dhcp server monitoring via NAGIOS

[sthaug at nethelp.no]

>            I'm trying to monitor a DHCP server from Nagios.Issue is my DHCP 
> server doesn't have any subnets defined in which Nagios operates.I have 
> tried NRPE plugin to run on DHCP server but in vain.Is there any other 
> way to monitor my DHCP server.

You're making this way too complicated.

All you need is for the DHCP server to know about a network where the
Nagios server can *reach* the DHCP server. The DHCP server does *not*
need to actually hand out addresses on this network. The network can
be *one single adress* (the address of the Nagios server itself).

So for instance, using a lightly anonymized example from own config:

subnet 193.69.x.y netmask 255.255.255.255 {}

Notice the contents part of the actual subnet declaration is empty.

Here is tcpdump output from such a transcation (DHCPINFORM from the
monitoring server, in our case a different system than Nagios):

11:39:17.577320 IP (tos 0x0, ttl 118, id 280, offset 0, flags [none], proto UDP (17), length 576) 193.69.x.y.68 > 193.75.p.q.67: BOOTP/DHCP, Request from 00:15:5d:0e:47:d1, length 548, xid 0x1a, Flags [none]
          Client-IP 193.69.x.y
          Client-Ethernet-Address 00:15:5d:0e:47:d1
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message Option 53, length 1: Inform
11:39:17.577519 IP (tos 0x0, ttl 64, id 40096, offset 0, flags [none], proto UDP (17), length 328) 193.75.p.q.67 > 193.69.x.y.68: BOOTP/DHCP, Reply, length 300, xid 0x1a, Flags [none]
          Client-IP 193.69.x.y
          Client-Ethernet-Address 00:15:5d:0e:47:d1
          Vendor-rfc1048 Extensions
            Magic Cookie 0x63825363
            DHCP-Message Option 53, length 1: ACK
            Server-ID Option 54, length 4: 193.75.p.q
            Subnet-Mask Option 1, length 4: 255.255.255.255
            Domain-Name-Server Option 6, length 8: 193.75.75.75,193.75.75.193
            T252 Option 252, length 2: 2560
            NTP Option 42, length 8: 193.71.1.10,193.71.1.20

Steinar Haug, Nethelp consulting, sthaug at nethelp.no