modul8-Network Layer Overview Quiz

Study Notes

OSI Layer 3 facilitates end-to-end communication across multiple networks (routing).
Key protocols include IPv4, IPv6, routing protocols (e.g., OSPF), and ICMP.

Connectionless: No established session before data transmission.
Best Effort (Unreliable): No guarantee of packet delivery.
Media Independent: Operates across various physical media (copper, fiber, wireless).
IPv4 Packet Fields:
- Version (4 bits = 0100 identifying IPv4)
- DS or DiffServ (Quality of Service priority)
- TTL (Time to Live; decrements at each router)
- Protocol (identifies the next layer; e.g., 6 = TCP, 17 = UDP)
- Source & Destination IPs (32-bit addresses)
- Header Checksum (header integrity check)

128-bit addresses (significantly more than IPv4).
Simplified header (fixed 40 bytes).
Eliminates need for Network Address Translation (NAT) due to extensive address space.
IPv6 Packet Fields:
- Version (4 bits = 0110)
- Traffic Class (similar to DiffServ)
- Flow Label (for specific QoS handling)
- Payload Length
- Next Header (similar to IPv4 Protocol field)
- Hop Limit (similar to IPv4 TTL)
- Source & Destination 128-bit IPv6 addresses

A host's routing table determines packet destination:
- Local network: Sent directly.
- Remote network: Forwarded to the default gateway (router).
Default Gateway: Router interface on the same network as the host; used for routing to other networks.

Routers use routing tables to forward packets:
- Directly connected networks: Learned from active interfaces.
- Remote networks: Learned through static routes or dynamic routing protocols (OSPF, EIGRP).
- Default route: For unknown destinations ("gateway of last resort").
Routing Types:
- Static Routing: Manually configured routes; require updates for network changes.
- Dynamic Routing: Routers automatically share info and adjust to changes in network topology.