Guide to TCP/IP Fourth Edition Chapter 2: IP Addressing and Related Topics
Objectives Describe IP addressing, anatomy and structures, and addresses from a computer s point of view Recognize and describe IPv4 addressing and address classes, describe the nature of IPv4 address limitations, and define the terms subnet, supernet, subnetting, and supernetting Describe how to obtain public and private Internet addresses Explore IPv4 addressing schemes 2
Objectives (cont'd.) Describe the nature of IPv4 address limitations and why IPv6 is needed Discuss new and enhanced IPv6 features Recognize and describe IPv6 addressing schemes, features, and capacities Describe the impediments involved in transitioning from IPv4 to IPv6 3
IP Addressing Basics Computers deal with network addresses as bit patterns IP uses a three-part addressing scheme Symbolic Example support.dell.com Logical numeric Example 172.16.1.10 Physical numeric Six-byte numeric address, burned into firmware (on a chip) by network interface manufacturers 4
IP Addressing Basics (cont'd.) Address Resolution Protocol (ARP) Permits computers to translate numeric IP addresses to MAC layer addresses ReverseARP (RARP) Translates MAC layer addresses into numeric IP addresses 5
IPv4 Addressing Numeric IPv4 addresses Dotted decimal notation Take the form n.n.n.n, where n is guaranteed to be between 0 and 255 Each number is an 8-bit number called an octet Duplication is not allowed 6
IPv4 Address Classes IP addresses Subdivided into five classes: Class A to Class E For first three classes octets are divided as follows Class A n. h.h.h Class B n.n. h.h Class C n.n.n. h n = network, h = host 7
IP Address Classes (cont'd.) Address Classes D and E are for special uses Class D addresses Multicast communications Class E addresses Reserved entirely for experimental use 8
Network, Broadcast, Multicast, and Other Special IPv4 Addresses Network address Any IP address where all host bits are 0 Broadcast address Address that all hosts on a network must read Broadcast traffic Seldom forwarded from one physical network to another 9
Broadcast Packet Structures IPv4 broadcast packets have two destination address fields Data Link layer destination address field Destination network address field 10
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Broadcast Packet Structures (cont d.) Multicast Packet and Address Structures Host listens on the multicast and broadcast addresses besides its own IP gateway Router or other device that will forward traffic to the host s physical network The Internet Corporation for Assigned Names and Numbers (ICANN) Allocates multicast addresses on a controlled basis 12
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Broadcast Packet Structures (cont d.) 14
IPv4 Networks and Subnets Masks Subnet mask Special bit pattern that blocks off the network portion of an IP address with an all-ones pattern Default masks for Classes A, B, and C 15
IPv4 Subnets and Supernets Subnetting Stealing (borrowing) bits from the host portion to further subdivide the network portion of an address Supernetting Stealing bits from network portion Using them to create a single, larger contiguous address space for host addresses 16
IPv4 Subnets and Supernets (cont d.) Types of subnet masking techniques Constant-length subnet masking (CLSM) Variable-length subnet masking (VLSM) In a VLSM addressing scheme Different subnets may have different extended network prefixes 17
IPv4 Subnets and Supernets (cont d.) Bitcricket IP Calculator Free subnet mask calculator from WildPackets First to support IPv6 Classless Inter-Domain Routing (CIDR) routes can also be calculated SolarWinds IP Subnet Calculator Provides address details such as reverse DNS resolution and response time 18
Classless Inter-Domain Routing in IPv4 Limitations Network addresses must be contiguous When address aggregation occurs CIDR address blocks work best when they come in sets that are greater than 1 and equal to some lowerorder bit pattern that corresponds to all 1s Addresses commonly applied to Class C addresses To use a CIDR address on any network Routers in routing domain must understand CIDR notation 19
Public Versus Private IPv4 Addresses Private IP addresses ranges May be in the form of IP network addresses Address masquerading May be performed by boundary devices that include proxy server capabilities Private IP address limitation Some IP services require a secure end-to-end connection 20
Public Versus Private IPv4 Addresses (cont d.) 21
Public Versus Private IPv4 Addresses Public IP addresses (cont'd.) Remain important for identifying all servers or services that must be accessible to the Internet Most organizations need public IP addresses only for two classes of equipment Devices that permit organizations to attach networks to the Internet Servers designed to be accessible to the Internet 22
Managing Access To IPv4 Address Reverse proxying Information Permits the proxy server to front for servers inside the boundary Important service that proxy server provides Manages what source addresses appear in outbound packets that pass through it 23
Obtaining Public IP Addresses Public IP addresses Issued by ISPs IP renumbering Switching addresses on every machine that uses address from old ISP to unique address obtained from new ISP ICANN Manages all IP-related addresses, protocol numbers, and well-known port addresses Assigns MAC layer addresses for use in network interfaces 24
IPv4 Addressing Schemes IP addressing scheme constraints Number of physical locations Number of network devices at each location Amount of broadcast traffic at each location Availability of IP addresses Delay caused by routing from one network to another 25
