Conflicts and network boot

[Glenn Satchell]

Hi Bruno,

There's a clue in the output from dhcpd: it ignores the request for an
address it doesn't know about because the server is not
"authoritative". This is the default behaviour. To change this add a
statement at the top of the file before the group or perhaps in the
subnet definition:

  authoritative;

This is from the man page dhcpd.conf:

     If the server knows nothing about  the  address,
     it  will  remain silent, unless the address is incorrect for
     the network segment to which the client  has  been  attached
     and the server is authoritative for that network segment, in
     which case the server will send a  DHCPNAK  even  though  it
     doesn't know about the address.

Also see the part that starts with

     The authoritative statement

in the same man page for some discussion on whether to have global or
subnet scope for authoritative.

regards,
-glenn

>Date: Fri, 17 Mar 2006 19:13:02 -0300
>From: "Bruno Gola" <brunogola at gmail.com>
>To: dhcp-users at isc.org
>Subject: Conflicts and network boot
>
>Good night (here in Brazil) everyone :-)
>I'm new to the mailing-list and to dhcpd, and i'm already having problems ;(
>
>The situation is: iin my office we have a dhcp server (that i dont have
>access to)  that controls all machines. But, i need to netboot some
>machines. 'till yesterday i was able to do this using bootp, pxelinux and
>tftp, but we have a new machine and this one cant use bootp for this task,
>so i need to migrate my bootp server to dhcp (what i've already did). The
>machine that was booting with the bootp server, now is booting with the dhcp
>(wich i set up for allowing bootp requests) fine, but my new machine doesn't
>boot. Take a look at this log:
>
>#####
>Mar 17 18:24:40 dostoieviski dhcpd: DHCPDISCOVER from 00:0c:29:88:3d:eb via
>eth0                    <--- this is my new machine trying
>Mar 17 18:24:40 dostoieviski dhcpd: DHCPOFFER on 172.16.7.206 to
>00:0c:29:88:3d:eb via eth0     <---- this is my new dhcp server
>Mar 17 18:24:42 dostoieviski dhcpd: DHCPREQUEST for 172.16.200.113 (
>172.16.0.1) from 00:0c:29:88:3d:eb via eth0: ignored (not
>authoritative).                                   172.16.0.1 is the
>principal dhcp server
>#####
>
>and look this (i've used snort to see)
>
>
>03/17-18:24:40.198628 0.0.0.0:68 -> 255.255.255.255:67
>(the machine sending a DHCPDISCOVER)
>UDP TTL:20 TOS:0x0 ID:0 IpLen:20 DgmLen:576
>Len: 548
>=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
>
>03/17-18:24:40.202439 172.16.0.1:67 -> 255.255.255.255:68
>(the old dhcp server replying)
>UDP TTL:128 TOS:0x0 ID:4271 IpLen:20 DgmLen:376
>Len: 348
>=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
>
>03/17-18:24:40.210248 172.16.7.101:67 -> 255.255.255.255:68
>(my new dhcp server)
>UDP TTL:64 TOS:0x10 ID:0 IpLen:20 DgmLen:328
>Len: 300
>=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
>
>--
>03/17-18:24:42.280418 0.0.0.0:68 -> 255.255.255.255:67
>UDP TTL:20 TOS:0x0 ID:1 IpLen:20 DgmLen:576
>Len: 548
>=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
>
>03/17-18:24:42.281635 172.16.0.1:67 -> 255.255.255.255:68
>UDP TTL:128 TOS:0x0 ID:4307 IpLen:20 DgmLen:395
>Len: 367
>=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
>
>I think the old dhcp server cant handle bootp stuff, so thats why my old
>machine can boot, but my new machine uses dhcp, so the old server conflicts
>with my new server and the client gets information from the old one.
>
>my dhcpd.conf:
>
>group {
>        allow booting;
>        allow bootp;
>
>        option domain-name "eversystems.net";
>        option routers 172.16.1.254;
>        option subnet-mask 255.255.0.0;
>        option domain-name-servers 172.16.0.1;
>
>        next-server 172.16.7.101;
>        filename "pxelinux.0";
>
>        host tchekov {
>                hardware ethernet 00:14:22:7A:7D:3C;
>                fixed-address 172.16.7.202;
>        }
>
>        host pushkin {
>                hardware ethernet 00:12:3F:76:83:94;
>                fixed-address 172.16.7.204;
>        }
>
>        host testebgola {
>                hardware ethernet 00:0C:29:88:3D:EB;
>                fixed-address 172.16.7.206;
>        }
>}
>
>subnet 172.16.7.0 netmask 255.255.255.0 {
>
>}
>
>Does anyone knows anyway to solve this conflict?
>
>Thanks and sorry my english =),
>--
>Bruno Fialho Marques Gola <brunogola at gmail.com>
>http://www.brunogola.com.br
>Cel: (11) 9294-5883
>
>