Set DHCP Reservations in a Windows DHCP server from a Linux node

dhcpwindows-server-2008

I have a nice set up in my unixland where I have all my host information (names, IPs, mac addresses) in DNS and the associated NIS maps. This makes it easy to write a script which can generate a file containing DHCP lease reservation information, which can then be included by the isc dhcpd.conf for each scope. This means whenever a system is booted, it always gets the same IP whether it is static or not, and can figure out its DNS name trivially. This means for example that when I kickstart nodes, the post-install scripts can do host-specific things based on what name the system finds for itself at install time.

Now I'm being assimilated by a new organization, and their infrastructure runs on Windows. I am about to receive my brand new Windows DC, which will be the site's DNS and DHCP server.

So. Is there a way to put DHCP reservations in the new DHCP server, without having to do it manually?

Update:

So how this works in unix is that for each machine on my subnet, I can (effectively) do this:

$ ypmatch $MACHINE hosts
$ ypmatch $MACHINE ethers

…and generate a file full of entries like this:

host amstel
{
    hardware ethernet 00:04:76:f8:d8:71;
    option host-name "amstel";
    fixed-address 10.16.5.23;
}

…the filename of which is included in my dhcpd.conf as so:

subnet 10.16.0.0 netmask 255.255.240.0
{
...
        # Include automatically-generated reservations
        include "/etc/dhcpd-10.16.0.0-20.conf";    
}

Then whenever I make an update, all I have to do is run the updater script and restart dhcpd.

So. Starting from the ypmatch ... what can I run on unixland that will insert this kind of reservation into a Windows DHCP server?

Best Answer

You can manuipulate DHCP using netsh. Using the DHCP server named srv1, add a reservation for computer named clientA.domain.lan, with MAC 00FF00FF00FF, to the scope 192.168.0.0:

netsh dhcp server srv1 scope 192.168.0.0 add reservedip 192.168.0.101 00FF00FF00FF clientA.domain.lan

You can do much more than DHCP with netsh. Typing netshenter in a Windows commmand prompt will switch you to the netsh context. The help command will display available options.

Related Solutions

Centos – modify dhcpd.conf via script to convert whole subnet to DHCP reservations

I suppose you are using ISC DHCPd. In this case just add

host client_name {
    hardware ethernet 00:00:de:ad:be:ef;
    fixed-address 10.10.10.100;
}

to your scope in /etc/dhcpd.conf.

Of course, you would not "hand-edit" this but rather create a short script that would spit out the necessary host definitions per scope. Something like that would do:

#!/bin/bash
function hostdef {
        echo host $1 {
        echo -e \\thardware ethernet $2\;
        echo -e \\tfixed-address $3\;
        echo }
        echo
}

cat $1 | while read name mac ip; do hostdef $name $mac $ip; done

calling it with a flat file with contents like this:

ip-100 00:00:de:ad:be:ef 10.10.10.100
ip-101 00:00:0b:ad:be:ef 10.10.10.101
ip-102 00:00:0b:ad:de:ed 10.10.10.102
ip-103 00:00:de:af:be:ef 10.10.10.103

would generate the necessary lines to paste into your config file or write the output to a separate file which you would include in your dhcpd.conf configuration like this:

include "/etc/dhcpd-reservations-10-10-10.conf";

Debian – DHCP Server with multiple network interfaces and different subnets

So here we go with a little explanation what happens. PLEASE note that I would strongly advise to run the configurations inside a testing environment to make sure, everything works as you want it to!

Edit: Please also note that your switches need to be properly configured. We are using CISCO switches. To generate an OMAPI Key, you can follow guide1 or guide2.

