Chapter 5 Internet Addressing
Unfortunately, the ISO model predates work on the Internet, and does not describe the Internet protocols well. It contains layers not used by TCP/IP protocols. Because it was designed to describe protocols in a single network, the model does not describe the organization of TCP/IP protocols well.
5.3 IPv4 Subnet Addressing
When using subnet addressing, we think of a 32-bit IPv4 address as having an internet portion and a local portion, where the internet portion identifies a site, possibly with multiple physical networks, and the local portion identifies a physical network and host at that site.
5.3.1 Fixed Length Subnet Mask
5.3.2 Variable Length Subnet Mask
To allow maximum flexibility in choosing how to partition subnet addresses, the TCP/IP subnet standard permits variable-length subnetting in which a partition can be chosen independently for each physical network. Once a subnet partition has been selected, all machines on that network must honor it.
5.3.3 Classless Inter-Domain Routing
CIDR specifies that a manager should use slash notation to specify the mask. Syntactically, the format, which is sometimes called CIDR notation, consists of a starting address in dotted decimal followed by a mask size in slash notation. The format will be: x.x.x.x/y
5.4 IPv4 CIDR Blocks reserved for Private Networks
When using subnet addressing, we think of a 32-bit IPv4 address as having an internet portion and a local portion, where the internet portion identifies a site, possibly with multiple physical networks, and the local portion identifies a physical network and host at that site.
5.5 IPv6 Colon Hexadecimal Notation
First, colon hex notation allows zero compression in which a string of repeated zeros is replaced by a pair of colons. For example, the address: FF05:0:0:0:0:0:0:B3 can be written: FF05::B3
Second, colon hex notation incorporates dotted decimal suffixes; such combinations are intended to be used during the transition from IPv4 to IPv6. For example, the following string is a valid colon hex notation: 0:0:0:0:0:0:128.10.2.1
Finally, IPv6 extends CIDR-like notation by allowing an address to be followed by a slash and an integer that specifies a number of bits. For example, 12AB::CD30:0:0:0:0/60 specifies the first 60 bits of the address which is 12AB00000000CD3 in hexadecimal.
5.6 IPv6 Address Space Assignment
The first issue focuses on the practical problem of devising a hierarchy of authority. Unlike the current Internet, which uses a two-level hierarchy of network prefix (assigned by an ISP) and host suffix (assigned by an organization), the large address space in IPv6 permits amulti-level hierarchy or multiple hierarchies. Large ISPs can start with large blocks of addresses and assign subblocks to second-level ISPs, which can each assign subblocks from their allocation to third-level ISPs, and so on. The second issue focuses on router efficiency,
The above diagram mentioned about the prefixes used to divide the IPv6 address space into blocks and the purpose of each block.
5.7 Embedding IPv4 Addresses in IPv6 for transition
Embedding an IPv4 address in an IPv6 address will be used during the transition from IPv4 to IPv6 for two reasons. First, a computer may choose to upgrade from IPv4 to IPv6 software before it has been assigned a valid IPv6 address. Second, a computer running IPv6 software may need to communicate with a computer that runs only IPv4 software.
5.8 IPv6 Unicast Addresses and /64
IPv6 address is divided into three conceptual parts: a globally-unique prefix used to identify a site, a subnet ID used to distinguish among multiple physical networks at the destination site, and an interface ID used to identify a particular computer connected to the subnet.
5.9 IPv6 Interface Identifiers and MAC Addresses
IPv6 uses the term interface identifier (interface ID) rather than host identifier to emphasize that a host can have multiple interfaces and multiple IDs. Two examples will help clarify the concept. IEEE defines a standard 64-bit globally unique MAC address format known as EUI-64. As the figure shows, bits from the original MAC address are not contiguous in an IPv6 address. Instead, 16 bits with hexadecimal value FFFE are inserted in the middle. In addition, bit 6, which indicates whether the address has global scope, is changed from 0 to 1. Remaining bits of the address, including the group bit (labeled g), the ID of the company that manufactured the interface (labeled c), and the manufacturer’s extension are copied as shown.
5.8 Special Addresses
5.8.1 IPv4 Network Address
An IPv4 address with zero in the host portion is used to refer to the network itself.
5.8.2 IPv4 Directed Broadcast Address
Directed broadcast address that is sometimes called a network broadcast address. When used as a destination address, it refers to all computers on a network. The standard specifies that a host id of all 1s is reserved for directed broadcast
5.8.3 IPv4 Limited (Local Network) Broadcast Address
A limited broadcast means a packet is broadcast across the local network. The local broadcast address consists of thirty-two1s (hence, it is sometimes called the “all1s” broadcast address).
