dhcpsync.8(8)

NAME

dhcpsync - synchronize DHCP configuration file

SYNOPSIS

[ KEY=keyfile ] [ SHARED=/path/to/conffile ] [ SLEEP=sec
onds ] dhcpsync <hostname of slave>

DESCRIPTION

This script shows how to detect if the dhcpd configuration
has changed, and sync a shared conf file to the slave, and
restart both servers.

o It is run on the master failover peer

o It uses rsync over ssh with an enforced command on the

slave.

o It relies on all include files being mentioned in

"DHCPD_CONF_INCLUDE_FILES" in /etc/rc.con
fig.d/dhcpd.rc.config. These files are looked at to
find out whether one of the config files is newer than
dhcpd's pid file ('rcdhcpd probe')

dhcpsync should actually be usable without modification. But you need to do some configuration, read on.

CONFIGURATION

In this example, host1 is the master, host2 is the slave.

A key can be generated like this: (save the key in
/root/.ssh/dhcp-share, and press enter when asked for the
passphrase.)

root@host1 ~ # ssh-keygen -C 'dhcp-share@host1'
Generating public/private rsa1 key pair.
Enter file in which to save the key (/root/.ssh/identi

ty):

/root/.ssh/dhcp

share

Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/dhcp

share.
Your public key has been saved in /root/.ssh/dhcp

share.pub.
The key fingerprint is:
21:11:ec:20:00:42:2f:20:7e:1f:df:6a:d1:25:3d:81 dhcp

share@host1
root@host1 ~ #

Now you add the key to the authorized_keys file on the
slave (host2):

root@host1 ~ # cat ~/.ssh/dhcp-share.pub | ssh

root@host2 'mkdir -p .ssh; cat >> .ssh/autho

rized_keys'

(This will append the key to an existing authorized_keys
file, or create one.)

To protect the root account (you could as well use another
account, of course), you can edit .ssh/authorized_keys on
host2 like this: (Thereby, only the forced command can be
executed, and only from host1.)

from="host1",command="rsync --server -vlogDtprc .

/etc//dhcpd.con
f.shared; logger dhcpsync: restarting dhcpd;

/etc/init.d/dhcpd re
start",no-port-forwarding,no-X11-forwarding,no-agent

forwarding,n
o-pty 1024 35

153745022190516820299391088867549182186599040623906
39933745099888497383649196106925140349057243770084885129581786366
05465027720474718409180919631615923416064825206960144541025646589
06475280304001588034598721095438582948133259768243300555751330261
946744924207972755699883176592160263892584211118353855811030877

d
hcp-share@host1

To run dhcpsync, you must specify the hostname of the "SLAVE" by putting it into the environment,

root@host1 ~ # SLAVE=host2 dhcpsync

or, alternatively, giving the name as the first argument:

root@host1 ~ # dhcpsync host2

CHANGING THE DEFAULTS

Please refer to the FILES section to see what the defaults
are.

The name of the file to be synced can be overridden from
the environment (bash example):

root@host1 ~ # SHARED="some_other_file" dhcpsync host2

Likewise, the ssh key to be used to authenticate can be
specified via the "KEY" variable.

AUTOMATION

The script can be run from cron, such as:

-* * * * * root /usr/sbin/dhcpsync host2

FILES

/etc/dhcpd.conf.shared default conf file that is to be

synced
/root/.ssh/dhcp-share default file name of the ssh1

private key

AUTHORS

Peter Poeml <poeml@suse.de>

BUGS

If you feel that this script could be improved, please
submit a bug report!

Someone who has access to the private key and the master's
IP address can overwrite the configuration file, possibly
causing harm.

DISCLAIMER

dhcpsync is provided ``AS IS'' and any express or implied warranties, including, but not limited to, the implied
warranties of merchantability and fitness for a particular
purpose are disclaimed.

SEE ALSO

dhcpd(8), /usr/share/doc/packages/dhcp/*

2002-01-27 1.10 DHCPSYNC.8(1)