Configure via DHCP Option 43
Goal: deliver the ACS URL to devices using DHCP's Option 43, in topologies with DHCP dedicated to TR-069.
Providers using a topology with DHCP exclusive to TR-069 can send parameters via Option 43: besides providing the IP for the device to communicate at Layer 3, it tells the device which ACS server it should connect to.
How the DHCP exchange works
CPE
DHCP Server
ACS Server
1) DHCP Discover
2) DHCP Offer
3) DHCP Request (Option 55 += 43) (Option 60)
4) DHCP ACK + Option 43 (ACS Parameters)
5) CPE connects to the ACS server (CWMP)
CPE
DHCP Server
ACS Server
Warning: Option 43 is not standardized
Option 43 is defined in RFC 2132 as "Vendor Specific Information" — meaning each manufacturer may use a different format. That's why you need to know:
- Which device will be used.
- Whether it accepts receiving the ACS URL via Option 43.
- Which format it expects.
Multiple formats and Cpehub's Generator
Some servers support several Option 43 formats at once; others don't (Mikrotik, for example, doesn't accept multiple options with the same code). To help build the correct Option 43 value per manufacturer, Cpehub offers the DHCP Option 43 Generator (in Administration).