[C9800CL][#3]-AP Join Process

안녕하세요.

 

오늘은 AP가 WLC에 등록할때 AP입장에서 패킷이 어떻게 진행되는지 알아보겠습니다.

 

시스코 공식 홈페이지에 나와 있는지 문서 입니다.

https://www.cisco.com/c/en/us/support/docs/wireless/catalyst-9120axe-access-point/221056-understand-the-ap-join-process-with-the.html

Understand the AP Join Process with the Catalyst 9800 WLC

 

만약에 WLC에 다른 지역에 있는 상황이라면
Note: As per RFC 5415, CAPWAP uses the UDP Ports 5246 (for CAPWAP Control) and 5247 (for CAPWAP Data).

위에 포트는 방화벽에서 허용 되어야 합니다.

 

Session Establishment Process.

1. Access Point sends a Discovery Request. See the WLC Discovery Methods section for more information on this
2. WLC sends a Discovery Response
3. DTLS session establishment. After this, all messages after this are encrypted and are shown as DTLS application data packets in any packet analysis tool.
4. Access Point sends a Join Request
5. WLC sends a Join Response
6. AP performs an image check. If it has the same image version as the WLC, then it proceeds with the next step. If it does not, then it downloads the image from the WLC and reboots to load the new image. In such case, it repeats the process from step 1.
7. Access Point sends a Configuration Status Request.
8. WLC sends a Configuration Status Response
9. Access Point goes to RUN State
10. During the RUN state, CAPWAP Tunnel Maintenance is pefrormed in two ways:
    1. Keepalives are exchanged to mantain the CAPWAP Data tunnel
    2. AP sends an Echo Request to the WLC, which has to be answered with its respective Echo Response. This is to mantain the CAPWAP Control tunnel.

 

Wireless LAN Controller Discovery Methods

There are several options to let the Access Points know of the existance of one WLC in the network:

• DHCP Option 43: This option provides the APs the IPv4 address of the WLC to join. This process is convenient for large deployments in which the APs and the WLC are in different sites.
• DNS Discovery: APs queries the domain name CISCO-CAPWAP-CONTROLLER.localdomain. You must configure your DNS server to resolve either the IPv4 or IPv6 address of the WLC tto join. This option is convenient for deployments in which the WLCs are stored in the same site as the APs.
• Layer 3 Broadcast: The APs automatically send a broadcast message to 255.255.255.255. Any WLC within the same subnet as the AP is expected to respond to this discovery request.
• Static configuration: You can use the capwap ap primary-base <wlc-hostname> <wlc-IP-address> command to configure a static entry for a WLC in the AP.
• Mobility Discovery: If the AP was previously joined to a WLC that was part of a mobility group, the AP also saves a record of the WLCs present in that mobility group.

 

저희는 위에 방식중에 2가지를 테스트 해보겠습니다.

 

1. Static Configuration - AP에서 IP주소랑 Default Gateway를 설정하고 수동으로 WLC IP주소를 입력해서 WLC에 AP를 등록하겠습니다.

 

2. DHCP option 43 - DHCP를 이용해서 AP에 IP주소랑 Default Gateway를 할당하고 WLC주소도 같이 할당하여 AP를 WLC에 등록하겠습니다.

 

테스트는 다음 과정에서 진행 하겠습니다.