initially the problem was that the BIOS does not send a UID with
> the request, but Windows does, so that dhcpd was treating them as two
> separate leases. I upgraded to v4.3.0 and used "ignore-client-uids true"
> to stop this. However, this then triggered another problem. At the time
> that Windows requests its IP address, the IP address from the PXE phase
> is still active as it cannot be released by the client. Therefore, the
> dhcpd ping check triggers, the original IP address is abandoned and a
> new IP address is picked:
>
> 10:44:32 dhcpd: DHCPDISCOVER from 36:06:41:1a:62:59 (pcmaster)
> 10:44:33 dhcpd: DHCPOFFER on 10.0.13.25 to 36:06:41:1a:62:59
> 10:44:35 dhcpd: DHCPREQUEST for 10.0.13.25 (10.0.0.1) from
> 36:06:41:1a:62:59
> 10:44:35 dhcpd: DHCPACK on 10.0.13.25 to 36:06:41:1a:62:59
> 10:47:18 dhcpd: DHCPDISCOVER from 36:06:41:1a:62:59
> 10:47:18 dhcpd: Abandoning IP address 10.0.13.25: pinged before offer
> 10:47:20 dhcpd: DHCPDISCOVER from 36:06:41:1a:62:59
> 10:47:21 dhcpd: DHCPOFFER on 10.0.19.232 to 36:06:41:1a:62:59 (pcmaster)
> 10:47:21 dhcpd: DHCPREQUEST for 10.0.19.232 (10.0.0.1) from
> 36:06:41:1a:62:59 (pcmaster)
> 10:47:21 dhcpd: DHCPACK on 10.0.19.232 to 36:06:41:1a:62:59 (pcmaster)
>
> (slightly edited to remove extraneous information such as date, hostname
> and interface name)
>
> To test this theory, setting "ping-check false" allows the machine to
> keep its single initial address.
>
> It seems to me that there should be an option to only abandon an IP
> address after a ping check if the MAC address that responds does not
> match the requester. Any other suggestions?
>
> --
> Stephen
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