CTS 049: The Language on Cisco APs – NDP

If Cisco APs could talk to each other they would use NDP, Neighbor Discovery Protocol. NDP is important to Cisco RRM. It feeds a lot of the algorithms within RRM.

The purpose of Cisco NDP is to allow APs to build a “map” of their locations in relation to each other. Every 180 seconds an AP will send a neighbor discovery packet over the air to a multicast address of 01:0B:85:00:00:00 from each channel.

NDP packets are sent at the highest transmit power and at the lowest data rate supported by the transmitting channel.

In terms of configuration, we are provided with three options:

  • Channel Scan Interval – default is 180 seconds
  • Neighbor Packet Frequency – default is 180 seconds
  • Neighbor Timeout Factor – default is a value of 5

You can find these options in the WLC GUI:

Wireless > 802.11a/n/ac or 802.11b/g/n > RRM > General

Debug commands used to verify NDP

(Cisco Controller)> show ap auto-rf 802.11a AP1
Nearby APs
AP 00:3a:7d:44:44:44 slot 1.................. -23 dBm on 36 20MHz (192.168.1.5) AP4
AP 58:bc:27:33:33:33 slot 1.................. -18 dBm on 100 20MHz (192.168.1.5) AP3
AP 58:bc:27:22:22:22 slot 1.................. -40 dBm on 44 20MHz (192.168.1.5) AP2

AP1#debug capwap rm measurements
CAPWAP RM Measurements display debugging is on
*Aug 23 18:17:46.016: CAPWAP_RM: Timer expiry
*Aug 23 18:17:46.016: CAPWAP_RM: Neighbor interval timer expired, slot 1, band 0
*Aug 23 18:17:46.016: CAPWAP_RM: Triggering neighbor request on ch index: 2
*Aug 23 18:17:46.016: CAPWAP_RM: Sending neighbor packet #2 on channel 44 with power 1 slot 1
*Aug 23 18:17:46.016: CAPWAP_RM: Scheduling next neighbor request on ch index: 3
*Aug 23 18:17:46.230: CAPWAP_RM: Notification for Request id: 4044, slot: 1, status 1
*Aug 23 18:17:46.230: CAPWAP_RM: Neighbor packet sent successfully on 44
*Aug 23 18:17:46.233: CAPWAP_RM: Notification for Request id: 4044, slot: 1, status 1
*Aug 23 18:17:46.233: CAPWAP_RM: Neighbor packet sent successfully on 44
*Aug 23 18:17:49.017: CAPWAP_RM: Timer expiry
*Aug 23 18:17:49.017: CAPWAP_RM: Neighbor interval timer expired, slot 1, band 0
*Aug 23 18:17:49.017: CAPWAP_RM: Triggering neighbor request on ch index: 3
*Aug 23 18:17:49.017: CAPWAP_RM: Sending neighbor packet #3 on channel 48 with power 1 slot 1
*Aug 23 18:17:49.017: CAPWAP_RM: Scheduling next neighbor request on ch index: 4
*Aug 23 18:17:49.159: CAPWAP_RM: Notification for Request id: 4048, slot: 1, status 1
*Aug 23 18:17:49.159: CAPWAP_RM: Neighbor packet sent successfully on 48
*Aug 23 18:17:49.162: CAPWAP_RM: Notification for Request id: 4048, slot: 1, status 1
*Aug 23 18:17:49.162: CAPWAP_RM: Neighbor packet sent successfully on 48

AP1#debug capwap rm neighbor

CAPWAP RM Neighbor display debugging is on

*Aug 23 18:31:33.529: LWAPP NEIGHBOR: Pak size 104 from 58bc.27xx.xxxx, interface - 1
*Aug 23 18:31:33.529: LWAPP NEIGHBOR:  Updating existing neighbor 58bc.27xx.xxxx(1), rssi -35 on channel: 161 with encryption: 0
*Aug 23 18:31:33.529: LWAPP NEIGHBOR: Configured Antennas: 2, PA_POWER: 17, TPO_CONTRIBUTION: 3, Total NDP Power: 20
*Aug 23 18:31:33.529: LWAPP NEIGHBOR:  Neighbor update 58bc.27xx.xxxx(avg -36), new rssi -35, channel 161
*Aug 23 18:31:33.529: LWAPP NEIGHBOR: NDP-TLV: Received ndp-tlv payload
*Aug 23 18:31:33.529: LWAPP NEIGHBOR: NDP: copy TLV data to neighbor
*Aug 23 18:31:33.529: LWAPP NEIGHBOR: NDP Rx: From 58bc.27xx.xxxx RSSI [raw:norm:avg]=[-35:-35:-36] [Neigh Srv Chan: Neigh Off Chan : NDP Pwr]=[161:157:20  dB] Rcv Ch Max Pwr [20  dB]
*Aug 23 18:31:33.532: LWAPP NEIGHBOR: Pak size 76 from 58bc.27xx.xxxx, interface - 1
*Aug 23 18:31:33.532: LWAPP NEIGHBOR:  Updating existing neighbor 58bc.27xx.xxxx(1), rssi -36 on channel: 161 with encryption: 0
*Aug 23 18:31:33.532: LWAPP NEIGHBOR: Configured Antennas: 2, PA_POWER: 17, TPO_CONTRIBUTION: 3, Total NDP Power: 20
*Aug 23 18:31:33.532: LWAPP NEIGHBOR:  Neighbor update 58bc.27xx.xxxx(avg -36), new rssi -36, channel 161
*Aug 23 18:31:33.532: LWAPP NEIGHBOR: NDP Rx: From 58bc.27xx.xxxx RSSI [raw:norm:avg]=[-36:-36:-36] [Neigh Srv Chan: Neigh Off Chan : NDP Pwr]=[161:157:20  dB] Rcv Ch Max Pwr [20  dB]

Links and Resources

Cisco NDP via Packet6

Why Validation Surveys Aren’t Enough via Transmit Failure (Jake Snyder)

Wi-Fi Stickers via Access Agility

How The NFL and Its Stadiums Became Leaders in Wi-Fi Monetizing Apps and Customer Experience via ZDNet

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About the Author
Rowell, CWNE #210, is a network engineer in Higher-Ed. He enjoys working with wireless networking technologies and loves to share and engage with the community. You can connect with him on Twitter, LinkedIn, and Facebook.

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