Core Networking · Study deck

IPv4 Addressing Fundamentals

Picture a replacement camera that receives an address but cannot reach its recorder.

Packet Pete is your guide for this deck.

addripv4

Packet Pete, the module guide, in a scene from this chapter.

After studying this chapter

Learning objectives

Follow this chapter path with evidence at each boundary.

Name the system boundary.
Record the evidence needed there.
Keep the next decision tied to the source.

Read a 32-bit address and prefix. Decide whether a destination is local or needs a gateway. Trace the route and policy for a camera-to-recorder flow.

Major section

Start With Where the Device Lives

The four visible numbers are not enough; its local boundary and route may be wrong.

Internet Protocol means a system for addressing and routing packets.
IPv4 means version 4 of that system.
A gateway means the boundary device that forwards traffic beyond the local network.
This runway does not prove identity, trust, or permission.

Major section

Overview: An IPv4 Address Names a Host in a Network Context

The split between network and host is decided by how many of those bits the mask claims, and it does not have to fall on a dot.

The last two rows are not host ranges at all; they hold multicast groups and a reserved block.

IPv4 is a 32-bit address. Dotted-decimal notation is a human-readable view of those bits.

Major section

Practitioner: Plan Subnets Around Device Groups and Traffic Rules

Each row shows one address with its mask written out in bits.

Every 1 claims a bit for the network, and every 0 leaves it to the host.
The /16 row makes this easy to see: the first sixteen bits are 1, so the mask reads 255.255.0.0.

IPv4 subnet mask showing how a 32-bit mask divides an address into network and host portions. — The subnet mask determines whether two IPv4 addresses are local peers or require a gateway.

Major section

Under the Hood: Packets Carry Addresses, Routers Use Prefixes

The grid is 20 bytes at minimum, drawn as rows four bytes wide.

The middle rows carry identification, flags and fragment offset for reassembly, then time-to-live and protocol.
Protocol tells the receiver whether TCP, UDP or ICMP is inside.

The IPv4 header carries source and destination addresses, TTL, protocol, length, fragmentation fields, and checksum information.

Major section

Place a Camera on the Correct IPv4 Street

The visible block labels place the camera and recorder on different subnets.

Name the system boundary.
Record the evidence needed there.
Keep the next decision tied to the source.

Camera 192.168.10.70/26 → 192.168.10.64/26, ordinary hosts .65–.126; recorder 192.168.10.20/26 → 192.168.10.0/26, ordinary hosts .1–.62; different subnets, route required.

Deck summary

Key takeaways

The four visible numbers are not enough; its local boundary and route may be wrong.

The split between network and host is decided by how many of those bits the mask claims, and it does not have to fall on a dot.
Each row shows one address with its mask written out in bits.
The grid is 20 bytes at minimum, drawn as rows four bytes wide.
For a /26 prefix, 26 bits name the network and 6 bits remain for hosts.

Retrieval practice

Recall check 1 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q1What makes an IPv4 address usable in an IoT network?

AThe device has an address, a mask or prefix, and a gateway decision for non-local traffic.

BThe address is valid because it has four decimal numbers in the standard IPv4 format.

CThe address starts with 192, because that always means it is reachable.

DThe address is public, because private addresses cannot be used by IoT devices.

Show answer

Answer: A IPv4 troubleshooting starts with the full context: address, prefix, local subnet, gateway, and any reserved-address role.

Retrieval practice

Recall check 2 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q2A sensor is configured as 172.20.15.45 with mask 255.255.255.0 and cannot reach a server at 172.20.30.10. Link status is up. What first routing fact follows from the given mask?

AThe /24 mask places the server outside the sensor's local subnet.

BThe 172.20 range is multicast and unusable for private devices.

CPrivate addresses cannot route to another private subnet.

DAddress exhaustion prevents the existing server from responding.

Show answer

Answer: A A subnet mask controls local reachability.

Retrieval practice

Recall check 3 of 3

Packet Pete says: answer from memory, then check your reasoning.

Q3Why does a subnet plan matter to routers and firewalls, not just to humans?

AThey act on address prefixes, next hops, and policy rules.

BThey infer device type from the text of an IPv4 address.

CThey use subnets as documentation without forwarding impact.

DThey replace route tables with each packet's TTL value.

Show answer

Answer: A A usable IPv4 plan connects human inventory, device groups, prefixes, gateways, and firewall policies.

Print reference

Answers

Answer key.

A · IPv4 troubleshooting starts with the full context: address, prefix, local subnet, gateway, and any reserved-address role.
A · A subnet mask controls local reachability.
A · A usable IPv4 plan connects human inventory, device groups, prefixes, gateways, and firewall policies.

A · Address, prefix, and gateway decision. A · The /24 server is outside the local subnet. A · Routers and firewalls use prefixes, next hops, and policy.