Zyxel and CAPWAP

By | August 29, 2014
NWA 3160n

A Zyxel NWA 3160-n Acces Point

Today I've got a Zyxel NWA 3160-n AP, and I turned it into managed mode to try to connect  it to my open source CAPWAP AC.

No luck so far ...

Concerning CAPWAP, Zyxel seems to be in no way better than Cisco. The Zyxel AP is (as almost expected) not really CAPWAP-conform, just  like a Cisco 1131AG.

Things I've found out so far using the newest firmware version 2.23(UJA.6)C0, downloaded here:

  • The message element length field, sent in the control header of a discovery request message, contains a value which is too small by three. The reason for this is obvious: Zyxel counts only the number of bytes of message elements, but not, as required in RCF 5415,the number of bytes following the sequence number in the control header, which would result in three more bytes.
  • The discovery request message contains no wtp board data message element and no wtp radio information. Both are required by RFC 5415.
  • The Num Encrypt field in the WTP descriptor message element is set to zero (as with  Cisco), followed by nothing (that's a little bit better than Cisco).

After answering to a received discovery request from the AP with a well-formed discovery response, the AP sends immediately a new discovery request message, ignoring the discovery response, not waiting for a potential other discovery responses, no sulking state ever.

I don't know, why the AP throws my discovery responses, generated by AC-Tube, away. I think, the AP wants acertain vendor specific payload, but I have still no evidence.

One thought on “Zyxel and CAPWAP

  1. Nobody of Import

    How conformant do you believe yourself to be to the RFC's requirements, barring, for a moment, trying to work with any of the commercial vendor devices claiming "CAPWAP"? (Bear with me...)


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