Sem 2 Networking Programming Week 6 Network Layer

IPv6 Packet Header

• The IPv6 packet header has significant fields, including:
• Version: 4-bit field indicating IPv6
• Traffic Class: equivalent to DiffServ - DS field
• Flow Label: 20-bit field informing devices to handle identical flow labels the same way
• Payload Length: 16-bit field indicating the length of the data portion or payload
• Next Header: identifies the next level protocol, such as ICMP, TCP, or UDP

Media Independence

• IP is media independent, meaning it can be sent over any media type (copper, fiber, or wireless)
• The network layer establishes the Maximum Transmission Unit (MTU) based on control information from the data link layer
• Fragmentation occurs when Layer 3 splits the IPv4 packet into smaller units, causing latency; IPv6 does not fragment packets

IPv4 Packet Header

• The IPv4 packet header has significant fields, including:
• Version: 4-bit field indicating IPv4
• Differentiated Services: equivalent to DiffServ - DS field or the older IntServ - ToS or Type of Service
• Header Checksum: detects corruption in the IPv4 header
• Time to Live: Layer 3 hop count; when it reaches zero, the router discards the packet
• Protocol: identifies the next level protocol, such as ICMP, TCP, or UDP
• Source IPv4 Address: 32-bit source address
• Destination IPv4 Address: 32-bit destination address

Limitations of IPv4

• IPv4 has three major limitations:
• IPv4 address depletion
• Lack of end-to-end connectivity due to private addressing and NAT
• Increased network complexity due to NAT

IPv6 Overview

• IPv6 was developed by the Internet Engineering Task Force (IETF) to overcome the limitations of IPv4
• Improvements in IPv6 include:
• Increased address space based on 128-bit addresses
• Simplified header with fewer fields
• Elimination of the need for NAT due to the huge amount of available addresses

IPv6 Packet Header Fields

• The IPv6 header is simplified and fixed at 40 bytes or octets long
• Several IPv4 fields were removed to improve performance, including:
• Flag
• Fragment Offset
• Header Checksum
• New fields in the IPv6 header include:
• Hop Limit: replaces TTL field, Layer 3 hop count
• Source IPv6 Address: 128-bit source address
• Destination IPv6 Address: 128-bit destination address

Extension Headers

• IPv6 packets can contain extension headers (EH) that provide optional network layer information
• EH characteristics:
• Are optional
• Are placed between the IPv6 header and the payload
• May be used for fragmentation, security, mobility support, etc.

Host Routing and Forwarding

• Packets are always created at the source
• Each host device creates its own routing table
• A host can send packets to itself, local hosts, or remote hosts
• The source device determines whether the destination is local or remote
• The method of determination depends on the IP version:
• IPv4: uses IP address and subnet mask
• IPv6: uses the network address and prefix advertised by the local router

Default Gateway

• A router or layer 3 switch can be a default gateway
• Features of a default gateway (DGW) include:
• Having an IP address in the same range as the rest of the LAN
• Accepting data from the LAN and forwarding traffic off the LAN

Network Layer Characteristics

• The network layer provides services to allow end devices to exchange data
• IP version 4 (IPv4) and IP version 6 (IPv6) are the principle network layer communication protocols
• The network layer performs four basic operations:
• Addressing end devices
• Encapsulation
• Routing
• De-encapsulation

IP Encapsulation

• IP encapsulates the transport layer segment
• The IP packet is examined by all layer 3 devices as it traverses the network
• The IP addressing does not change from source to destination

Characteristics of IP

• IP is meant to have low overhead and can be described as:
• Connectionless
• Best Effort
• Media Independent