The most common reason for being unable to connect to a processor over Ethernet is incompatible IP addresses for the processor and the computer attempting to connect. Processors without a control subnet (DIN-AP4, RMC4, etc.) ship in DHCP mode and must be either connected to a network with a DHCP server so that they can be assigned an IP address or be manually configured to have a static IP address before they can be connected to via Ethernet. 

Processors with a Control Subnet (CP4N, ZUM-HUB4, etc.) have a built-in DHCP server on the control subnet port, and by default the processor will have an IP address of 172.22.0.1 and any connected devices will be automatically assigned unique IP addresses in the range 172.22.0.0/16

For networks with a DHCP server or when connecting to a processor's Control Subnet, the laptop network adapter should be set to "Obtain IP Address" automatically. Otherwise, the laptop must also be manually configured with a static IP address in the same subnet range as the processor. Every device on the network must have a unique IP address, and setting a static IP address on a network that has a DHCP server may also result in devices being unable to communicate with each other.

Subnet ranges are determined by the subnet mask. For example, a device with an address in the range 192.168.0.0/16 (subnet mask 255.255.0.0) will be able to see devices between 192.168.0.0 and 192.168.255.255, while a device with an address in the range 192.168.0.0/24 (subnet mask 255.255.255.0) will only be able to see devices between 192.168.0.0 and 192.168.0.255

If you are unable to connect to the processor, verify that it is visible either using Crestron's Device Discovery Tool in Toolbox or by trying to ping the processor from Command Prompt on your laptop. If the processor cannot be reached, then there may be network issues that must be resolved before you will be able to connect.

If authentication is enabled on the processor, another possible reason for a laptop or a device to be unable to connect to a processor is that the processor may have blocked the IP address of the laptop/device or may have blocked the user that the laptop/device is attempting to use to connect. This occurs when a device attempts to connect to a processor with invalid credentials too many times in a row (such as may happen if a device's IP table is configured before the CS authentication is set up, or if a laptop user connects using incorrect username/password)

• IP addresses are blocked for 24 hours by default, but you can attempt to circumvent this block by changing your IP address and trying again
• Users are blocked for 30 minutes by default, and it is only possible to circumvent this if another user has already been created, otherwise you must wait for the block to expire before connecting again

The below commands are useful if you are able to connect to the processor through some other means (specific commands may vary depending on the device):

• listblockedip and remblockedip commands can be used to view/unblock an IP address
• listlockeduser and remlockeduser commands can be used to view/unblock specific users
• setloginattempts and setlockouttime commands can be used to modify how many login attempts are allowed before blocking an IP address and how long an address will be blocked
• setuserloginattempts and setuserlockouttime commands are used to modify how many login attempts are allowed before blocking a user and how long that user will be blocked
• setlogoffidletime command can be used to modify how long you can be inactive before the processor automatically logs you out