IPv6 vs IPv4 Networking Concepts

Network Layer Characteristics

• The network layer provides services for end devices to exchange data
• IPv4 and IPv6 are the main network layer communication protocols
• The network layer works with addressing end devices, encapsulation, routing, and de-encapsulation

IP Encapsulation

• IP encapsulates the transport layer segment
• Either an IPv4 or IPv6 packet can be used without impacting layer 4
• All layer 3 devices will examine an IP packet as it traverses the network
• IP addressing doesn't change from source to destination
• NAT will change addressing, but it will be discussed later

Characteristics of IP

• IP is designed with low overhead and can be described as connectionless, best effort, and media independent

Connectionless

• IP does not establish a connection with the destination before a packet is sent
• No control information is needed, which includes synchronizations and acknowledgments
• Pre-notifications aren't sent by IP; the destination receives the packet upon arrival
• If connection-oriented traffic is needed, another protocol, such as TCP at the transport layer, will handle it

Best Effort

• IP does not guarantee packet delivery
• IP has reduced overhead due to the absence of a mechanism for resending lost data
• IP does not expect acknowledgments
• IP lacks awareness if the destination device is operational or has successfully received the packet

Media Independent

• IP cannot manage or fix undelivered or corrupt packets
• IP is unable to retransmit after errors or realign out-of-sequence packets
• IP relies on other protocols for unreliability functions
• IP functions with any media type
• IP doesn't concern itself with the type of frame required at the data link layer or the media type at the physical layer
• Transmission can occur over copper wire, fiber optic cables, or wireless connections
• The network layer will estalish the Maximum Transmission Unit (MTU).
• The MTU Size is established by the network layer based on information from the data link layer.
• Fragmentation is when Layer 3 splits the IPv4 packet into smaller units.
• Fragmentation causes latency.
• IPv6 does not fragment packets.
• Routers that switch from ethernet to slower WAN that uses smaller MTU.

IPv4 Packet Header

• IPv4 is the primary communication protocol for the network layer
• The network header ensures packets travel to the correct destination
• The network header contains information for network layer processing
• Layer 3 devices use the header information to handle the packet

IPv4 Packet Header Fields

• The IPv4 network header is in binary
• It contains several fields of information
• Diagrams are read from left to right, four bytes per line
• The source and destination fields are the two most important fields

Significant Fields in the IPv4 Header

• Version: Indicates IPv4 as opposed to IPv6, represented by a 4-bit field with a value of 0100
• Differentiated Services: Used for Quality of Service (QoS)
• This can either be the DiffServ (DS) field or the older IntServ or Type of Service (ToS)
• Header Checksum: Used to detect corruption in the IPv4 header
• Time to Live (TTL): Functions as a Layer 3 hop count; packets are discarded by the router when it becomes zero
• Protocol: Identifies the next-level protocol, such as ICMP, TCP, or UDP
• Source IPv4 Address: A 32-bit address representing the sender's address
• Destination IPv4 Address: A 32-bit field indicating the intended recipient's address

Limitations of IPv4

• IPv4 has three major limitations: IPv4 address depletion, lack of end-to-end connectivity, and increased network complexity
• Private addressing and NAT were created because of a lack of end-to-end connectivity
• IPv4 address depletion: The world has basically ran out of IPv4 Addressses
• NAT (Network Address Translation) was meant as a temporary solution and causes latency and troubleshooting issues

IPv6 Overview

• IPv6 overcomes the limitations of IPv4
• IPv6 was developed by the Internet Engineering Task Force (IETF)
• Improvements of IPv6
  • Increased address space based on 128 bits
  • IPv6 has 340 Undecillion Addresses compared to IPv4 which has 4 billion
  • Improved packet handling, simplified header with fewer fields
  • No need for NAT due to a the huge amount of addresses

Fields in the IPv6 Packet Header

• The IPv6 header is simplified, but not smaller; it is fixed at 40 bytes long
• Several IPv4 fields were removed to improve performance
• Removals to improve performance include flag, fragment offset, and header checksum

