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Re: Check if my IP address has changed ?

From: David Breakey
Subject: Re: Check if my IP address has changed ?
Date: Tue, 12 Feb 2013 10:51:57 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130106 Thunderbird/17.0.2

Even if it's not possible to do this directly in Monit, you should be able to hook into the interface management scripts (I believe a post ifup hook should be able to check whether the IP address is what you expect, and take whatever corrective action is deemed suitable; how to do this is utterly dependent on your distro).

However, why are you needing to do this? If you're using a static IP, then this shouldn't be an issue to begin with, unless there's something wrong with your system's interface management scripts--and if you're using DHCP, then assigning a "static" IP is the responsibility of the DHCP server, not the client.
Enterprise-class routers support static leases, where the DHCP server compares the MAC address to a fixed list and, if found, assigns the IP address in the list, rather than the usual round-robin approach. Typically, these "fixed" addresses are outside the normal DHCP range. Very handy when you want the convenience of DHCP, with the utility of fixed addresses (I use DHCP almost exclusively at home, with a short lease time; if I need to change network infrastructure--DNS, NTP, etc--I just reconfigure the DHCP server and it will hand out the new information when the leases are renewed, while preserving fixed IP addresses).
I never configure network-critical servers this way; they are always statically configured, but I only have one critical server in each of the networks I am responsible for (small networks).
If you're using a home or home-office router, then you're generally out of luck (commercially, this is considered a "premium" feature), unless you replace the firmware with something like OpenWRT (as I've done). If you decide to do this, check carefully that OpenWRT is compatible with your router hardware first.

Or, run a standalone DHCP server that supports it; dnsmasq handles this quite nicely if I recall (same software that OpenWRT uses, I think).
On 02/11/2013 07:34 PM, Stephen Butler wrote:
Is it possible to get monit to check my ip address, and if its not what its supposed to be, get it to run a sh script that changes the ip address to what It should be ?


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