This page describes general network concepts that you must
understand before you configure your ImageStream router. See the glossary linked
to our Other Resources
page for unfamiliar terms.
routers support packet routing using the IP protocol. The Internet Protocol (IP)
is a packet-based protocol used to exchange data over computer networks. IP provides
addressing and control information that allows data packets to be routed across
IP address descriptions
are found in RFC 1166, Internet Numbers. The Network Working Group maintains and
distributes the RFC documents. The American Registry for Internet Numbers (ARIN)
assigns IP addresses and network numbers to Internet service providers (ISPs),
who in turn provide to their customers a range of addresses appropriate to the
number of host devices on their network. The sections that follow describe the
various types of IP addresses, how addresses are given, and routing issues related
IP Address Notation
IP addresses are written
in dotted decimal notation consisting of four numbers separated by dots (periods).
Each number, written in decimal, represents an 8-bit octet (sometimes informally
referred to as a byte) giving each number a range of 0 through 255, inclusive.
When strung together, the four octets form the 32-bit IP address. Table 1 shows
32-bit values expressed as IP addresses. The largest possible value of a field
in dotted decimal notation is 255, which represents an octet where all the bits
IP Address Classes
IP addresses are generally
divided into different classes of addresses based on the number of hosts and subnetworks
required to support the hosts. As described in RFC 1166, IP addresses are 32-bit
quantities divided into five classes. Each class has a different number of bits
allocated to the network and host portions of the address. For this discussion,
consider a network to be a collection of computers (hosts) that have the same
network field values in their IP addresses. The concept of classes is being made
obsolete by classless interdomain routing (CIDR).
Instead of dividing
networks by class, CIDR groups them into address ranges. A network range consists
of an IP address prefix and a netmask length. The address prefix specifies the
high-order bits of the IP network address. The netmask length specifies the number
of high-order bits in the prefix that an IP address must match to fall within
the range indicated by the prefix.
For example, 192.168.42.x describes
a Class C network with addresses ranging from 192.168.42.0 through 192.168.42.255.
CIDR uses 192.168.42.0/24 to describe the same range of addresses. RIP version
1 is an example of a protocol that uses address classes. OSPF and BGP-4 are examples
of protocols that do not use address classes.
Table 1 - IP Address Notation
The class A IP address format allocates the highest 8 bits to
the network field and sets the highest-priority bit to 0 (zero). The remaining
24 bits form the host field. Only 126 class A networks can exist (0 is reserved,
and 127 is used for loopback networks), but each class A network can have almost
17 million hosts. No new class A networks can be assigned at this time.
address Host address
Class B Addresses
The class B IP address
format allocates the highest 16 bits to the network field and sets the two highest-order
bits to 1 and 0, providing a range from 128 through 191, inclusive. The remaining
16 bits form the host field. More than 16,000 class B networks can exist, and
each class B network can have up to 65,534 hosts.
address Host address
The class C IP address format allocates the highest 24 bits
to the network field and sets the three highest-order bits to 1, 1, and 0, providing
a range from 192 through 223, inclusive. The remaining 8 bits form the host field.
More than two million class C networks can exist, and each class C network can
have up to 254 hosts.
address Host address
Class D Addresses
class D IP address format was designed for multicast groups, as discussed in RFC
988. In class D addresses, the 4 highest-order bits are set to 1, 1, 1, and 0,
providing a range from 224 through 239, inclusive. Class D addresses are currently
used primarily for the multicast backbone (MBONE) of the Internet.
The class E IP address is reserved for future use. In class
E addresses, the 4 highest-order bits are set to 1, 1, 1, and 1. Routers currently
ignore class E IP addresses.
Reserved IP Addresses
IP addresses are reserved for special uses and cannot be used for host addresses.
Table 2 lists ranges of IP addresses and shows which addresses are reserved, which
are available to be assigned, and which are for broadcast.
networks on the local host|
| ||22.214.171.124 through 126.96.36.199||Available|
| ||188.8.131.52 through 184.108.40.206||Available|
through 220.127.116.11||Multicast group addresses|
Table 2 - Reserved and Available
Private IP Networks
RFC 1597 reserves
three IP network addresses for private networks. The addresses 10.0.0.0/8, 192.168.0.0/16,
and 172.16.0.0/20 can be used by anyone for setting up their own internal IP networks.
IP Address Conventions
If the bits in the host
portion of an address are all 0, that address refers to the network specified
in the network portion of the address. For example, the class C address 18.104.22.168
refers to a particular network. Historically, this address was used as a broadcast.
The standard for broadcast is high, which uses all 1s in the host portion
(for example, 192.168.1.255); however, many networks still use all 0s. The ImageStream
router can be configured either way and should be set to match the other systems
on your network. Note: Do not assign an IP address with all 0s or all 1s in the
host portion of the address to a host on the network, because these are reserved
as broadcast addresses. With CIDR, networks are specified with an IP prefix and
netmask length--for example, 172.16.0.0/16, 192.168.1.0/24, or 192.168.200.240/28.
A netmask is a four-octet number that
identifies either a supernetwork (supernet) or a subnetwork (subnet). A netmask
that designates a subnet is called a subnet mask.
Subnet Masks to Create IP Subnets
Subnet masks are used to divide networks
into smaller, more manageable groups of hosts known as subnets. Subnetting is
a scheme for imposing a hierarchy on hosts on a single physical network. The usual
practice is to use the first few bits in the host portion of the network address
for a subnet field. RFC 950, Internet Standard Subnetting Procedure, describes
A subnet mask identifies the subnet field of a network address.
This mask is a 32-bit number written in dotted decimal notation with all 1s (ones)
in the network and subnet portions of the address, and all 0s (zeros) in the host
portion. This scheme allows for the identification of the host portion of any
address on the network. Table 3 shows the subnet masks you can use to divide a
class C network into subnets.
|Length (Subnet Bits)||Number
of Subnets||Number of Hosts per Subnet||Hexadecimal
Subnet Mask||Dotted Decimal Subnet Mask|
Table 3 - Subnet Masks for a Class