5.8.4 IPv4 Subnet Broadcast Address
A subnet broadcast address is used to broadcast on a single network within a site that uses subnetting. The address contains a network and subnet prefix and has all 1s in the host field.
5.8.5 IPv4 All-0s Source Address
An address that consists of thirty-two zero bits is reserved for cases where a host needs to communicate, but does not yet know its own IP address (i.e., at startup)
5.8.6 IPv4 Multicast Addresses
5.8.7 IPv4 Loopback Address
IPv4 reserves 127.0.0.0 / 8 for loopback testing; a packet destined to any host with prefix 127 stays within the computer and does not travel across a network.
5.8.8 Summary of IPv4 Special Addresses
5.8.9 IPv6 Multicast and Anycast Addresses
IPv6 designers decided to avoid broadcast and use only multicast. Therefore, IPv6 defines several reserved sets of multicast groups. Anycast addressing is designed to handle server replication. A provider can deploy a set of identical servers at arbitrary locations in the Internet. All servers in the set must offer exactly the same service, and all are assigned the same anycast address. Forwarding is set up so that a packet sent to the anycast address goes to the nearest server.
5.8.10 IPv6 Link-Local Addresses
IPv6 defines a set of prefixes for unicast addresses that are not globally valid. Instead, the prefixes are said to be locally scoped or to have link-local scope. That is, packets sent to the addresses are restricted to travel across a single network. The standard defines any IPv6 address that begins with the 10-bit binary prefix:
5.9 Weaknesses in Internet Addressing
If a host computer moves from one network to another, its internet address must change.
5.1 Universal Host Identifiers
Each host on an IPv4 internet is assigned a unique Internet address that is used in all communication with the host. To make forwarding efficient, a prefix of the address identifies a network and a suffix identifies a host on the network. The designers also decided to make IP addresses fixed size (32 bits was chosen for IPv4 and 128 bits for IPv6).
5.2 The Original IPv4 Classful Addressing SchemeEach host on an IPv4 internet is assigned a unique Internet address that is used in all communication with the host. To make forwarding efficient, a prefix of the address identifies a network and a suffix identifies a host on the network. The designers also decided to make IP addresses fixed size (32 bits was chosen for IPv4 and 128 bits for IPv6).
Unfortunately, the ISO model predates work on the Internet, and does not describe the Internet protocols well. It contains layers not used by TCP/IP protocols. Because it was designed to describe protocols in a single network, the model does not describe the organization of TCP/IP protocols well.
5.3 IPv4 Subnet Addressing
When using subnet addressing, we think of a 32-bit IPv4 address as having an internet portion and a local portion, where the internet portion identifies a site, possibly with multiple physical networks, and the local portion identifies a physical network and host at that site.
5.3.1 Fixed Length Subnet Mask
This terminology is used to CLASSFUL Addressing. Let us take a ClassFul Address whic belongs to CLASS A.
It is defaultly assumed to have a Mask as 8. Only 8 bits for Network &&& remaing 24 bits for Host.
5.3.2 Variable Length Subnet Mask
To allow maximum flexibility in choosing how to partition subnet addresses, the TCP/IP subnet standard permits variable-length subnetting in which a partition can be chosen independently for each physical network. Once a subnet partition has been selected, all machines on that network must honor it.
5.3.3 Classless Inter-Domain Routing
CIDR specifies that a manager should use slash notation to specify the mask. Syntactically, the format, which is sometimes called CIDR notation, consists of a starting address in dotted decimal followed by a mask size in slash notation. The format will be: x.x.x.x/y
5.4 IPv4 CIDR Blocks reserved for Private Networks
When using subnet addressing, we think of a 32-bit IPv4 address as having an internet portion and a local portion, where the internet portion identifies a site, possibly with multiple physical networks, and the local portion identifies a physical network and host at that site.
5.5 IPv6 Colon Hexadecimal Notation
First, colon hex notation allows zero compression in which a string of repeated zeros is replaced by a pair of colons. For example, the address: FF05:0:0:0:0:0:0:B3 can be written: FF05::B3
Second, colon hex notation incorporates dotted decimal suffixes; such combinations are intended to be used during the transition from IPv4 to IPv6. For example, the following string is a valid colon hex notation: 0:0:0:0:0:0:128.10.2.1
Finally, IPv6 extends CIDR-like notation by allowing an address to be followed by a slash and an integer that specifies a number of bits. For example, 12AB::CD30:0:0:0:0/60 specifies the first 60 bits of the address which is 12AB00000000CD3 in hexadecimal.