Significant Fields in the IPv6 Header

• Version: Indicates the packet is IPv6, identified by a 4-bit field with a value of 0110
• Traffic Class: Used for Quality of Service (QoS)
• Flow Label: Informs devices how to handle identical flow labels, using a 20-bit field
• Payload Length: A 16-bit field specifying the length of the data portion or payload of the IPv6 packet
• Next Header: Indicates the next-level protocol such as ICMP, TCP, or UDP
• Hop Limit: Replaces the TTL field and functions as a Layer 3 hop count
• Source IPv4 Address: Consists of a 128-bit source address
• Destination IPv4 Address: A 128-bit address representing the recipient's address

Host Forwarding Decision

• Packets are always created at the source. Each host device has its own routing table
• A host will send packets to itself (127.0.0.1 for IPv4, ::1 for IPv6), local hosts on the same LAN, or remote hosts not on the same LAN
• The source device knows if the destination is local or remote
• The method of determination for IPv4 is the source matching its own IP address and subnet mask with the destination IP address
• The method of determiniation of IPv6 is matching network addresses with the local routers prefix that it advertises
• Local traffic is dumped out of the host interface and traffic is handled by an intermediary device
• Remote traffic os directly forwarded to the default gateway of the LAN

Default Gateway

• A router or layer 3 switch can act as a default gateway (DGW)
• Features of a DGW
  • It has to have an IP address in the same range as the rest of the LAN
  • It handles data flowing from the LAN and handles off traffic
  • Can route traffic to different networks
  • If a device lacks a DGW or has a bad DGW, its traffic will not be able to leave the LAN

A Host Routes to the Default Gateway

• The host knows the default gateway, whether statically or through DHCP in IPv4
• IPv6 sends the DGW through a router solicitation (RS) or it can be configured manually
• A DGW is a static route and will be a last resort route in the routing table
• Every device on the LAN needs the DGW of the route if they want to remotely sent traffic

Host Routing Tables

• On Windows, route print or netstat -r will displays the PC routing table
• Interface list, IPv4 routing table, and IPv6 routiung table are the three sections displayed by those commands
• Interface List has all potential interfaces and MAC addressing

Router Packet Forwarding Decision

• When the router receives frames from the host device, it makes the best route option
• Packet arrives on the Gigabit Ethernet 0/0/0 interface of router R1
• R1 de-encapsulates the Layer 2 Ethernet header and trailer
• Router R1 examines the destination IPv4 source address and searches for the best match in its IPv4 routing table, the router entry indicates this packet is to be forwarded to Router R2
• Router R1 encapsulates the packet into a new Ethernet header and trailer and forwards the packet for the to the next hop router R2

IP Router Routing Table

There are three types of routes for a router's routing table: Directly connected, remote, and default route

• Directly connected routes are automatically added by the router if the interface is active with an address
• Remote routes do not have a direct connection, and are learned manually with a static route, or dynamically by a routing protocol sharing info
• Default route forwards traffic toward a specific direction when there's no match in the routing table

Static Routing

• Static Route Characteristics: Must be configured and adjusted manually in the topology by an administrator, good for small non-redundant networks
• Static Routing can often be used with a dynamic routing protocol to configure a default route

Dynamic Routing

• Dynamic routes find remote networks, maintain up-to-date information, choosing the best path to destination, and finding new best paths when the is a topology change
• Dynamic routing can share static default routes with other routers

Introduction to an IPv4 Routing Table

• The show ip route command displays the following source routes which includes the local interface, connected network, static route, OSPF, and EIGRP
• The show ip route command can display directly connected routes with C, and L, remote routes with O, D, etc, and default routes with S*

Explore the differences between IPv6 and IPv4, including address space, header structure, and the reasons for IPv6's development. Learn about routing tables, default gateways, and static vs dynamic routing for effective network management.