CIS 527

Lab 3 - Network Layer

Network Layer

• Transmit Packets Between Connected Networks
• Typically uses the Internet Protocol (IP) for Addressing
• Most Routers Operate at this Layer

IPv4 Packet Structure

IPv4 Addresses

• 32-bit Binary Numbers
• Unique Identifier on Network
• Usually Represented in Dot-Decimal Notation

Image Source: Wikipedia

Old - Classful Networks

• Network Determined by First 4 Bits
• Class A - 128 Networks, 16m Addresses Each
• Class B - 16k Networks, 1m Addresses Each
• Class C - 2m Networks, 256 Addresses Each
• Class D - Multicast

Image Source: TCP/IP Guide

Image Source: XKCD

New - Classless Inter-Domain Routing (CIDR)

• Introduces Subnet Masking
• Subnet Mask Defines Network & Host Portion of Address
• Much More Flexible & Scalable

Subnet Mask Example

IP:   192.168.  2.130 11000000.00000000.00000010.10000010
Mask: 255.255.255.  0 11111111.11111111.11111111.00000000
Net:  192.168.  2.  0 11000000.00000000.00000010.--------
Host:   0.  0.  0.130 --------.--------.--------.10000010

IP:   192.168.  2.130 11000000.00000000.00000010.10000010
Mask: 255.255.255.192 11111111.11111111.11111111.11000000
Net:  192.168.  2.128 11000000.00000000.00000010.10------
Host:   0.  0.  0.  2 --------.--------.--------.--000010

CIDR Notation

• IP Followed by Number of Leading 1s in Subnet Mask
• Example: 192.168.2.0/24
  • Network: 192.168.2.0
  • Subnet Mask: 255.255.255.0

CIDR Routing

Image Source: Wikipedia

Reserved Spaces

• 10.0.0.0/8 - Class A
• 172.16.0.0/12 - 16 × Class B
• 192.168.0.0/16 - 256 × Class C
• 127.0.0.0/8 - Loopback
• 169.254.0.0/16 - Link-Local
• 100.64.0.0/10 - Carrier-Grade NAT

Network Address Translation (NAT)

Image Source: TCP/IP Guide

IPv4 vs. IPv6

IPv4: 32-bit Addresses
2³² = 4,294,967,296

IPv6: 128-bit Addresses
2¹²⁸ = 340,282,366,920,938,463,463,
374,607,431,768,211,456
or 340 Undecillion addresses

IPv6 Packet Structure

Image Source: Wikipedia

IPv6 Addresses

• 128-bit Binary Numbers
• 8 Groups of 4 Hexadecimal Digits, Separated By Colons
• Representation May Be Simplified

IPv6 Address Reduction

• Omit Leading 0s
• Combine Consecutive Empty Groups With :: Once Per Address

2001:0db8:85a3:0000:0000:8a2e:0370:7334
2001: db8:85a3:   0:   0:8a2e: 370:7334
2001: db8:85a3    ::     8a2e: 370:7334
2001:db8:85a3::8a2e:370:7334

IPv6 Addressing

• Method Indicated by Prefix
• Each Method Uses a Different Format
• 001 - Global Unicast
• FE80 - Link-Local
• FC & FD - Unique-Local
• Many Reserved Ranges