IP addresses on local network change

[Dave Ihnat]

On Mon, Oct 06, 2014 at 02:22:42PM +0200, Ralf Corsepius wrote:
> On 10/06/2014 01:02 PM, Angelo Moreschini wrote:
> That's not unusual with DHCP. DHCP assigned IP-addresses usually
> have limited life-time until they expire. After expiration machines
> may be assigned a new IP-address.

However, I will point out that DHCP servers _tend_ to reassign the same
IP address to a machine renewing its lease.  If you're seeing the address
change frequently, I would also wonder if there are dueling DHCP servers
on the segment.  Determine what should be the definitive DHCP server and
make sure nothing else thinks it is also a DHCP server (e.g., other
computers, a firewall/router appliance, etc.)

> If you want to access a machine under a static IP-address, you'd
> have to set up your DHCP-server accordingly. How to do so would
> depend upon you DHCP-server's implementation.

Well, actually, there are a couple of approaches:

  o A DHCP server should be configured to only use a portion of the
    available IP address range for the subnet.  For instance, if you're
	using a RFC1918 IPv4 subnet of 192.168.100.0/24, it would be common to
	restrict DHCP to the range 192.168.100.100-199.  Anything below or
	above that range is available for static assignment.

  o You can reserve IP addresses within the DHCP pool by MAC address.
    This is usually used when you've a legacy IP assignment that is in
	the DHCP pool and, for whatever reason, is difficult to change.

Cheers,
--
	Dave Ihnat
	dihnat at dminet.com