Deploying and Troubleshooting Cisco Wireless LAN Controllers

CAPWAP Session Establishment/AP Joining Process (Cisco Wireless LAN Controllers) Part 1

As mentioned earlier, the CAPWAP session is similar to LWAPP. The main difference is the use of DTLS for authentication (DTLS-handshake) and tunnel encryption (DTLS-application data). The following is an overview of the session establishment process: Step 1. Discovery request (optional) Step 2. Discovery response Step 3. DTLS session establishment; all messages below will be […]

CAPWAP Session Establishment/AP Joining Process (Cisco Wireless LAN Controllers) Part 2

DTLS Session Establishment The DTLS protocol is based on the TLS protocol. TLS is the most widely deployed protocol for securing network traffic. It defines four record protocols: ■ The handshake protocol: Used to negotiate security parameters and authenticate ■ The change cipher spec protocol: Triggers to enable the encryption that has been negotiated by […]

CAPWAP Session Establishment/AP Joining Process (Cisco Wireless LAN Controllers) Part 3

Join/Config/Run After the successful DTLS session establishment, the join and configuration requests/responses follow. Because after every ChangeCipherSpec in DTLS the session uses previous negotiated encryption, you only see "DTLS application data" in a sniffer trace, which makes all the following packets such as Join or Configure packets invisible. Also, refer to Figure 4-6, which shows […]

CAPWAP Session Establishment/AP Joining Process (Cisco Wireless LAN Controllers) Part 4

Troubleshooting CAPWAP Session Establishment/AP Discovery and Join Usually, in failures in which the DTLS is never established, you have to identify at what step the process is failing. Once again, you usually have to defer to a packet trace to determine that. You have to look at two different views: ■ At the WLC port […]

CAPWAP Communication: Control and Data Encryption (Cisco Wireless LAN Controllers)

After the DTLS session is established, CAPWAP control traffic is encrypted and CAPWAP data traffic can be encrypted. For troubleshooting reasons, it is possible to disable CAPWAP control traffic. Whether the CAPWAP control traffic is encrypted or not is controlled via the CAPWAP preamble. The CAPWAP preamble is common to all CAPWAP transport headers and […]

CAPWAP Communication: Sequence Numbers and Retransmissions (Cisco Wireless LAN Controllers)

The CAPWAP protocol operates as a reliable transport. For each request message, a response message is defined, which acknowledges receipt of the request message. In addition, the control header Sequence Number field is used, which is an identifier value used to match request and response packets. When a CAPWAP packet with a Request Message Type […]

CAPWAP Fragmentation and Path MTU Discovery (Cisco Wireless LAN Controllers)

Taking into account that CAPWAP is "tunneling" IP data traffic from wireless clients and that CAPWAP runs over WAN links (Hybrid Remote Edge Access Point [H-REAP] setups), it is important for troubleshooting to understand the fragmentation behavior as well as the Path MTU Discovery mechanism from CAPWAP. The following sections provide an overview of how […]

802.11 Bindings and Payloads (Cisco Wireless LAN Controllers)

As you learned at the beginning of this topic, the CAPWAP protocol does not include specific wireless technologies; instead, it relies on a binding specification to extend the technology to a particular wireless technology. Those binding specifications for the IEEE 802.11 wireless protocol are defined in RFC 5416. CAPWAP-Data Binding and Payloads To differentiate which […]

Controller Placement (Cisco Wireless LAN Controllers)

The Cisco Unified Wireless Network (CUWN) solution provides significant flexibility for network design and redundancy. Although the physical location of controllers and access points (APs) has some best practices depending on the actual network design, for the most part you can install a controller anywhere on your network and have the APs register to it […]

AP Placement (Cisco Wireless LAN Controllers)

The results of your wireless survey determine where to locate your APs on the campus, buildings, and floors. The survey tells you how many APs you need and what power levels provide the best coverage. Every wireless installation is unique, and what looks good to the human eye on a map might not be the […]