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# |
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# $Id: dhcping.pod,v 1.1 2002/01/27 01:57:15 mavetju Exp $ |
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# |
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=head1 NAME |
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B<dhcping> - send a DHCP request to DHCP server to see if it's up and running |
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=head1 SYNOPSIS |
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B<dhcping> |
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[B<-v>] [B<-q>] [B<-i>] [B<-r>] |
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B<-t> I<maxwait> |
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B<-c> I<client-IP-address> |
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B<-s> I<server-IP-address> |
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B<-h> I<client-hardware-address> |
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[B<-g> I<gateway-IP-address>] |
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=head1 DESCRIPTION |
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This command allows the system administrator to check if a remote |
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DHCP server is still functioning. |
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Options are: |
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=over |
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=item B<-v> |
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Verbose, print some information. |
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=item B<-i> |
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Use DHCPINFORM packets. |
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=item B<-r> |
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Use DHCPREQUEST packets (default behaviour). |
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=item B<-q> |
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Quiet, print nothing on the screen. |
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=item B<-t> I<maxwait> |
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Maximum time to wait for an answer from the server in seconds. |
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Default is 3 seconds. |
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=item B<-c> I<client-IP-address> |
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Request this IP address. Note that this is also the IP address the |
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answer will be sent to. |
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=item B<-s> I<server-IP-address> |
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Send the DHCP packet to this IP address. |
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=item B<-h> I<client-hardware-address> |
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Use this hardware-address in the DHCP request. It can be up to |
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sixteen octets seperated by colons (i.e. 01:02:03:04) |
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=item B<-g> I<gateway-IP-address> |
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Use this IP address for the gateway IP address in the DHCP packet. |
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This option is currently broken. |
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=back |
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=head1 RETURN VALUES |
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If everything goes okay, it returns 0. If there went something |
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wrong, it returns 1. |
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=head1 SETUP |
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This program should be installed setuid root or ran by root only. |
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See SECURITY for more information. |
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On your DHCP server, add these lines to the dhcpd.conf: |
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host <your monitoring host FQDN> { |
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hardware ethernet <your monitor host mac address>; |
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fixed-address <your monitoring host IP address>; |
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} |
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Then try it: |
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$ dhcping -c I<your monitoring host IP address> \ |
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-s I<your DHCP server IP address> \ |
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-h I<your monitor host mac address> |
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It will either respond with "no answer" or "Got answer from: I<your |
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DHCP server IP address>" |
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The DHCP server logfile will give: |
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S<DHCPREQUEST for 192.168.1.1 from 00:20:18:56:29:8f via ed0> |
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S<DHCPACK on 192.168.1.1 to 00:20:18:56:29:8f via ed0> |
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S<DHCPRELEASE of 192.168.1.1 from 00:20:18:56:29:8f via ed0 (found)> |
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Running in DHCPINFORM mode with B<-i>: |
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If you see "DHCPINFORM from 192.168.1.1 via xl0: not authoritative |
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for subnet 192.168.1.0", you should add the authoritative statement |
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to the subnet, See dhcpd.conf(5) for details. |
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When running in very verbose mode, B<dhcping> tries to dump all |
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data of the send and received DHCP packets. It will first dump the |
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packet in hex-format, then decodes the header and finally the |
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options. |
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=head1 HOW IT WORKS |
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The client either sends a DHCPREQUEST or DHCPINFORM packet to the |
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server and waits for an answer. Then, if a DHCPREQUEST was send, |
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it will send a DHCPRELEASE back to the server. |
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=head1 SECURITY |
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This program is installed setuid root as it requires the privileges |
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to bind itself to port 68 (bootpc). Root privileges are dropped as |
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soon as the program has bound itself to that port. |
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=head1 BUGS |
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Currently (this may, or may not, change in the future) the ISC DHCP |
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daemon does not write leases with a fixed IP address in the |
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dhcpd.leases file. |
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DHCPINFORM packets can only be used on subnets the server is authori- |
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tative for. If the monitoring script runs on a subnet the server |
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isn't authoritative for, it should use the DHCPREQUEST packets. I |
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also experienced some problems with ISC DHCPD v2 servers, but that |
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is also in the README of it. |
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The B<-V> option is still working, but shouldn't be used for |
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debugging of the packets. Better use dhcpdump(8) for that, which |
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is available on my website. I wanted to remove it, but decided only |
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to do it from the documentation, not from the code. Maybe I'll need |
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it one day for debugging. |
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=head1 AUTHOR |
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Edwin Groothuis, edwin@mavetju.org (http://www.mavetju.org) |
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=head1 SEE ALSO |
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dhcpd(8), dhclient(8), dhcpd.conf(5), dhcpdump(8) |
