The show ip interface brief command provides a concise summary of the status and IP addressing configuration of interfaces on a Cisco router or switch. Here's what it displays:
Interface: The name of the interface (e.g., FastEthernet0/0, GigabitEthernet1/1).
IP Address: The Layer 3 IP address assigned to the interface (if any).
OK? Indicates the IP layer status of the interface (YES if operational, NO if not).
Method: How the IP address was configured (manual or DHCP).
Status: The Layer 1 status of the interface (up or down).
Protocol: The Layer 2 status of the interface (up or down).
Why other options are incorrect:
Layer 2 address: The show ip interface brief command does not directly display Layer 2 (MAC) addresses. You can use the show interface <interface-name> command for that.
Keepalive: Keepalives are used in some routing protocols but are not generally reflected in the output of the show ip interface brief command.
Encapsulation type: Encapsulation information is also not typically included in the show ip interface brief output.
Reference:
Cisco IOS show ip interface brief command: [invalid URL removed]
Example output of show ip interface brief: https://www.cisco.com/E-Learning/bulk/public/tac/cim/cib/using_cisco_ios_software/cmdrefs/show_ip_interface.