How to make isc-dhcp-server listen on mulitple subnets. This mini-guide will give you a basic configuration idea and some additional material to read to fully understand what's going on.

dhcpd.conf:

omapi-port 7911;
omapi-key omapi_key;

key omapi_key {
     algorithm hmac-md5;
     secret your-secret-key;
}

# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed. We default to the
# behavior of the version 2 packages ('none', since DHCP v2 didn't
# have support for DDNS.)
ddns-update-style none;

# option definitions common to all supported networks...
# option domain-name-servers x.x.x.x,y.y.y.y;
option netbios-node-type 2;

default-lease-time 7200;
max-lease-time 7200;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

# Failover Configuration

failover peer "failover-partner" {
        primary;
        # this servers ip address
        address A.A.A.A;
        port 519;
        # dhcp failover ip address
        peer address B.B.B.B;
        peer port 520;
        max-response-delay 60;
        max-unacked-updates 10;
        mclt 3600;
        split 128;
        load balance max seconds 3;
}

# No service will be given on this subnet, but declaring it helps the
# DHCP server to understand the network topology.

# here we include specific configuration files for our different subnets.
# I'll provide an example for a configuration file, all other subnet configuration files
# are (in my scenario) written the same way.

include "/etc/dhcp/X.Y.1.Z.conf";
include "/etc/dhcp/X.Y.2.Z.conf";
include "/etc/dhcp/X.Y.3.Z.conf";

X.Y.1.Z.conf:

#____________________________________
# subnet information  X.Y.1.0/24
#____________________________________
subnet X.Y.1.0 netmask 255.255.255.0 {
        deny client-updates;
        deny unknown-clients;
        # gateway of this subnet  
        option routers X.Y.1.254;
        # DNS server(s)
        option domain-name-servers 123.123.123.1, 123.123.123.2;
        # search domain(s) for this subnet. Needs the "" to work!
        option domain-search "domain1", "domain2";
        # name of domain of this subnet (if exists, otherwise comment out)
        option domain-name "mydomain";
        # ntp server if you are running one
        option ntp-servers X.Y.Z.254;
        default-lease-time 86400;
        max-lease-time 86400;

        group {
            use-host-decl-names on;

            # Infodisplay
            host dns-name-1 {
            # mac address of client
                hardware ethernet 00:00:00:00:00:00;
            # ip address the above mac address will receive
                fixed-address 123.123.123.1;
            }
       }

Other configuration files for subnets are built equally. Be sure, if you run a DHCP VM inside ESXi, to make the VM available to all your networks / VLANs. The isc-dhcp-server then needs to listen on all networks it's expected to so it can handle differen subnets all within one running instance of isc-dhcp-server. If you want to omit downtime or a non working network, you can of course run a second VM with isc-dhcp-server in slave mode like this:

slave dhcpd.conf:

omapi-port 7911;
omapi-key omapi_key;

key omapi_key {
     algorithm hmac-md5;
     secret your-secret-key;
}

# The ddns-updates-style parameter controls whether or not the server will
# attempt to do a DNS update when a lease is confirmed. We default to the
# behavior of the version 2 packages ('none', since DHCP v2 didn't
# have support for DDNS.)
ddns-update-style none;

# option definitions common to all supported networks...
# option domain-name-servers x.x.x.x,y.y.y.y;
option netbios-node-type 2;

default-lease-time 7200;
max-lease-time 7200;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

# Failover Configuration

failover peer "failover-partner" {
        primary;
        # this servers ip address
        address B.B.B.B;
        port 519;
        # dhcp master ip address
        peer address A.A.A.A;
        peer port 520;
        max-response-delay 60;
        max-unacked-updates 10;
        mclt 3600;
        split 128;
        load balance max seconds 3;
}

# No service will be given on this subnet, but declaring it helps the
# DHCP server to understand the network topology.

# here we include specific configuration files for our different subnets.
# I'll provide an example for a configuration file, all other subnet configuration files
# are (in my scenario) written the same way.

include "/etc/dhcp/X.Y.1.Z.conf";
include "/etc/dhcp/X.Y.2.Z.conf";
include "/etc/dhcp/X.Y.3.Z.conf";

Make sure the secret keys are the same on both machines, otherwise client and server are not able to communicate or to even do a failover switch if server fails and slave is expected to take over the dhcp-functionality.

If you have the hardware/setup options, please setup all this in an experimental environment.

PLEASE DO NOT INSTANTLY RUN THIS IN A PRODUCTION ENVIRONMENT.

You can stop making your network clients work within seconds and that's what your boss will not like.

Best Answer

Related Solutions

Centos – modify dhcpd.conf via script to convert whole subnet to DHCP reservations

Debian – DHCP Server with multiple network interfaces and different subnets

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