CentOS - Mar 2016 - Is there a way to detect/validate DHCP static IP assignment?

Hi,
?We have tens of networks(VLANs) in data center with a central Linux DHCP
server. each network has their router to do the DHCP relay. So, the DHCP
server's configuration files has tens 'subnet' statements.
Because PXE booting is standard in whole data center, there are also thousands
of static MAC-IP mapping 'host' statements in dhcp configuration.
The big challenge with a central dhcp server is how to detect typo in the
thousands of MAC-IP 'host' statements? -- a single char/digit typo here
will fail a PXE booting or download wrong post-installation snippets.

?Is there a tool to validate all 'host' statements from another Linux
box?

I tried nagios check-dhcp plugin, with a series of real MAC addresses(for hosts
in other different networks). Surprisingly, the IP address came back were not
the static IP addresses in 'host' statement, but dynamic addresses in
the pool defined for this particular network (where I ran check-dhcp from).
check_dhcp was run with the following arguments:

/usr/lib64/nagios/plugins/check_dhcp --verbose --server=<my_dhcp_server>
--interface=eth0 --mac=<real_Mac_for_servers_in_diff_networks> --unicast
remove --unicast doesn't help but just see more DHCP replys.
Interestingly, with a same MAC address, and the above same command, from two
Centos boxes on different network there will be different dynamic IPs! instead
the static IP defined with 'host' statement.?

So, how can we validate static IP assignment? Thanks.
Best,David,

On 30/03/2016 18:08, David Copperfield wrote:
> Hi,
>   We have tens of networks(VLANs) in data center with a central Linux DHCP
server. each network has their router to do the DHCP relay. So, the DHCP
server's configuration files has tens 'subnet' statements.
> Because PXE booting is standard in whole data center, there are also
thousands of static MAC-IP mapping 'host' statements in dhcp
configuration.
> The big challenge with a central dhcp server is how to detect typo in the
thousands of MAC-IP 'host' statements? -- a single char/digit typo here
will fail a PXE booting or download wrong post-installation snippets.
>
>   Is there a tool to validate all 'host' statements from another
Linux box?
>
> I tried nagios check-dhcp plugin, with a series of real MAC addresses(for
hosts in other different networks). Surprisingly, the IP address came back were
not the static IP addresses in 'host' statement, but dynamic addresses
in the pool defined for this particular network (where I ran check-dhcp from).
> check_dhcp was run with the following arguments:
>
> /usr/lib64/nagios/plugins/check_dhcp --verbose
--server=<my_dhcp_server> --interface=eth0
--mac=<real_Mac_for_servers_in_diff_networks> --unicast
> remove --unicast doesn't help but just see more DHCP replys.
> Interestingly, with a same MAC address, and the above same command, from
two Centos boxes on different network there will be different dynamic IPs!
instead the static IP defined with 'host' statement.
>
> So, how can we validate static IP assignment? Thanks.
> Best,David,
>
Hi David,

You need to use check_dhcp_relayed.pl 
(https://github.com/timb07/check_dhcp_relayed) if you wish to test for a 
reservation outside of the servers subnet, otherwise the DHCP server 
will assume you are on the local range and issue from that subnet.

Also as an FYI Forman (http://theforeman.org) can do things like 
building VM's and Physical servers and integrates with DHCP to create 
static DHCP reservations for PXE booting servers which should eliminate 
typos.

Tris





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Hi tris,
?Many thanks, I'll give the perl script a try shortly....
Best,David 

    On Thursday, March 31, 2016 6:00 AM, Tris Hoar <trishoar at bgfl.org>
wrote:
 

 On 30/03/2016 18:08, David Copperfield wrote:
> Hi,
>? We have tens of networks(VLANs) in data center with a central Linux DHCP
server. each network has their router to do the DHCP relay. So, the DHCP
server's configuration files has tens 'subnet' statements.
> Because PXE booting is standard in whole data center, there are also
thousands of static MAC-IP mapping 'host' statements in dhcp
configuration.
> The big challenge with a central dhcp server is how to detect typo in the
thousands of MAC-IP 'host' statements? -- a single char/digit typo here
will fail a PXE booting or download wrong post-installation snippets.
>
>? Is there a tool to validate all 'host' statements from another
Linux box?
>
> I tried nagios check-dhcp plugin, with a series of real MAC addresses(for
hosts in other different networks). Surprisingly, the IP address came back were
not the static IP addresses in 'host' statement, but dynamic addresses
in the pool defined for this particular network (where I ran check-dhcp from).
> check_dhcp was run with the following arguments:
>
> /usr/lib64/nagios/plugins/check_dhcp --verbose
--server=<my_dhcp_server> --interface=eth0
--mac=<real_Mac_for_servers_in_diff_networks> --unicast
> remove --unicast doesn't help but just see more DHCP replys.
> Interestingly, with a same MAC address, and the above same command, from
two Centos boxes on different network there will be different dynamic IPs!
instead the static IP defined with 'host' statement.
>
> So, how can we validate static IP assignment? Thanks.
> Best,David,
>
Hi David,

You need to use check_dhcp_relayed.pl 
(https://github.com/timb07/check_dhcp_relayed) if you wish to test for a 
reservation outside of the servers subnet, otherwise the DHCP server 
will assume you are on the local range and issue from that subnet.

Also as an FYI Forman (http://theforeman.org) can do things like 
building VM's and Physical servers and integrates with DHCP to create 
static DHCP reservations for PXE booting servers which should eliminate 
typos.

Tris





*************************************************************
This email and any files transmitted with it are confidential
and intended solely for the use of the individual or entity 
to whom they are addressed. If you have received this email 
in error please notify postmaster at bgfl.org

The views expressed within this email are those of the 
individual, and not necessarily those of the organisation
*************************************************************
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