Stop devices from changing IP Addresses

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michaelkenward wrote:

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captgadget wrote:

Some people say it is a myth, but you might find it useful to go into the settings of these devices and telling them to use a particular IP address and then reserve that address on the router.

 

For example, I find that this helps to manage an array of NAS boxes that I can then get at simply by pointing a browser at the appropriate IP address.

 

 

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Have found it very helpful with devices like NAS to go to the device and set an IP address. Make sure the IP address is outside of the DHCP address range to prevent conflicts. Unlike some commercial DHCP solutions the DHCP support in Netgear routers does not do a ping ahead before assigning an IP address. Ping ahead tells the DHCP service if the IP address is already in use or not. 

> Some people say it is a myth, but you might find it useful [...]

   It's not a myth, it's a mistake.  There's a proper way to manage
static addresses, and that's not it.  More likely, you would find it
confusing and troublesome.

   The advantage of using only dynamic addresses (DHCP) is that they're
all managed in one place, on the DHCP server (on the router).

   If you configure a device with a static address ("go into the
settings of these devices"), then that address should not be in the DHCP
address pool; otherwise the DHCP server might unwittingly grant it to
some other device.

   This address-reuse problem can best be avoided by shrinking the DHCP
address pool from its default of every available address (".2" - ".254")
to something smaller, like, say, ".2" - ".99"), and using the non-pool
addresses (".100" - ".254") for devices with static addresses.  (Pick
the boundary wherever you want to provide the desired balance between
pool and static addresses.)

   Alternatively, you _could_ prevent that address-reuse problem by
creating a reservation for that address, but that would be unwise,
because it forces you to store the same datum in two places, which
_must_ be kept consistent.

   Let's say that you use the address-reservation method to avoid the
address-reuse problem, and then you decide to change the address of a
device.  If you change only the address reservation, then you do _not_
change the actual (static) address of the device.  But you do remove the
address-reuse protection from its actual (static) address.

   Or, if you change only the actual (static) address of the device (by
reconfiguring the device), then you _do_ change its address, but you
also destroy the address-reuse protection which the old address
reservation now provides to only the old address, not the new one.

   Sure, you can reserve a dynamic address for a device which is
configured with a static address, and that does solve one potential
problem, but that way is confusing, and requires great care whenever a
change is made (to keep the two data consistent).  Managing static
addresses properly (using only non-pool addresses) is simpler and more
reliable.  And that's no myth.

> For example, I find that this helps to manage an array of NAS boxes that
> I can then get at simply by pointing a browser at the appropriate IP
> address.

   How does that depend on whether those devices use reserved dynamic or
static addresses?  Either way, the device address is fixed.  Or is that
a myth, too?