About this interactive
The lesson's Layer 3 in five facts:
- **Packet switching:** data is cut into packets, and each can take its own route. If a link goes down or gets busy, routers send packets another way.
- **Fragmentation:** if a packet is too big for the next link (its MTU), it is split into fragments. In IPv4 they are put back together only at the final destination.
- **Routing:** each router reads the destination address and picks the next hop. That is its whole job.
- **Connectionless:** routers keep no record of who is talking to whom; each packet is handled on its own.
- **Best effort:** a router drops a damaged or unroutable packet and fixes nothing. Resending lost data is left to upper-layer protocols at the two ends.
What you'll learn
- Predict how a packet-switched network handles a failed or busy link, a packet too big for the next link, and packets that arrive out of order
- Predict what Layer 3 does and leaves to other layers: routers read the destination address and forward, connectionless and best effort, with no repair and no resend
Aligned to
CompTIA Network+
1.1
Explain concepts related to the Open Systems Interconnection (OSI) reference model.
Cisco CCST Networking
1.1
Identify the fundamental conceptual building blocks of networks
4.4
Explain basic routing concepts
Key terms
- Network Layer
- Layer 3 of the OSI model, responsible for logical addressing and routing data packets between networks.
- Packet Switching
- A communication method that breaks data into packets and sends them independently across a network, potentially via different routes.
- Fragmentation
- The process of breaking a packet into smaller pieces when its size exceeds the maximum transmission unit of a network link, with reassembly occurring at the destination.
- Maximum Transmission Unit
MTU
- The largest size of a packet or frame that can be transmitted over a network link without fragmentation, typically 1500 bytes for Ethernet. When packets exceed the MTU, they must be fragmented at Layer 3 or the sender must reduce the packet size via Path MTU Discovery.
- Packet
- A unit of data formatted for transmission over a network, containing a header, payload, and sometimes a trailer.
- Next Hop
- The IP address of the immediately adjacent router that a packet is forwarded to on the way toward its final destination. A router's routing table entry for each network destination includes the next-hop address so the router knows where to send the packet.
Topics
Network Layer
Layer 3
Packet Switching
Fragmentation
Best Effort
Interactive
Predict
About TechKnowSurge
TechKnowSurge builds IT and cybersecurity professionals through hands-on, concept-first training built around real understanding — not memorization. Free interactive tools, structured programs, and 25+ years of real-world experience, all in one place.
Explore free tools and programs →