On 06/02/2021 22:00, Chris Green wrote:
Harry Bloomfield, Esq. wrote:
Chris Green has brought this to us :
Unless you re-use addresses that happens anyway with DHCP, I don't
think any system on my LAN has ever changed its IP and nearly all are
assigned by my DHCP server.

Switched off, items can time out from the DHCP server, unless you set
them up not to.

Yes, but when they reconnect they get the same IP back. E.g. I go
away for weeks at a time with my laptop but when I come back home it
always gets the same IP. This is how it's meant to work, the DHCP
server *does* remember MAC addresses and will give the same address to
the same device every time unless there's a very good reason for not
doing so.

If the DHCP server remains powered all the time, and only the client is
disconnected, then *most* routers will reassign the same IP. Generally
this is an "ok" thing on home networks, although it can be a limitation
where there are lots of guest devices that come and go, since you will
run out of DHCP pool addresses eventually, and the router will be forced
to reallocate IP addresses to new MAC addresses. So stuff works for a
fair while before something breaks without warning. (like someone's HP
wifi connected printer "vanishes" after many weeks of working just fine!)

If the router is powered off, then all bets are off, since it may have
no non volatile record of the IP to MAC parings.

If you want to have static addresses, but have them allocated via
DHCP[1], then you need to use the capabilities available in many routers
to permanently bind an IP to a MAC address, and then save that in the
routers non volatile configuration.

Lastly remember that not all SOHO routers are created equally - so do a
more reliable job of address allocation than others.

[1] this being the industry preferred way of allocating static IP
addresses on larger networks these days.

--
Cheers,

John.

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