it depends.
My rules of thumb are:
- The PBX needs to be static on the Internet LAN. This can be allocated in DHCP or set in the interface, but everything needs to know where the server is, so it needs a static address.
- If the PBX is exposed to the Internet and there’s no intervening firewall, the PBX can get by with a DynDNS address if you are willing to put up your phones not connecting to the PSTN on a regular bases. This is not a “best practice” solution, but the system supports it.
- Infrastructure equipment (on the LAN) should always have static address, either set in the hardware or set as allocated address in DHCP. Both is also a good idea (use DHCP but set the :“backup” address to the static address you are using).
- Phones do not NEED static addresses, but I always allocate my phones as allocated addresses in DHCP. I use Chan-SCCP-B for my Cisco phones, so I have to set them up in DHCP anyway - it’s just one extra step to allocate them in the same group.
= Any item in your system that needs to be used for a service (a printer, for example) should always have a static address. DHCP pre-allocated address is fine here. With modern networking setups, you can get by with “more dynamic” addresses, but setting up a known address for a service bearing machine just makes sense. - Everything else can have dynamic addresses.
You can get by with a dynamic address for your WAN interface - the system can adjust to using dynamic addresses in the Integrated Firewall. If you can get a static WAN address, I highly recommend it - it makes setting up the system less “troublesome”.