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Knowledge Base

WLAN AC option 43 with DrayTek2860 as Gateway

Publication Date:  2019-07-14  |   Views:  3217  |   Downloads:  0  |   Author:  f84079177  |   Document ID:  EKB1000714061


Issue Description


Customer required interconnect CAPWAP beyond the subnet that the AC6605-26 is configured.
The customer have MPLS which many AP’s are connected to on many different subnets.

The AP can be configured manually to learn the AC controller IP address and go online but customer wants this to be made automatically.

They are using DrayTek 2860 routers at all the sites that they are using Huawei AP’s.

The customer ask how to configure option 43 in this situation for to AC, a primary and secondary.


Alarm Information


Handling Process

If an AP and the ACs are located in different network segments, the AP cannot discover the ACs through broadcast after it obtains an IP address from the DHCP server. To address this problem, configure Option 43 on the DHCP server to advertise AC IP addresses to the AP.

After Option 43 is configured, the AP unicasts Discovery Request packets to the IP addresses carried in Option 43. If the IP addresses specified by Option 43 do not respond, the AP broadcasts Discovery Request packets to request IP addresses of the ACs in the local network segment. Option 43 only needs to carry addresses of the active and standby ACs for the AP and does not carry irrelevant active ACs' IP addresses; otherwise, the AP may not connect to the correct AC.

Root Cause

The configuration into the DHCP server to configure Option 43 must be following the ASCII values in Hexadecimal format.





 Example configuration:

First AC capwap IP is;

Second AC capwap IP is;

2E = .

2c = ,

1.       convert
into ascii hex:

a.       First

b.      Second

2. the length of the ascii is 31 bytes (hex 1F)

3. Code ID is 03

4. Result: 031F3139322E3136382E3235342E3235332c3139322E3136382E3235332E323533