IPv4 addresses are 32-bit numbers that are typically displayed in dotted decimal notation and contains two primary parts: the network prefix and the host number. The topics below describes the IPv4 Classful Addressing, IPv4 Dotted Decimal Notation, IPv4 Subnetting, IPv4 Variable-Length Subnet Masks, understanding IP Version 6, IPv6 address types and use of them in Junos OS RX Series Services Gateway, and configuration of inet6 IPv6 Protocol Family. Show
Understanding IPv4 AddressingIPv4 addresses are 32-bit numbers that are typically displayed in dotted decimal notation. A 32-bit address contains two primary parts: the network prefix and the host number. All hosts within a single network share the same network address. Each host also has an address that uniquely identifies it. Depending on the scope of the network and the type of device, the address is either globally or locally unique. Devices that are visible to users outside the network (webservers, for example) must have a globally unique IP address. Devices that are visible only within the network must have locally unique IP addresses. IP addresses are assigned by a central numbering authority called the Internet Assigned Numbers Authority (IANA). IANA ensures that addresses are globally unique where needed and has a large address space reserved for use by devices not visible outside their own networks. This topic contains the following sections:
IPv4 Classful AddressingTo provide flexibility in the number of addresses distributed to networks of different sizes, 4-octet (32-bit) IP addresses were originally divided into three different categories or classes: class A, class B, and class C. Each address class specifies a different number of bits for its network prefix and host number:
In binary format, with an 00000000 xxxxxxxx xxxxxxxx xxxxxxxx (Class A) 00000000 00000000 xxxxxxxx xxxxxxxx (Class B) 00000000 00000000 00000000 xxxxxxxx (Class C) Because each bit ( 111 110 101 100 011 010 001 000 In each IP address class, the number of host-number bits raised to the power of 2 indicates how many host numbers can be created for a particular network prefix. Class A addresses have 224 (or 16,777,216) possible host numbers, class B addresses have 216 (or 65,536) host numbers, and class C addresses have 28 (or 256) possible host numbers. IPv4 Dotted Decimal NotationThe 32-bit IPv4 addresses are most often expressed in dotted decimal notation, in which each octet (or byte) is treated as a separate number. Within an octet, the rightmost bit represents 20 (or 1), increasing to the left until the first bit in the octet is 27 (or 128). Following are IP addresses in binary format and their dotted decimal equivalents: 11010000 01100010 11000000 10101010 = 208.98.192.170 01110110 00001111 11110000 01010101 = 118.15.240.85 00110011 11001100 00111100 00111011 = 51.204.60.59 IPv4 SubnettingBecause of the physical and architectural limitations on the size of networks, you often must break large networks into smaller subnetworks. Within a such a subnetted network, each interface requires its own network number and identifying subnet address. Note: The IP routing world has shifted to Classless Inter-Domain Routing (CIDR). As its name implies, CIDR eliminates the notion of address classes and simply conveys a network prefix along with a mask. The mask indicates which bits in the address identify the network (the prefix). This document discusses subnetting in the traditional context of classfull IP addresses. Figure 1 shows a network comprised of three subnets. Figure 1: Subnets in a Network
Figure 1 shows three devices connected to the Alpha subnet on the
left, three devices connected to the Beta subnet on the right, and a third subnet named Gamma that interconnects the left and right subnets over a WAN link. Collectively, the six devices and three subnets are contained within the larger class B network prefix. In this example, the organization is assigned the network prefix In addition to sharing the class B
network prefix (the first two octets), each subnet shares the third octet. Because we are using a /24 network mask in conjunction with a class B address, the third octet identifies the subnet. All devices on a subnet must have the same subnet address. In this case, the alpha subnet has the IP address Taking one of these subnets as an example, the Beta subnet address 10101100 . 00010000 . 00000010 . xxxxxxxx Because the first 24 bits in the 32-bit address identify the subnet, the last 8 bits are available to assign to hosts attachments on each subnet. To reference a subnet, the address is written as IPv4 Variable-Length Subnet MasksTraditionally, subnets were divided by address class. Subnets had either 8, 16, or 24 significant bits, corresponding to 224, 216, or 28 possible hosts. As a result, an entire /16 subnet had to be allocated for a network that required only 400 addresses, wasting 65,136 (216 – 400 = 65,136) addresses. To help allocate address spaces more efficiently, variable-length subnet masks (VLSMs) were introduced. Using VLSM, network architects can allocate more precisely the number of addresses required for a particular subnet. For example, suppose a network with the prefix To accommodate 18 devices, the first subnet must have 25 (32)
