I tested in Packet tracer and I don't see that CDP uses an IP address of another interface for the CDP neighbor, it just leaves it empty but still works as usual. I don't see how you guys say it is B, but the simulation on PT says otherwise. I'm going with C.
According to 4aynick who tested it through GNS3 and the CISCO documentation, answer B is correct, perhaps in Packet Tracer there is indeed this limitation, but it should include the ip address of another interface in an example of a #show cdp neighbors detail command, which does not happen leaving the ip address field empty (as I tested), but in GNS3 it manages to acquire the ip address of another interface (as mentioned by 4aynick), as well as also mentions the CISCO documentation, in this case, taking this into account limitation of Packet Tracer, I agree with answer B “updates the ip address of another interface”.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/15-mt/cdp-15-mt-book/nm-cdp-discover.html#:~:text=Restrictions%20for%20Using%20Cisco%20Discovery%20Protocol,-Cisco%20Discovery%20Protocol&text=Cisco%20Discovery%20Protocol%20is%20not,the%20non%2DIP%20address%20interface
B is correct. I just tried it in GNS3, and the "show cdp neighbors detail" command response included the ip address of another interface of the router.
unfortunately this is what happens, according to the cisco documentation (and GNS3 according to 4aynick), so we have to pay attention to the repeated IP addresses in the CDP "show" outputs.
Dude, I got confused with you here. You said Packet Tracer isn't reliable and therefore you disagree with his reasoning..... But then you agree with his answer. Lol wtf?
The Right answer is B. If a neighbor has no IP address on an interface enabled with Cisco Discovery Protocol, the IP address of another interface will be updated as IP address for the non-IP address interface.
Reference: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/cdp/configuration/15-mt/cdp-15-mt-book/nm-cdp-discover.html
What is the another interface? The C is correct. CDP does not need IPs to works normally
https://learningnetwork.cisco.com/s/question/0D53i00000Kt3Mp/how-does-cdp-work-without-l3-addresses
Read his link!
"If a neighbor has no IP address on an interface enabled with Cisco Discovery Protocol, the IP address of another interface will be updated as IP address for the non-IP address interface."
B is correct, as stated by Gere.
CDP (Cisco Discovery Protocol) operates normally without an IP address on the interface, but it cannot provide IP address information for that neighbor. It still shares other details like device ID and platform.
CDP (Cisco Discovery Protocol) operates normally without an IP address on the interface, but it cannot provide IP address information for that neighbor. It still shares other details like device ID and platform.
I would go with C because CDP does not provide information of another device connected to the neighbor only the information of the immediate neighbor and its direct cdp enabled interface.
In a CDP (Cisco Discovery Protocol) environment, when the CDP interface on an adjacent device is configured without an IP address, CDP operates normally, but it cannot provide IP address information for that neighbor.
CDP gathers and exchanges information about directly connected Cisco devices, such as the device ID, port ID, capabilities, platform, and IP address if it is configured. If an interface does not have an IP address, CDP will still function normally but will not be able to provide IP address information for that particular neighbor interface.
Given this understanding, Option C remains the correct answer: CDP operates normally, but it cannot provide IP address information for that neighbor.
It's possible that the source suggesting Option B is mixing up concepts. For example, another interface on the same device might have an IP address, but CDP would not use it to fill in the missing information for an interface that does not have an IP address.
Explanation:
CDP is a Layer 2 protocol, so it does not require an IP address to function.
If the adjacent device's interface does not have an IP address configured, CDP will still operate and provide information such as device ID, port ID, capabilities, and platform.
However, since there is no IP address configured on the interface, CDP will not be able to provide IP address information for that specific neighbor.
The other options are incorrect because:
A: CDP does not become inoperable; it continues to function at Layer 2.
B: CDP does not use the IP address of another interface; it simply cannot provide IP address information for the interface without an IP.
D: CDP can still provide other information (e.g., device ID, port ID) even if the IP address is missing. :::*Deepseek*
Guys, CDP is layer 2 protocol it does not need IP address to get the neighbour details. The correct option is C. You can also research on web or through Different AI.
ChatGPT voted C
Me:
"Won't it show the IP address of another interface of the device?"
ChatGPT:
"Yes, you're correct! If a device has multiple interfaces and one of those interfaces has an IP address configured, CDP will display the IP address of a different interface if it’s available."
CDP works on layer 2. It means there is no require for an IP address of the neighbor device to collect its information. The neigbors devices are directly connected, they can learn each other's MAC address.
CDP is a Layer 2 protocol, which means it operates independently of Layer 3 (IP) addresses. As a result, CDP can still exchange information such as device identifiers, port identifiers, capabilities, and platform information with neighboring devices, even if the interface does not have an IP address configured.
However, without an IP address on the interface, CDP cannot provide IP address information for that neighbor because there is no IP address to report. Despite this, other information can still be exchanged and displayed through CDP.
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