NAME
ipchgmon.pm - Watches for changes to public facing IP addresses
SYNOPSIS
perl ipchgmon.pm --file c:\data\log.txt --server example.comWho knows? It might even work. More usually, in a cron job:
perl ipchgmon --file ~/log.txt \
--server back_office_top_shelf \
--dnsname example.com \
--leeway 86400 \
--email serverchange@example.com \
--mailserver 192.168.0.2 \
--mailfrom ipchgmon@example.com \
--mailsubject 'Change of IP address'BACKGROUND
I and friends run email and other servers at home. I pay for a static IP address with the clause in my contract that force majeur may require a change. Others are on dynamic addresses. Should the public facing address change, we want to know. This modulino is intended to monitor the public IP address and shout for help should the address change. One friend is looking at code to change public DNS records automatically.
DESCRIPTION
This modulino is intended to be run automatically as a cron job. It should check whether the server running it has changed its IP address. If so, messages should be sent to those specified.
Either IPv4 or IPv6 or both formats can be tested. It might well be that different servers handle the different types.
There are three issues that may be checked. The first is connectivity. If there is no connectivity, messages should be sent. No further issues will be tested.
The second issue that will be tested is whether the IP address has changed. The current public-facing IP address is established via internet use and compared to a log file, specified by the "--file" option. If it is not the last entry in the log, messages will be sent.
Finally and optionally, the DNS name of the server will be used to get another IP address from global DNS. If this is not the last address in the log file, messages will be send unless a leeway has been specified and this has not expired.
If connectivity is lost, the number of retries and the wait will both be options in a later version. At present, or if the retries all fail, someone should be sent a message.
The design includes three forms of message, SMS, HTTP and email. It is reasonable to send an email if internet connectivity is lost; the server may be internal. SMS may be harder to justify. HTTP must depend on the location of the server.
There is currently no facility to send different classes of message to different addresses. There is nothing inherently impossible about writing code to do this if it proves desirable.
If the IP address has changed, messages should be sent without delay or retries.
ON ARGUMENTS AND OPTIONS
These are processed by Getopt::Long. This means that shorter versions may be used. If the first letter of an argument or option is unique, the call may be reduced to a single minus sign and the first letter. So the "email" argument has an alias, "mailto". But the alias must be specified as "--mailt" at least, while "email" can be reduced to "-e".
ARGUMENTS
--file filename THIS OPTION IS COMPULSORY unless --debug is used.
The file "filename" will be created if it does not exist.
It may be preferable to use a fully qualified filename.
Attempting to write to a non-existent directory or without
the necessary permissions will cause an error. The file is
plain text containing the IPv4 and IPv6 addresses of the server.
--server name THIS OPTION IS COMPULSORY unless --debug is used.
It is the name that will be used to identify the machine
should internet connectivity be lost or the IP address
change. It is not used internally and should not be
confused with the dnsname.
--dnsname name The name of the server in global DNS.
--leeway time This option specifies how many seconds should elapse from
an IP address changing on DNS to a second email being sent.
It is used only in conjunction with dnsname. If dnsname
is unspecified, the value of this option is meaningless.
It isn't compulsory, but without it, messages will be sent
every time the modulino finds the IP address is not the
same as returned by DNS. This is fine if you like getting
up every hour during the night. Otherwise, use something
like 86400 (one day).
--email address Multiple instances of this option are acceptable. An email
will be sent to each, if possible.
--mailto Synonym for --email.
--mailserver Must be followed by the name or ip address of the outbound
server. Some systems may have a default for this.
--mailport Must be numeric. Will default to 25 if omitted.
--mailfrom Most servers will insist on this, but some systems may
have a default.
--mailsubject Can be omitted if desired. A default would be created
which would be different for each message type. Subjects
that include spaces would need quoting. The quote character
can be OS dependent.OPTIONS
--help Brief manual
--man Full manual
--versions Code info
--debug Debugging information
--singleemail Sends one email at a time. Prevents multiple email
addresses appearing in each email and prevents server
confusion if different mechanisms are used for different
destinations. Yes, it can happen.
--4 Check IPv4 addresses. Both will be checked if neither
or both options are used.
--6 Check IPv6 addresses. Both will be checked if neither
or both options are used.TO DO
* Implement SMS messages
* Implement HTTP messages
* implement config file
COPYRIGHT AND LICENSE
Copyright (C) 2022 by John Davies
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
CREDITS
https://www.perlmonks.org/?node_id=155288 for the getopt/usage model.
Fergus McMenemie for the talk on modulinos (https://www.youtube.com/watch?v=wCW4tpMgdHs).