5.6 IPv6 Address Space Assignment
The first issue focuses on the practical problem of devising a hierarchy of authority. Unlike the current Internet, which uses a two-level hierarchy of network prefix (assigned by an ISP) and host suffix (assigned by an organization), the large address space in IPv6 permits amulti-level hierarchy or multiple hierarchies. Large ISPs can start with large blocks of addresses and assign subblocks to second-level ISPs, which can each assign subblocks from their allocation to third-level ISPs, and so on. The second issue focuses on router efficiency,
The above diagram mentioned about the prefixes used to divide the IPv6 address space into blocks and the purpose of each block.
5.7 Embedding IPv4 Addresses in IPv6 for transition
Embedding an IPv4 address in an IPv6 address will be used during the transition from IPv4 to IPv6 for two reasons. First, a computer may choose to upgrade from IPv4 to IPv6 software before it has been assigned a valid IPv6 address. Second, a computer running IPv6 software may need to communicate with a computer that runs only IPv4 software.
5.8 IPv6 Unicast Addresses and /64
IPv6 address is divided into three conceptual parts: a globally-unique prefix used to identify a site, a subnet ID used to distinguish among multiple physical networks at the destination site, and an interface ID used to identify a particular computer connected to the subnet.
5.9 IPv6 Interface Identifiers and MAC Addresses
IPv6 uses the term interface identifier (interface ID) rather than host identifier to emphasize that a host can have multiple interfaces and multiple IDs. Two examples will help clarify the concept. IEEE defines a standard 64-bit globally unique MAC address format known as EUI-64. As the figure shows, bits from the original MAC address are not contiguous in an IPv6 address. Instead, 16 bits with hexadecimal value FFFE are inserted in the middle. In addition, bit 6, which indicates whether the address has global scope, is changed from 0 to 1. Remaining bits of the address, including the group bit (labeled g), the ID of the company that manufactured the interface (labeled c), and the manufacturer’s extension are copied as shown.
5.8 Special Addresses
5.8.1 IPv4 Network Address
An IPv4 address with zero in the host portion is used to refer to the network itself.
5.8.2 IPv4 Directed Broadcast Address
Directed broadcast address that is sometimes called a network broadcast address. When used as a destination address, it refers to all computers on a network. The standard specifies that a host id of all 1s is reserved for directed broadcast
5.8.3 IPv4 Limited (Local Network) Broadcast Address
A limited broadcast means a packet is broadcast across the local network. The local broadcast address consists of thirty-two1s (hence, it is sometimes called the “all1s” broadcast address).
5.8.4 IPv4 Subnet Broadcast Address
A subnet broadcast address is used to broadcast on a single network within a site that uses subnetting. The address contains a network and subnet prefix and has all 1s in the host field.
5.8.5 IPv4 All-0s Source Address
An address that consists of thirty-two zero bits is reserved for cases where a host needs to communicate, but does not yet know its own IP address (i.e., at startup)
5.8.6 IPv4 Multicast Addresses
5.8.7 IPv4 Loopback Address
IPv4 reserves 127.0.0.0 / 8 for loopback testing; a packet destined to any host with prefix 127 stays within the computer and does not travel across a network.
5.8.8 Summary of IPv4 Special Addresses
5.8.9 IPv6 Multicast and Anycast Addresses
IPv6 designers decided to avoid broadcast and use only multicast. Therefore, IPv6 defines several reserved sets of multicast groups. Anycast addressing is designed to handle server replication. A provider can deploy a set of identical servers at arbitrary locations in the Internet. All servers in the set must offer exactly the same service, and all are assigned the same anycast address. Forwarding is set up so that a packet sent to the anycast address goes to the nearest server.
5.8.10 IPv6 Link-Local Addresses
IPv6 defines a set of prefixes for unicast addresses that are not globally valid. Instead, the prefixes are said to be locally scoped or to have link-local scope. That is, packets sent to the addresses are restricted to travel across a single network. The standard defines any IPv6 address that begins with the 10-bit binary prefix:
1111 1110 10
Routers honor link-local scoping rules. A router can respond to a link-local packet sent across a local network, but a router never forwards a packet that contains a link local address outside the specified scope.5.9 Weaknesses in Internet Addressing
If a host computer moves from one network to another, its internet address must change.
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