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dhcprobe.8
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.\" ========================================================================
.\"
.IX Title "DHCPROBE 8"
.TH DHCPROBE 8 "April 7, 2012" "April 7, 2012" "General Commands Manual"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
dhcprobe \- send a DHCP request to DHCP server to check its configuration
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
\&\fBdhcprobe\fR
[\fB\-v\fR] [\fB\-q\fR] [\fB\-i\fR] [\fB\-r\fR]
\&\fB\-t\fR \fImaxwait\fR
\&\fB\-c\fR \fIclient-IP-address\fR
\&\fB\-s\fR \fIserver-IP-address\fR
\&\fB\-h\fR \fIclient-hardware-address\fR
[\fB\-g\fR \fIgateway-IP-address\fR]
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This command allows the system administrator to check if a remote
\&\s-1DHCP\s0 server is still functioning.
.PP
Options are:
.IP "\fB\-v\fR" 4
.IX Item "-v"
Verbose, print more information. Apply multiple times to see \s-1DHCP\s0 configuration details, connecting progress and the package in hex format.
.IP "\fB\-i\fR" 4
.IX Item "-i"
Use \s-1DHCPINFORM\s0 packets.
.IP "\fB\-r\fR" 4
.IX Item "-r"
Use \s-1DHCPREQUEST\s0 packets (default behaviour).
.IP "\fB\-q\fR" 4
.IX Item "-q"
Quiet, print nothing on the screen.
.IP "\fB\-t\fR \fImaxwait\fR" 4
.IX Item "-t maxwait"
Maximum time to wait for an answer from the server in seconds.
Default is 3 seconds.
.IP "\fB\-c\fR \fIclient-IP-address\fR" 4
.IX Item "-c client-IP-address"
Request this \s-1IP\s0 address. Note that this is also the \s-1IP\s0 address the
answer will be sent to.
.IP "\fB\-s\fR \fIserver-IP-address\fR" 4
.IX Item "-s server-IP-address"
Send the \s-1DHCP\s0 packet to this \s-1IP\s0 address.
.IP "\fB\-h\fR \fIclient-hardware-address\fR" 4
.IX Item "-h client-hardware-address"
Use this hardware-address in the \s-1DHCP\s0 request. It can be up to
sixteen octets seperated by colons (i.e. 01:02:03:04)
.IP "\fB\-g\fR \fIgateway-IP-address\fR" 4
.IX Item "-g gateway-IP-address"
Use this \s-1IP\s0 address for the gateway \s-1IP\s0 address in the \s-1DHCP\s0 packet.
This option is currently broken.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
If everything goes okay, it returns 0. If there went something
wrong, it returns 1.
.SH "SETUP"
.IX Header "SETUP"
This program should be installed setuid root or ran by root only.
See \s-1SECURITY\s0 for more information.
.PP
On your \s-1DHCP\s0 server, add these lines to the dhcpd.conf:
.PP
.Vb 4
\& host <your monitoring host FQDN> {
\& hardware ethernet <your monitor host mac address>;
\& fixed\-address <your monitoring host IP address>;
\& }
.Ve
.PP
Then try it:
.PP
$ dhcprobe \-c \fIyour monitoring host \s-1IP\s0 address\fR \e
\-s \fIyour \s-1DHCP\s0 server \s-1IP\s0 address\fR \e
\-h \fIyour monitor host mac address\fR
.PP
It will either respond with \*(L"no answer\*(R" or "Got answer from: \fIyour
\&\s-1DHCP\s0 server \s-1IP\s0 address\fR"
.PP
The \s-1DHCP\s0 server logfile will give:
\s-1DHCPREQUEST\s0\ for\ 192.168.1.1\ from\ 00:20:18:56:29:8f\ via\ ed0
\s-1DHCPACK\s0\ on\ 192.168.1.1\ to\ 00:20:18:56:29:8f\ via\ ed0
\s-1DHCPRELEASE\s0\ of\ 192.168.1.1\ from\ 00:20:18:56:29:8f\ via\ ed0\ (found)
.PP
Running in \s-1DHCPINFORM\s0 mode with \fB\-i\fR:
.PP
If you see \*(L"\s-1DHCPINFORM\s0 from 192.168.1.1 via xl0: not authoritative
for subnet 192.168.1.0\*(R", you should add the authoritative statement
to the subnet, See \fIdhcpd.conf\fR\|(5) for details.
.PP
When running in very verbose mode, \fBdhcprobe\fR tries to dump all
data of the send and received \s-1DHCP\s0 packets. It will first dump the
packet in hex-format, then decodes the header and finally the
options.
.SH "HOW IT WORKS"
.IX Header "HOW IT WORKS"
The client either sends a \s-1DHCPREQUEST\s0 or \s-1DHCPINFORM\s0 packet to the
server and waits for an answer. Then, if a \s-1DHCPREQUEST\s0 was send,
it will send a \s-1DHCPRELEASE\s0 back to the server.
.SH "SECURITY"
.IX Header "SECURITY"
This program is installed setuid root as it requires the privileges
to bind itself to port 68 (bootpc). Root privileges are dropped as
soon as the program has bound itself to that port.
.SH "BUGS"
.IX Header "BUGS"
Currently (this may, or may not, change in the future) the \s-1ISC DHCP\s0
daemon does not write leases with a fixed \s-1IP\s0 address in the
dhcpd.leases file.
.PP
\&\s-1DHCPINFORM\s0 packets can only be used on subnets the server is authori\-
tative for. If the monitoring script runs on a subnet the server
isn't authoritative for, it should use the \s-1DHCPREQUEST\s0 packets. I
also experienced some problems with \s-1ISC DHCPD\s0 v2 servers, but that
is also in the \s-1README\s0 of it.
.PP
The \fB\-V\fR option is still working, but shouldn't be used for
debugging of the packets. Better use \fIdhcpdump\fR\|(8) for that, which
is available on my website. I wanted to remove it, but decided only
to do it from the documentation, not from the code. Maybe I'll need
it one day for debugging.
.SH "AUTHOR"
.IX Header "AUTHOR"
Edwin Groothuis, [email protected] (http://www.mavetju.org)
Johannes Buchner, [email protected] (https://github.com/JohannesBuchner/DHCProbe)
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIdhcpd\fR\|(8), \fIdhclient\fR\|(8), \fIdhcpd.conf\fR\|(5), \fIdhcpdump\fR\|(8)