Addresses, Protocols, and Ports

This chapter provides a quick reference for IP addresses, protocols, and applications.

• IPv4 Addresses and Subnet Masks, on page 1

• IPv6 Addresses, on page 5

• Protocols and Applications, on page 10

• TCP and UDP Ports, on page 11

• Local Ports and Protocols, on page 15

• ICMP Types, on page 16

IPv4 Addresses and Subnet Masks

Classes

IP host addresses are divided into three different address classes: Class A, Class B, and Class C. Each class

fixes the boundary between the network prefix and the host number at a different point within the 32-bit

address. Class D addresses are reserved for multicast IP.

• Class A addresses (1.xxx.xxx.xxx through 126.xxx.xxx.xxx) use only the first octet as the network prefix.

• Class B addresses (128.0.xxx.xxx through 191.255.xxx.xxx) use the first two octets as the network prefix.

• Class C addresses (192.0.0.xxx through 223.255.255.xxx) use the first three octets as the network prefix.

Because Class A addresses have 16,777,214 host addresses, and Class B addresses 65,534 hosts, you can use

subnet masking to break these huge networks into smaller subnets.

Addresses, Protocols, and Ports

• 172.16.0.0 through 172.31.255.255

• 192.168.0.0 through 192.168.255.255

Subnet Masks

A subnet mask lets you convert a single Class A, B, or C network into multiple networks. With a subnet mask,

you can create an extended network prefix that adds bits from the host number to the network prefix. For

example, a Class C network prefix always consists of the first three octets of the IP address. But a Class C

extended network prefix uses part of the fourth octet as well.

Subnet masking is easy to understand if you use binary notation instead of dotted decimal. The bits in the

subnet mask have a one-to-one correspondence with the Internet address:

• The bits are set to 1 if the corresponding bit in the IP address is part of the extended network prefix.

specify a subnet mask like 11111111.11111111.11111000.00000000, which uses only 5 bits of the third octet

for the extended network prefix.

You can write a subnet mask as a dotted-decimal mask or as a /bits (“slash bits”) mask. In Example 1, for a

dotted-decimal mask, you convert each binary octet into a decimal number: 255.255.255.0. For a /bits mask,

you add the number of 1s: /24. In Example 2, the decimal number is 255.255.248.0 and the /bits is /21.

You can also supernet multiple Class C networks into a larger network by using part of the third octet for the

extended network prefix. For example, 192.168.0.0/20.

See the following table to determine the subnet mask based on how many hosts you want.

The first and last number of a subnet are reserved, except for /32, which identifies a single host.

Addresses, Protocols, and Ports

The following sections describe how to determine the network address to use with a subnet mask for a Class

C-size and a Class B-size network.

For a network between 2 and 254 hosts, the fourth octet falls on a multiple of the number of host addresses,

starting with 0. For example, The following table shows the 8-host subnets (/29) of 192.168.0.x.

The first and last address of a subnet are reserved. In the first subnet example, you cannot use 192.168.0.0 or

192.168.0.7.

Addresses, Protocols, and Ports

192.168.0.8 to 192.168.0.15192.168.0.8

192.168.0.16 to 192.168.0.31192.168.0.16

——

192.168.0.248 to 192.168.0.255192.168.0.248

To determine the value of the third octet, follow these steps:

1. Calculate how many subnets you can make from the network by dividing 65,536 (the total number of

addresses using the third and fourth octet) by the number of host addresses you want.

For example, 65,536 divided by 4096 hosts equals 16. Therefore, there are 16 subnets of 4096 addresses

each in a Class B-size network.

2. Determine the multiple of the third octet value by dividing 256 (the number of values for the third octet)

by the number of subnets:

In this example, 256/16 = 16.

The third octet falls on a multiple of 16, starting with 0.

The following table shows the 16 subnets of the network 10.1.

10.1.16.0 to 10.1.31.25510.1.16.0

10.1.32.0 to 10.1.47.25510.1.32.0

——

10.1.240.0 to 10.1.255.25510.1.240.0

Addresses, Protocols, and Ports

IPv6 Addresses

IPv6 is the next generation of the Internet Protocol after IPv4. It provides an expanded address space, a

simplified header format, improved support for extensions and options, flow labeling capability, and

authentication and privacy capabilities. IPv6 is described in RFC 2460. The IPv6 addressing architecture is

described in RFC 3513.

This section describes the IPv6 address format and architecture.

You do not need to include the leading zeros in an individual field of the address, but each field must contain

at least one digit. So the example address 2001:0DB8:0000:0000:0008:0800:200C:417A can be shortened to

2001:0DB8:0:0:8:800:200C:417A by removing the leading zeros from the third through sixth fields from the

left. The fields that contained all zeros (the third and fourth fields from the left) were shortened to a single

zero. The fifth field from the left had the three leading zeros removed, leaving a single 8 in that field, and the

sixth field from the left had the one leading zero removed, leaving 800 in that field.

It is common for IPv6 addresses to contain several consecutive hexadecimal fields of zeros. You can use two

colons (::) to compress consecutive fields of zeros at the beginning, middle, or end of an IPv6 address (the

colons represent the successive hexadecimal fields of zeros). The following table shows several examples of

::0:0:0:0:0:0:0:0Unspecified

Two colons (::) can be used only once in an IPv6 address to represent successive fields of zeros.

Addresses, Protocols, and Ports

An alternative form of the IPv6 format is often used when dealing with an environment that contains both

IPv4 and IPv6 addresses. This alternative has the format x:x:x:x:x:x:y.y.y.y, where x represent the hexadecimal

values for the six high-order parts of the IPv6 address and y represent decimal values for the 32-bit IPv4 part

of the address (which takes the place of the remaining two 16-bit parts of the IPv6 address). For example, the

IPv4 address 192.168.1.1 could be represented as the IPv6 address 0:0:0:0:0:0:FFFF:192.168.1.1 or

::FFFF:192.168.1.1.

IPv6 Address Types

Addresses, Protocols, and Ports

A link-local address is an IPv6 unicast address that can be automatically configured on any interface using

the link-local prefix FE80::/10 and the interface identifier in modified EUI-64 format. Link-local addresses

Addresses, Protocols, and Ports

Addresses, Protocols, and Ports

• An anycast address cannot be used as the source address for an IPv6 packet.

• An anycast address cannot be assigned to an IPv6 host; it can only be assigned to an IPv6 router.

Anycast addresses are not supported on the ASA.

IPv6 hosts must, at a minimum, be configured with the following addresses (either automatically or manually):

• A link-local address for each interface

• The loopback address

• The All-Nodes multicast addresses

• A Solicited-Node multicast address for each unicast or anycast address

Addresses, Protocols, and Ports

Addresses, Protocols, and Ports