I faced an interesting problem. So, I have Cisco WS-C2960-48TT-L connected with HP Procurve 2626 and Aruba 2930F switches. when I type "show CDP neighbours" command on the cisco switch I see nothing, but on the other switches, I can see information about the cisco switch. So, I think that my cisco switch can send out CDP messages, but cannot receive. How can I solve this problem?

Aruba enter image description here

HP enter image description here

Cisco enter image description here

  • 2
    Please, never use images for text. Simply copy the text, then paste it into the question using the Preformatted-text option ({}).
    – Ron Maupin
    Jul 21 '19 at 21:13
  • 3
    CDP is a Cisco proprietary protocol. Cisco has historically required a license to transmit CDP, but generally ignored anyone's receive-only attempts at CDP. Other vendors have similar protocols and requirements. If you want cross-vendor support, use LLDP.
    – Ricky
    Jul 21 '19 at 22:47

Ricky Beam's comment is the answer.

The Cisco originates CDP (Cisco Discovery Protocol) because it is Cisco.

HP and Aruba do not originate Cisco Discovery Protocol because they are not Cisco. They probably originate LLDP (Link-Layer Discovery Protocol).

Because HP and Aruba want to be able to sell their products in a Cisco-dominated network industry, they apparently "snoop" the CDP frames and let you see them.

You may need to enable LLDP on your cisco:

config t
  LLDP run
copy run start

To see LLDP neighbors on your Cisco, use one of the following

show lldp
show lldp neighbors

These protocols use L2 multicast. You may get "weird" results if you don't enable one protocol on all devices. Specifically, the CDP or LLDP frames may flood through devices with CDP or LLDP off and be detected by multiple devices on the other side. Easiest way to avoid this in a multi-vendor environment is to enable LLDP on all devices and use "show LLDP" commands consistently.

  • Thank you, for your response. But I found that "LLDP is supported on Cat2960 since IOS 12.2(37)SE". My version is 12.2(35)SE5. So, i should upgrade. Jul 22 '19 at 6:01
  • Yes. I can’t even get code that old without calling a TAC. 12.2(44)SE5 was released in 2009 and that’s deferred ;-). Happy upgrading! Jul 22 '19 at 6:20
  • The HP 2626 is ancient as well (end of sale was 2009)...
    – Zac67
    Jul 22 '19 at 6:29

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