The Network Space Application Specific Integrated Circuits (ASICs) Hardware used by switches to make decisions Layer-3 switch Implements the layer-3 logic from the software into its own ASICs Allows you to partition a large network into many smaller subnets with almost no loss of performance 26
The Host Space Reasons for using binary boundaries You may want to implement Layer 3 switching to reduce the broadcast traffic One day you will want to classify your traffic to apply Quality of Service (QoS) or policies of some sort Can be applied to firewall rules 27
The End of the IPv4 Address Space Address space saving techniques Classless Inter-Domain Routing (CIDR) Trade in existing IP network addresses RFC 1918 Reserves three ranges of IP addresses for private use Network Address Translation (NAT) Lets networks use private IP addresses internally and maps them to public IP address externally 28
Introducing IPv6 IPv6 Provides a vast abundance of IP addresses and better management of its address space Eliminates the need for NAT Has modernized routing support and natively allows for expansion along with the growing Internet Supports network security by using authentication and encryption extension headers 29
Request for Comments Pages and Depreciation Request for Comments (RFC) Describe the methods, innovations, and standards that are applied to every aspect of the Internet, including IPv6 RFC 5156 Contains a summary of various other RFCs regarding special usage of IPv6 addresses When reviewing RFCs Make special note of depreciated and obsolete information and documents 30
IPv6 Addressing IPv6 addresses 128 bits long String that uniquely identifies one single network interface on the global Internet Contains a network portion and a host portion Network and host portion depend on who s looking at it and where they are located 31
Address Format and Notation Addresses in IPv6 are also binary numbers Expressed using hexadecimal notation (00 FF) Broken up differently IPv6 uses groups of four 16-bit numbers called words, separated by a colon character (:) Examples: 1090:0000:0000:0000:0009:0900:210D:325F or 1090::9:900:210D:325F 32
Network and Host Address Portions Network prefix similar to CIDR Examples: 1090::9:900:210D:325F / 60 1018:FD0C:0:9:90:900:10BB:A / 24 33
Scope Identifier 4-bit field Limits the valid range for a multicast address Defines the portion of the Internet to which the multicast group pertains 34
Interface Identifiers IPv6 requires that every network interface have its own unique identifier Hardware vendors tend to use the modified EUI-64 format Software makers, including Microsoft, use the privacy format defined in RFC 4941 Having the right-hand portion of your IPv6 address based on the computer s MAC or hardware address presents a security concern 35
Interface Identifiers (cont d.) 36
Native IPv6 Addresses in URLs RFC 2732 (originally proposed in 1999) Describes a method to express IPv6 addresses in a form compatible with HTTP URLs Uses square brackets ([ and ]), to enclose a literal IPv6 address Example: http://[fedc:ba98:7654:3210:fedc:ba98:7654:321 0]:70/ 37
Address Types Special addresses Unspecified address All zeroes and can be represented as two colon characters (::) in normal notation Loopback allows a host on a network to check the operation of its own local TCP/IP protocol stack Multicast addresses Used to send an identical message to multiple hosts Anycast address Packets addressed to an anycast address go to the nearest single instance of that address 38
Address Types (cont d.) Unicast address Sent to one network interface Aggregatable global unicast address Can be combined with other addresses into a single entry in the router table Link-local address First 10 (leftmost) bits set to 1111111010 Site-local address First 10 (leftmost) bits set to 1111111011 39
Address Allocations IPv6 pre-allocates only about 15 percent of its available addresses Network Service Access Point (NSAP) addressing Holds 1/128 of all the IPv6 address space Unicast and anycast allocations Multicast allocations All IPv6 addresses beginning with 0xFF 40
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IPv6 Addressing and Subnetting Considerations In general IPv6 does not require subnetting Although possible Extent to which you can subnet an IPv6 address depends on the length of the prefix How you apportion the host addressing depends on the prefix length 42
The IPv4 to IPv6 Transition Transition technologies: Teredo tunneling ISATAP or Intra-Site Automatic Tunnel Addressing Protocol 6to4 tunneling NAT-PT (Network Address Translation-Protocol Translation) 43
Summary IP addresses Provide foundation for identifying individual network interfaces on TCP/IP networks IPv4 addresses Come in five classes named through E Classless Inter-Domain Routing (CIDR) Permits network-host boundary to fall away from octet boundaries Subnetting Permits additional bits to be taken from the host portion of a network 44
Summary (cont'd.) Address masquerading and address substitution Techniques used to hide internal network IP addresses from outside view Within the Class A, B, and C IP address ranges IETF has reserved private IP addresses or address ranges Internet Corporation For Assigned Names and Numbers (ICANN) Ultimate authority for obtaining public IP addresses The world has all but run out of IPv4 addresses 45
Summary (cont'd.) IPv6 introduces a number of improvements and updates to the IP protocol IPv6 supports three address types: unicast, multicast, and anycast IPv6 employs two private or local-use address schemes IPv6 prefix lengths define the number of bits apportioned to the network address and to the host address 46