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Enables or disables CDP read-only operation on the switch.
(Default: Enabled)
Example:
To disable CDP read-only on the switch:
switch(config)# no cdp run
When CDP is disabled:
•
show cdp neighbors
displays an empty CDP Neighbors table
•
show cdp
displaysGlobal CDP informationEnable CDP [Yes]: No
Enabling or disabling CDP operation on individual ports
In the factory-default configuration, the switch has all ports enabled to receive CDP packets. Disabling CDP on a
port causes it to drop inbound CDP packets without recording their data in the CDP Neighbors table.
Syntax:
[no] cdp enable {< [e] port-list >}
Example:
To disable CDP on port A1:
switch(config)# no cdp enable a1
Configuring CDPv2 for voice transmission
Legacy Cisco VOIP phones only support manual configuration or using CDPv2 for voice VLAN auto-configuration.
LLDP-MED is not supported. CDPv2 exchanges information such as software version, device capabilities, and
voice VLAN information between directly connected devices such as a VOIP phone and a switch.
When the Cisco VOIP phone boots up (or sometimes periodically), it queries the switch and advertises
information about itself using CDPv2. The switch receives the VOIP VLAN Query TLV (type 0x0f) from the phone
and then immediately sends the voice VLAN ID in a reply packet to the phone using the VLAN Reply TLV (type
0x0e). The phone then begins tagging all packets with the advertised voice VLAN ID.
NOTE: A voice VLAN must be configured before the voice VLAN can be advertised. For example, to
configure VLAN 10 as a voice VLAN tagged for ports 1 through 10, enter these commands:
switch(config)# vlan 10
switch(vlan-10)# tagged 1-10
switch(vlan-10)# voice
switch(vlan-10)# exit
The switch CDP packet includes these TLVs:
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CDP Version: 2
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CDP TTL: 180 seconds
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Checksum
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Capabilities (type 0x04): 0x0008 (is a switch)
•
Native VLAN: The PVID of the port
Chapter 7 Configuring for Network Management Applications
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Troubleshooting
