what is the significance of the output of this command ? Cisco CLI

Question

When i enter this command i get my neighbors with some IPs and these are not their Telnet IPs. Can you tell me where those IP belong to ?

sh cdp entry * protocol

I want to know what are those IPs?

Answer 1

According to the prefix name "RTR_" those devices are routers.

Routers generally have several IP addresses, so CDP may display only one of those IP addresses. (Well, even layer 2 switches can have several IP addresses.)

From this post by MAG03 on Experts-Exchange.com, which is consistent with what I see right now one some switches, it seems that:

CDP determines the IP address to use by first looking at the directly connected interface and seeing if there is an IP address on it. If there is, that IP address will be used. If the link is a trunk CDP will choose the lowest IP address of the vlan interfaces as the IP address it will use to describe the neighbor.

so if SW1 has vlans with IP 1.1.1.1 and another vlan with ip 2.2.2.2, SW2 has vlans with IP addresses of 3.3.3.3 and 4.4.4.4, and the link connecting the two is a trunk.

Given that CDP is enabled on the trunk interface SW1 will be shown as having an address of 1.1.1.1 and SW2 will have an addess of 3.3.3.3 in the show cdp neighbor detail output.

Usually the IP used to manage a device is the loopback IP and so is never directly connected to a CDP neighbor and is unlikely to be shown in your CDP command

However if you issue the show cdp neighbors detailcommand you will see this IP address.

Notes:

• the behavior may change depending on the IOS version, and is also different between IOS and NX-OS, probably for CAT-OS too.
• you mentioned telnet, which is totally insecure, you should disable telnet and use SSH instead.