DHCP Option 43 for ACS auto-configuration
Today we’re going to explore the famous DHCP Option 43, used mainly to autoconfigure devices such as Access Points, Switches, IP Phones, CPEs, IoT devices and others through TR-069. We will also show a configuration example using the DHCP Server of a Mikrotik router, delivering parameters via DHCP Option43 and allowing autoconfiguration of services in the process of assigning IP addresses to the device. This allows us, for example, to signal a controller external to the device automatically, even if the device has gone through a factory-reset. RFC 2132 “DHCP Options and BOOTP Vendor Extensions” [1] deals with various types of information that can be sent via the DHCP protocol, such as DNS, subnet mask, router address, vendor-specific attributes and much more. Option 43 is defined in this RFC as “Vendor Specific Information” and is used by DHCP clients and servers to exchange specific information with each other. The RFC does not specify what values I can send, nor what this information is, much less the data type. It merely describes the structure, which should be: Code Len Vendor specific information 43 n i1 i2 … Code 1 Len 1 Date 1 Code 2 Len 2 Date 2 Code n Len n Date no. T1 n1 d1 T2 n2 T2 … … … With this structure, each manufacturer or organization can model the data as is most convenient for their use. For example, for access-points the IP addresses of Wifi controllers can be configured, allowing them to be “joined” to the centralized controller, for IP Phones the IP or URL of the telephony server can be delivered and for routers that support TR-069 the ACS URL can be configured. And all this automatically! The focus of this article will be to show how to use option 43 together with TR-069, sending the URL from the ACS server to the CPE via the DHCP server. This allows the router, even when reset and without a configuration template, to learn the URL of the ACS server via DHCP, along with the user and password, the data needed to integrate with the ACS and allow the TR-069 to apply configurations to the CPE automatically. But before I continue, I’ll leave you with some links to other examples of option 43 use cases. Configure DHCP OPTION 43 for Lightweight Access Points: https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/97066-dhcp-option-43-00.html VLAN ID Discovery over DHCP: https://wiki.unify.com/wiki/VLAN_ID_Discovery_over_DHCP Use DHCP Option 43 for Unifi Access Point Provisioning:https://niksec.com/use-dhcp-option-43-for-unifi-accesspoint-provisioning/ How DHCP ended up in the TR-069 If you don’t know what ACS is, check out our other article . DHCP was introduced as one of the methods for ACS onboarding. Onboarding is the process by which the CPE/router is configured with an ACS server.There are three ways to onboard CPEs to an ACS server, according to the Broadband Forum’s TR-069 specification [2]: The ultimate goal of any of the three is one: to have the ACS server URL configured in the CPE so that it can be managed via the TR-069 protocol. DHCP Option 43 request process The BroadBand Forum defines some steps so that the CPE can get the ACS URL via DHCP. The picture below shows the steps, and we’ll talk about each of them in a moment. Communication step by step: The TR-069 specification also defines other fields/protocols that can be used for the same purpose: DHCPv4 Option 125, DHCPv6 Option 17. They also mention various post-reset discovery rules and how to deal with connectivity problems with the ACS. But they are beyond the scope of this article. Example of a DHCP transaction with Option 43 – Packet captures Mikrotik configuration example Here, we’ll see how to configure a Mikrotik router to deliver autoconfiguration parameters to “clients” via DHCP-Server using Option43. The configuration will be based on the topology below, similar to the one used in our tests with a Nokia CPE. First you need to have the DHCP Server configured, then link the DHCP Option43 settings. We used the network 192.168.2.0/24 and Vlan 881, as in our example: You might be wondering, where did the value of option 43 come from? There is a rule to be created, and you can see how to generate it for your ACS server in the following article. Conclusion In this article, we look at how to use DHCP’s “Option43” attribute to autoconfigure an ACS server on CPEs and various devices. We discuss how it works and how it can be used to automate the delivery of specific configurations to devices using a protocol as common as DHCP. Understanding the capabilities, features, and options supported by the manufacturer and equipment model helps us automate various configurations, including, but not limited to, managing a Nokia CPE via TR-069. References:[1] RFC 2132, DHCP Options and BOOTP Vendor Extensions, https://www.ietf.org/rfc/rfc2132.txt [2] TR-069, CPE WAN Management Protocol, https://www.broadband-forum.org/pdfs/tr-069-1-6-1.pdf
Netflow Configuration on Mikrotik RouterOS Routers
Netflow Configuration on Mikrotik Routers
