CDP negotiation of WLC/AP
The TLV list can filter the values contained in the CDP packet. What makes me curious is what is the condition for the successful CDP negotiation of the WLC or AP. The required fields that can be seen on the Cisco official website are Device-ID TLV and Address TLV.
The Address TLV and Device ID TLV are mandatory TLVs and they cannot be blocked.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/15-mt/cdp-15-mt-book/nm-cdp-secure-cdp.html
WLC
The CDP detail when the TLV list is not configured on the switch side is as follows.
(Cisco Controller) >show cdp neighbors detail Device ID: Switch Entry address(es): IP address: 100.106.32.132 Platform: cisco WS-C3750X-24P, Capabilities: Router Switch IGMP Interface: TenGigabitEthernet0/0/1, Port ID (outgoing port): TenGigabitEthernet1/1/1 Holdtime : 166 sec Version : Cisco IOS Software, C3750E Software (C3750E-UNIVERSALK9-M), Version 15.0(2)SE2, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2013 by Cisco Systems, Inc. Compiled Tue 05-Feb-13 11:45 by prod_rel_team Advertisement version: 2 Duplex: Full
When I configured the TLV list and filtered all the fields , the CDP negotiation obviously failed.
(Cisco Controller) >show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater,
M - Remotely Managed Device
Device ID Local Intrfce Holdtme Capability Platform Port ID
(Cisco Controller) >After many attempts, I found that Address TLV is the key to the success of CDP negotiations. The CDP detail at this time is as follows.
(Cisco Controller) >show cdp neighbors detail
Device ID: Switch
Entry address(es):
IP address: 100.106.32.132
Platform: , Capabilities:
Interface: TenGigabitEthernet0/0/1, Port ID (outgoing port):
Holdtime : 147 sec
Version :
Advertisement version: 2
Duplex: Unknown
(Cisco Controller) >show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater,
M - Remotely Managed Device
Device ID Local Intrfce Holdtme Capability Platform Port ID
Switch Ten 0/0/1 163 AP
After all TLVs are filtered on the switch side, the AP’s CDP is as follows. Although there is CDP neighbors, but the POE negotiation has failed.
AP#show cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone, D - remote_managed_device
V - CVTA, U - Unknown
Device ID Local Intf Hold-time Capability Platform Port ID
Switch wired0 178
Switch wired1 83
AP#show cdp inline_power
Power_Requested(mW) Power_Available(mW) Power_request-ID Power_management-ID
Not-negotiated Not-negotiated After that, I tried again and again. When I no longer filtered power -available, the POE negotiation succeeded.
AP#[*07/22/2018 00:06:01.7928] Waiting for uplink IPv4 configuration
show cdp inline_power
Power_Requested(mW) Power_Available(mW) Power_request-ID Power_management-ID
30000 30000 11292 27We can see in the official documentation that power -available contains the following four fields.
Specifies the information transmitted by all switch interfaces. This information permits a device that needs power to negotiate and select an appropriate power setting. The Power Available TLV includes four fields:
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/xe-3e/cdp-xe-3e-book/cdp-xe-3e-book_chapter_01.html
Request-ID field
Available-Power field
Power-Management-ID field
Management-Power-Level field
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/15-e/cdp-15-e-book.html
Summary
WLC
- Device-ID
- Address
AP
- Device-ID
- Request-ID
- Available-Power
- Power-Management-ID
- Management-Power-Level
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