M6: IPv4 Address Structure

CISCO Net Device: Calculate an IPv4 subnetting scheme to efficiently segment a network.

Subnet Mask

Is what tells every device where the split between network and host portion of an IPv4 address (32 bit number). It determines routing, addressing, and how devices communicate.

Network portion

Identifies the network

Host Portion

Identifies a device within a network.

CIDR Notation

Critical for Modern Networking. It expresses the subnet mask as /number of network bits.

• /24 → 255.255.255.0

• /16 → 255.255.0.0

• /8 → 255.0.0.0

ANDing

It is a bit-by-bit comparison. When a device receives an IPv4 address and subnet mask, it performs this process. Result = network address. It is a mathematical operation that extracts the network portion from IP address. It leaves the host portion behind.

Prefix Length

Is the number of 1-bits in the subnet mask. Example: 255.255.0.0 → /16. It simply counts the 1s. We use this slash notation to simplify dotted decimals in writing subnet masks (255.255.255.0 → /24).

AND

It means both must be TRUE to output TRUE. Example: 1 AND 1 = 1; 0 AND 1 = 0

Block Size

It means how wide each subnet is - the size of the entire subnet range. It includes, 1 network address, 1 broadcast address, plus the usable host addresses in between. Formula = 256 - Subnet Mask Value. You only compute this when the subnet mask splits an octet (ex /28, /25/…)

Number of Subnets

Used when subnetting a network. Formula = 2^{borrowed_bits}