Cisco discovery protocol Definition

[GustavWi]

Hi,

We at our company has to implement the CDP protocol on our devices connected to the switch. I have searched for the CDP protocol definition and the format of the TLVs but I have not found any. Where can I find the definition of this protocol?

[balaji.bandi]

have you looked this

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/15-mt/cdp-15-mt-book/nm-cdp-discover.pdf

BB

[GustavWi]

Yes,

It does not describe the TLV type id, length and the format of the value. This is what I am missing.

Thanks

Gustav Wiklander

[Diana Karolina Rojas]

Hello Gustav,

Maybe this can help you http://linux-ha.org/source-doc/assimilation/html/group__cdp__type__fields.html you have to know that for security reasons is not recomemded to use CDP, this is good for troubleshooting but in not secure, the best way is to have an updated diagram of your network in order to know how your devices are connected.

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Best regards,

[GustavWi]

Maybe this could help. I am specifically interested in the PoE part. I noticed for instance that the TVL for power available contains Request ID, Manager ID and power available. The TVL for power request I don't know.

[Diana Karolina Rojas]

Here are details for the POE TLV:

• Power TLV (Only applicable for PoE models)

 Request ID—(Only applicable for PoE models) Last power request ID received echoes the Request-ID field last received in a Power Requested TLV. It is 0 if no Power Requested TLV was received since the interface last transitioned to Up.

Power Management ID—(Only applicable for PoE models) Value incremented by 1 (or 2, to avoid 0) each time when the Available Power or Management Power Level fields change value. A Power Requested TLV is received with a Request-ID field which is different from the last-received set (or when the first value is received). The interface transitions to Down.

Available Power—(Only applicable for PoE models) Amount of power consumed by port.

Management Power Level—(Only applicable for PoE models) Display the supplier's request to the powered device for its Power Consumption TLV. The switch always displays “No Preference” in this field.

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Best Regards,

[GustavWi]

Ok,

Is there a document describing this?

[Diana Karolina Rojas]

Good morning!

Not a document but a Cisco publication, you can see it here https://www.cisco.com/assets/sol/sb/SG220_Emulators/SG220_Emulator_v1-0-0-18_20140626/help/Discovery17.html

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Best Regards,

[GustavWi]

Thanks,

That document describes the Power Available TLV but not the Power Requested TLV. The document also states that there exists such a TLV.

[Diana Karolina Rojas]

About the power Request I only found this information:

• These TLVs are supported only by the access point:

◦Power Consumption TLV: 0x0010—The maximum amount of power consumed by the access point. ◦Power Request TLV:0x0019—The amount of power to be transmitted by a powerable device in order to negotiate a suitable power level with the supplier of the network power.

for your reference: https://www.cisco.com/en/US/docs/wireless/controller/7.4/configuration/guides/system_management/config_system_management_chapter_010001.pdf

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Best Regards,

[GustavWi]

Thanks!
I am interested in switches and I believe they support TVL 0x0010 and TLV 0x0019 if they are PoE switch with CDPv2 protocol. Can you find the definitions for these two TLV's?

Regards Gustav

[Diana Karolina Rojas]

What kind of devices will you connect to the switches?

Best Regards,

[GustavWi]

We develop and manufacture network Cameras. Our customers often uses cisco switches with PoE. They want us to negotiate PoE via CDP instead of only lldp. So we have to implement it.