host numbers. Having 5 bits assigned to the host number leaves 27 bits of the 32-bit address for the subnet. The IP address of the first subnet is therefore 11000000 . 00001110 . 00010001 . 100xxxxx The subnet mask includes 27 significant digits. To create the second subnet of 46 devices, the network must accommodate 26 (64) host numbers. The IP address of the second subnet is 11000000 . 00001110 . 00010001 . 01xxxxxx By assigning address bits within the larger Understanding IPv6 Address Space, Addressing, Address Format, and Address Types
Understanding IP Version 6 (IPv6)The ongoing expansive growth of the Internet and the need to provide IP addresses to accommodate it—to support increasing numbers of new users, computer networks, Internet-enabled devices, and new and improved applications for collaboration and communication—is escalating the emergent use of a new IP protocol. IPv6, with its robust architecture, was designed to satisfy these current and anticipated near future requirements. IP version 4 (IPv4) is widely used throughout the world today for the Internet, intranets, and private networks. IPv6 builds upon the functionality and structure of IPv4 in the following ways:
IPv6 addresses consist of 128 bits, instead of 32 bits, and include a scope field that identifies the type of application suitable for the address. IPv6 does not support broadcast addresses, but instead uses multicast addresses for broadcast. In addition, IPv6 defines a new type of address called anycast. Understanding IPv6 Address Types and How Junos OS for SRX Series Services Gateway Uses ThemIP version 6 (IPv6) includes the following types of addresses:
IPv6 Address ScopeUnicast and multicast IPv6 addresses support address scoping, which identifies the application suitable for the address. Unicast addresses support global address scope and two types of local address scope:
Multicast addresses support 16 different types of address scope, including node, link, site, organization, and global scope. A 4-bit field in the prefix identifies the address scope. IPv6 Address StructureUnicast addresses identify a single interface. Each unicast address consists of Multicast addresses identify a set of interfaces. Each multicast address consists of the first 8 bits of all 1s, a 4-bit flags field, a 4-bit scope field, and a 112-bit group ID: 11111111 | flgs | scop | group ID The first octet of 1s identifies the address as a multicast address. The flags field identifies whether the multicast address is a well-known address or a transient multicast address. The scope field identifies the scope of the multicast address. The 112-bit group ID identifies the multicast group. Similar to multicast addresses, anycast addresses identify a set of interfaces. However, packets are sent to only one of the interfaces, not to all interfaces. Anycast addresses are allocated from the normal unicast address space and cannot be distinguished from a unicast address in format. Therefore, each member of an anycast group must be configured to recognize certain addresses as anycast addresses. Understanding IPv6 Address Space, Addressing, and Address TypesAddressing is the area where most of the differences between IP version 4 (IPv4) and IPv6 exist, but the changes are largely about the ways in which addresses are implemented and used. IPv6 has a vastly larger address space than the impending exhausted IPv4 address space. IPv6 increases the size of the IP address from the 32 bits that compose an IPv4 address to 128 bits. Each extra bit given to an address doubles the size of the address space. IPv4 has been extended using techniques such as Network Address Translation (NAT), which allows for ranges of private addresses to be represented by a single public address, and temporary address assignment. Although useful, these techniques fall short of the requirements of novel applications and environments such as emerging wireless technologies, always-on environments, and Internet-based consumer appliances. In addition to the increased address space, IPv6 addresses differ from IPv4 addresses in the following ways:
