CISCO Cyberops Security Fundamentals Section 01: TCP/IP Protocol Suite (Q 11-20)

An IPv4 address has 32 bits. This means that it is made up of a sequence of 32 binary digits (0s and 1s). Each bit in the address represents a specific value and together they form a unique identifier for devices connected to a network. The 32-bit IPv4 address allows for a total of approximately 4.3 billion unique addresses, which is why the world is transitioning to IPv6 that has a much larger address space.

The maximum value that can be represented in any octet of an IP address or subnet mask is 255. In binary, an octet consists of 8 bits, and the highest value that can be represented with 8 bits is 11111111, which is equivalent to 255 in decimal notation. This value represents the maximum range of possible values for an octet in an IP address or subnet mask.

The IP address 127.0.0.1 is known as the loopback address and is used by a host to establish an IP connection to itself for testing purposes. It is often referred to as the localhost address and is commonly used in network diagnostics and troubleshooting. When a host sends a packet to the loopback address, it is immediately returned back to the host without being sent over the network. This allows the host to test network functionality without the need for an external network connection.

The address 172.16.1.10 belongs to the Class B address. In Classful IP addressing, Class B addresses have the first two octets reserved for the network portion, while the last two octets are used for host addressing. The range of Class B addresses is from 128.0.0.0 to 191.255.255.255, and they are commonly used for medium to large-sized networks.

The /26 prefix represents a subnet mask that has 26 bits set to 1 and the remaining bits set to 0. In binary, this would be 11111111.11111111.11111111.11000000, which is equivalent to the decimal subnet mask 255.255.255.192.

The subnet mask is the mechanism that identifies the separation point of network addressing and host addressing. It is a 32-bit value that is used to divide an IP address into network and host portions. The subnet mask determines which bits in the IP address represent the network address and which bits represent the host address. By comparing the IP address and the subnet mask, a device can determine whether a destination IP address is on the same network or a different network, allowing for proper routing of network traffic.

A Class B network has a subnet mask of 255.255.0.0, which means that it can have a maximum of 65,534 hosts. The first and last IP addresses in the range are reserved for network and broadcast addresses respectively, leaving 65,534 usable hosts.

The IP address 191.168.0.252 belongs to Class B of IP addresses. In Class B, the first two octets are used to identify the network, while the remaining two octets are used to identify the host. The range of Class B IP addresses is from 128.0.0.0 to 191.255.255.255, and they are typically assigned to medium-sized networks.

When a host fails to obtain an IP address via DHCP, it typically assigns itself an Automatic Private IP Address (APIPA) in the range of 169.254/16. This range is reserved for link-local addressing, meaning it is used for communication within a single network segment and is not routed across different networks. APIPA addresses are automatically generated by the host and are not managed by a DHCP server.

The class of an IP address is determined by the most significant bit (MSB) pattern. The MSB pattern indicates the range of IP addresses that belong to a particular class. The MSB pattern can be used to identify whether an IP address belongs to Class A, Class B, Class C, Class D, or Class E. Each class has a different range of IP addresses, and the MSB pattern helps in identifying the class to which an IP address belongs.