Capwap Study Notes-first knowledge of capwap (1)

2 first knowledge of capwap

2.1 Introduction to capwap

After talking about capwap for a long time, I haven't even said the full name yet, Khan ......

Capwap -- control and provisioning of wireless access points protocol specification. It consists of two parts: capwap protocol and wireless binding protocol.

The former is a common tunnel protocol that completes basic protocol functions such as AP discovery AC, and has nothing to do with the specific wireless access technology. The latter provides configuration management functions related to a wireless access technology. The former specifies what needs to be done at various stages, and the latter specifies how to accomplish these tasks in various access methods.

The capwap protocol was released in rfc5415 in April 2009. Currently, only RFC 802.11 is available for wireless bingding. It was also released in April 2009, with the RFC No. 5416.

PS: Let's take a look at the difference between wireless access methods such as 802.11, 802.15, 802.16, and 802.20.

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Currently, there are four types of wireless network protocols under IEEE802: 802.11, 802.15, 802.16, and 802.20. These four types of protocols also contain sub-protocols with different performance, it looks messy ......

The IEEE system defines the WLAN and Wireless Local Area Network (WLAN). It is designed for the LAN in the home and enterprise, the application scope is generally limited to a building or a small building group (such as a school or community ).

The definition of is actually a Wireless Personal Network (WPAN, Wireless Personal Area Network), which is mainly used for automatic interconnection between personal electronic devices and PCs, such devices include mobile phones, MP3 players, portable media players, digital cameras, and handheld computers.

802.16 is a broadband wireless access (BWA) technology used in long-distance and high-speed communication environments. It defines man and metropolitan area network ), performance comparable to Cable, DSL, T1 leased line and other traditional wired technology. 802.16 consists of two sub-protocols: 802.16 and 802.16a. The former has a working distance of 2 kilometers, and the transmission rate is between 30 Mbps and Mbps. The 802.16a transmission distance can reach 50 kilometers, the speed can also reach 75 Mbps-it can be seen that none of the above wireless communication technologies can overwrite 802.16a in terms of effective range and performance standards.

The characteristics of 802.16 and are similar, all of which have the characteristics of long transmission distance and fast speed. However, 802.20 is a mobile broadband access technology (mbwr) that focuses more on device mobility, for example, data communication can be achieved on high-speed trains and automobiles (802.16 cannot be achieved ).

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Capwap protocol features:

The AP automatically discovers the AC, the AC performs security authentication on the AP, the AP obtains the software image from the AC, and the AP obtains the initial and dynamic configuration from the AC. In addition, the system supports local data forwarding and centralized data forwarding.

The thin AP Architecture gives the AC a complete view of the entire WLAN Network, providing the foundation for the implementation of wireless roaming, wireless resource management, and other business functions.

2.2 terms

￠ Wireless controller (AC): The network entity that provides WTP-to-network access services at the data layer, control layer, and management layer of the network architecture.

￠ Capwap control channel: a bidirectional channel, which is defined by the ac ip address, wtp ip address, AC control port, WTP control port, and Transport Layer Protocol (UDP or UDP-lite, you can send and receive capwap control packets.

￠ Capwap data channel: a two-way channel defined by the IP address of the AC, the IP address of the WTP, the AC data port, the WTP data port, and the transport layer protocol (UDP or UDP-lite, you can send and receive capwap data packets.

Station station: a device with wireless interfaces

✓ Wireless terminal WTP: physical or network entity, including a RF antenna and the wireless physical layer that can transmit and receive data from the sta over the wireless access network.

2.3 capwap Mode

The capwap protocol supports two modes: Split Mac and local Mac.

Split Mac: in Split mac mode, all layer-2 wireless data and Management frames are encapsulated by the capwap protocol and then exchanged between the AC and WTP.

As shown in, wireless frames received from a station are directly encapsulated and forwarded to the AC.

Local Mac: The local forwarding mode allows data frames to be forwarded through a local bridge or tunnel in the form of 802.3 frames. In this case, the layer-2 wireless management frame is processed locally in the WTP and then forwarded to the AC.

The local forwarding mode is displayed. The wireless frames transmitted by the station are encapsulated into 802.3 data frames and then forwarded to the AC.

2.4 capwap load type

Capwap transport layer transport two types of load:

Producer data message

Encapsulate and forward wireless frames

Consumer Control Message

Manage messages exchanged between WTP and AC

Capwap data and control packets are sent based on different UDP ports and can be segmented. Therefore, data and control packets can exceed the MTU length.

2.5 capwap session creation process

The capwap protocol starts from the current stage. Wtps sends a discovery request message. Any AC that receives this request will respond to a discovery Response Message. When a response packet is received, WTP selects an AC to establish a secure session based on dtls. To establish a secure dtls connection, WTP requires a pre-supplied data, which will be described later. Capwap packets are segmented into the maximum length supported by the network.

Once the WTP and AC have established the dtls Session, the configuration is exchanged between the two to reach an agreement on the version information. During this switching process, WTP may receive the specified settings and then enable these settings.

When WTP and AC are switched between versions and settings, and WTP is enabled, capwap is used to encapsulate wireless data frames sent between AC and WTP. If the length of user data or protocol-controlled data exceeds the MTU between WTP and AC, The capwap protocol will shard L2 frames. The split capwap packet will be re-formed into the original encapsulation Packet