Understanding IPv6 Address FormatAll IPv6 addresses are 128 bits long, written as 8 sections of 16 bits each. They are expressed in hexadecimal representation, so the sections range from 0 to FFFF. Sections are delimited by colons, and leading zeroes in each section may be omitted. If two or more consecutive sections have all zeroes, they can be collapsed to a double colon. IPv6 addresses consist of 8 groups of 16-bit hexadecimal values separated by colons (:). IPv6 addresses have the following format: aaaa:aaaa:aaaa:aaaa:aaaa:aaaa:aaaa:aaaa Each 3FFE:0000:0000:0001:0200:F8FF:FE75:50DF You can omit the leading zeros of each 16-bit group, as follows: 3FFE:0:0:1:200:F8FF:FE75:50DF You can compress 16-bit groups of zeros to double colons (::) as shown in the following example, but only once per address: 3FFE::1:200:F8FF:FE75:50DF An IPv6 address prefix is a combination of an IPv6 prefix (address) and a prefix length. The prefix takes the form ipv6-prefix/prefix-length and represents a block of address space (or a network). The ipv6-prefix variable follows general IPv6 addressing rules. The prefix-length variable is a decimal value that indicates the number of contiguous, higher-order bits of the address that make up the network portion of the address. For example, 10FA:6604:8136:6502::/64 is a possible IPv6 prefix with zeros compressed. The site prefix of the IPv6 address 10FA:6604:8136:6502::/64 is contained in the left most 64 bits, 10FA:6604:8136:6502. For more information on the text representation of IPv6 addresses and address prefixes, see RFC 4291, IP Version 6 Addressing Architecture. LimitationsSRX300, SRX320, SRX340, SRX345, SRX380, and SRX550HM devices have the following limitations:
Configuring the inet6 IPv6 Protocol FamilyIn configuration commands, the protocol family for IPv6 is named Note: On SRX Series devices, on configuring identical IPs on a single interface, you will not see a warning message; instead, you will see a syslog message. The following example shows the CLI commands you use to configure an IPv6 address for an interface: [edit]
user@host# show interfaces
ge-0/0/0 {
unit 0 {
family inet {
address 10.100.37.178/24;
}
}
}
[edit]
user@host# set interfaces ge-0/0/0 unit 0 family ?
Possible completions:
+ apply-groups Groups from which to inherit configuration data
+ apply-groups-except Don't inherit configuration data from these groups
> ccc Circuit cross-connect parameters
> ethernet-switching Ethernet switching parameters
> inet IPv4 parameters
> inet6 IPv6 protocol parameters
> iso OSI ISO protocol parameters
> mpls MPLS protocol parameters
> tcc Translational cross-connect parameters
> vpls Virtual private LAN service parameters
[edit]
user@host# set interfaces ge-0/0/0 unit 0 family inet6 address 8d8d:8d01::1/64
user@host# show interfaces
ge-0/0/0 {
unit 0 {
family inet {
address 10.100.37.178/24;
}
family inet6 {
address 8d8d:8d01::1/64;
}
}
}
What type of address identifies a network interface?The IPv4 address is a 32-bit number that uniquely identifies a network interface on a machine. An IPv4 address is typically written in decimal digits, formatted as four 8-bit fields that are separated by periods.
What type of device is used to transfer packets between different networks?A router directs data requests from one network to another. Routers examine incoming packets to determine the appropriate destination IP address and then forward the packet to that destination. A router can also enable internet access through its connection to a modem, or as a combined modem-router.
Which protocol allows people to use names labels to address network resources rather than numeric addresses?The domain name system (DNS) is a naming database in which internet domain names are located and translated into Internet Protocol (IP) addresses. The domain name system maps the name people use to locate a website to the IP address that a computer uses to locate that website.
What protocol is usually used to provide logical network addressing on networks?TCP (Transmission Control Protocol) - the Internet protocol's main transport layer protocol. It also provides addressing services at the network layer. DNS (Domain Name System) - a distributed database system that works at the transport layer to provide name-to-address mapping for client applications.
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What type of address identifies a network interface in the context of the local network segment only?
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