best practice for fixed-address / reserved leases

[Bill Shirley]

Fixed addresses should NOT be in any range.  It's possible for DHCP to assign that address
before the device with that fixed address gets it.

BTW, your subnet and addresses are not in the RFC 1918 range. https://tools.ietf.org/html/rfc1918

The Internet Assigned Numbers Authority (IANA) has reserved the
    following three blocks of the IP address space for private internets:

      10.0.0.0        -   10.255.255.255  (10/8 prefix)
      172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
      192.168.0.0     -   192.168.255.255 (192.168/16 prefix)

You are using public addresses on your private network.

Bill

On 12/30/2020 7:57 AM, Michael Schnyder wrote:
> Hi
>
> Need to have an answer for correct configuring / assigning fixed ip addresses:
>
> We defined a while ago our "best practice" to configure a fixed address definition outside the dhcp range:
>
> -------------- example
> subnet 172.1.2.0 netmask 255.255.255.0 {
>    range 172.1.2.10 172.1.2.50;
>    option routers 172.1.1.1;
>    default-lease-time 21600;
> }
> # Fixed Address 1
> host abc {
>    hardware ethernet ab:c2:33:22:66:44;
>    fixed-address 172.1.2.51;    ### <- ip is NOT within the range 172.1.2.10 172.1.2.50;
> }
> # Phone Fixed Address
> host cde {
>    hardware ethernet cd:e2:33:22:66:44;
>    fixed-address 172.1.2.52;    ### <- ip is NOT within the range 172.1.2.10 172.1.2.50;
> }
> ------------- example end
>
> For me it's unclear why we should define it like that and unfortunately, I could not find yet an answer in the manual (also see [1]), therefore my question:
>
> Is it mandatory that a "fixed" ip address is part of the range?
> Or is it mandatory that it is _explicitly not_ part of the defined range?
> Or does it matter at all? Can I define within the subnet whatever ip address I would like to?
>
>
> [1] https://kb.isc.org/docs/isc-dhcp-41-manual-pages-dhcpdconf#RESERVED%20LEASES
>
> Thanks for your tipps.
>
> Kind regards
> michael
>
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