CDP broadcast questions in a standard AP

Let say I have radio 1 connected to radio 2 in wireless. Then the two radios send a CDP packet to each other. What will happen on a Access Point. Is there any standard for those APs in the markets?

Is the information on the CDP packet stored on the neighboring radios that we can query to discover the neighbors?

Look at this scenario.

[Cisco switch] ←Ethernet→ [AP #1] ⇠Wi-Fi⇢ [Client #2]

At the moment, the Cisco switch can see both AP #1 and #2 as neighbors but not sure if that is correct behavior? I would expect that the Cisco switch can only see AP #1 and you will need to query the cisco-cdp-mib in AP #1 to locate AP #2.

Appreaciate if anyone here can give me some hints.

Jess

Posted 2017-02-14T03:39:57.657

Reputation: 103

Two APs don't generally connect to each other, so even if "AP #2" was manufactured as an AP, it's acting like a client station here, I think. – user1686 – 2017-02-15T06:45:18.127

@grawity noted. – Jess – 2017-02-15T08:23:55.000

Answers

CDP packets look like regular multicast Ethernet frames, sent to the 01:00:0C:CC:CC:CC multicast address. (Remember that CDP is a proprietary protocol and its support is not required for Ethernet devices.) So it's quite normal that a CDP-unaware bridge simply forwards the announcements like it would do for any other multicast or broadcast frame.

In particular, if your AP runs regular Linux and implements CDP handling in a userspace daemon (like cdpd or lldpd), then that daemon can receive annoucements and send its own, but it cannot prevent the in-kernel bridge from forwarding received ones between bridge ports.

Note that the situation is different with LLDP, which uses multicast group addresses that are explicitly defined by IEEE 802.1Q-2014 (page 122) as non-forwardable, regardless of whether the bridge supports LLDP or not.

user1686

Posted 2017-02-14T03:39:57.657

Reputation: 283 655