Hello everyone,
Today I will share with you the CAPWAP overview and tunnel establishment process.
1. CAPWAP Overview
Control and Provisioning of Wireless Access Points (CAPWAP) is defined in RFC 5415. A tunnel is established between an AC and an AP to carry control packets and user data packets, facilitating centralized management and protection of user data. The CAPWAP performs the following functions: automatic discovery of APs and ACs, operation and maintenance of their state machines, management of APs by the AC, service configuration delivery, and forwarding of STA data over the CAPWAP tunnel.
2. CAPWAP tunnel establishment
The CAPWAP tunnel establishment process is as follows:
The DTLS process and the Image Data process are not mandatory processes. During the DTLS process, encryption and decryption are implemented. During the Image Data process, version synchronization is required when the AP and AC versions are inconsistent.
Configure the AP to go online through Xstorm and collect the packets (excluding the DTLS and Image Data processes) during the CAPWAP tunnel establishment process. See the following figure：
2.1 DHCP Process
The AP requests the DHCP server to assign an IP address to itself.
2.2 Discovery Process
The AP discovers the AC that can be associated with the AP. The AP obtains the AC address through the DHCP ACK message in the DHCP process. Therefore, the AP sends unicast packets. The Request packet contains AP information.
After receiving the request packet from the AP, the AC returns a response packet carrying the AC information.
2.3 Join Process
The AP sends a join request packet carrying the AP version information, the fat, and fit mode.
After receiving the join request, the AC returns a join response, which also contains AC information.
2.4 Configure Process
The AP sends a Configuration Status Request message carrying AC name and radio information.
After receiving the configuration status request, the AC returns a configuration status response. No configuration is delivered in this phase.
2.5 Data Check Process
After the configuration process is complete, the AP starts the data check phase. The AP sends a Change State Event Request message carrying information such as radio and result code.
The AC replies with change state event response after receiving a change state event request.
2.6 Run Process
After receiving the change state event response, the AP enters the run state, establishes a data tunnel, and delivers the data tunnel forwarding table. Sends Keep alive packets.
The AC replies with keep alive after receiving keep alive form AP.
During the RUN process, keepalive packets are transmitted through the data port and echo packets are transmitted through the control port. No information about the echo packets is found.
When the AP enters the Run state, the control and data channels between the AP and the AC are established successfully.
2.7 Configure Process (update)
Subsequently, the AP and AC exchange configuration update request and configuration update response messages for configuration upgrade.
That is all I want to share with you! Thank you!
