Wireless AP Discovery

Wireless APs discover the IP address of a controller using a sequence of mechanisms that allow for the possible services available on the enterprise network. The discovery process is successful when the AP successfully locates a controller to which it can register.

Ensure that the appropriate services on your enterprise network are prepared to support the discovery process. The following steps are used to find a known controller:

1. Use the predefined static IP addresses for the controllers on the network (if configured).

   You can specify a list of static IP addresses of the controllers on your network. On the Static Configuration tab, add the addresses to the Wireless Controller Search List.

   

   Caution

   Wireless APs configured with a static Wireless Controller Search List can connect only to controllers in the list. Improperly configured APs cannot connect to a non-existent controller address, and therefore cannot receive a corrected configuration.
2. Use the IP address of the controller to which the AP last connected successfully.

   Once an AP has successfully registered with a controller, it recalls that controller's IP address, and uses that address on subsequent reboots. The AP bypasses discovery and goes straight to registration.

   If a known controller cannot be located, the following discovery process steps should be followed:

3. Use DHCP (Dynamic Host Configuration Protocol) Option 60 to query the DHCP server for available controllers. The DHCP server responds to the AP with Option 43, which lists the available controllers.

   For the DHCP server to respond to an Option 60 request from an AP, configure the DHCP server with the vendor class identifier (VCI) for each AP. Also, configure the DHCP server with the IP addresses of the controllers. For more information, refer to the Getting Started Guide.

4. Use a Domain Name Server (DNS) lookup for the host name Controller.domain-name.

   The AP tries the DNS server if it is configured in parallel with SLP unicast and SLP multicast.

   If you use this method for discovery, place an A record in the DNS server for Controller.<domain-name>. The <domain-name> is optional, but if used, ensure it is listed with the DHCP server.

5. Use a multicast SLP request to find SLP SAs

   The AP sends a multicast SLP request, looking for any SLP Service Agents providing the Extreme Networks service.

   The AP tries SLP multicast in parallel with other discovery methods.

6. Use DHCP Option 78 to locate a Service Location Protocol (SLP) Directory Agent (DA), followed by a unicast SLP request to the Directory Agent.

   To use the DHCP and unicast SLP discovery method, ensure that the DHCP server on your network supports Option 78 (DHCP for SLP RFC2610). The APs use this method to discover the controller.

   This solution takes advantage of two services that are present on most networks:

   • DHCP — The standard is a means of providing IP addresses dynamically to devices on a network.
   • SLP — A means of allowing client applications to discover network services without knowing their location beforehand. Devices advertise their services using a Service Agent (SA). In larger installations, a Directory Agent (DA) collects information from SAs and creates a central repository (SLP RFC2608).

     The controller contains an SLP SA that, when started, queries the DHCP server for Option 78 and if found, registers itself with the DA as service type Extreme Networks. The controller contains a DA (SLPD).

     The AP queries DHCP servers for Option 78 to locate any DAs. The SLP User Agent for the AP then queries the DAs for a list of Extreme Networks SAs.

     Option 78 must be set for the subnets connected to the ports of the controller and the subnets connected to the APs. These subnets must contain an identical list of DA IP addresses.