ACLs should be defined on
a per-protocol and per source/destination/port basis to achieve more granularity and control on various types of
traffic.
To better understand the use of ACLs, the next sections provide an overview of basic IP addressing, subnets and
masks, and IP classes.
IP Address Overview
The IP address is the address assigned to a particular network and the host within the network.
There are two basic types of IP addresses:
IP Version 4 (IPv4): IPv4 was initially deployed in January 1983 and is commonly used in today's
networks in general deployment. IPv4 addresses are 32-bit numbers displayed as four octets in dotted
decimal notation (for example, 10.1.1.1). RFC 1166 specifies the IPv4 address format.
IP Version 6 (IPv6) or IPng: IPv6, also known as IPng, is a next-generation Internet protocol, with a
new version designed to be an evolutionary move in Internet addressing. Growth is the basic issue
because the IPv4 address is becoming increasingly strained. This scarce has laid the foundation for the
next generation IP. IPv6 addresses are 128-bit numbers and are typically displayed in hexadecimal strings
(for example, 2080:0:0:2:8:400:20AC:217B). Cisco Systems announced IPv6 support in Cisco IOS
12.
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