• Optimize bandwidth usage on WAN links to improve performance
• Optimize bandwidth usage on WAN links to save money
• Implement security policies
• Implement policies regarding some traffic having priority over other traffic
• Scale internetworks to a large size and retain good performance

Attaining these goals can be difficult, but it can also be assisted by making use of particular software features in routers and other network devices.  The following sections in this page give a very quick survey of  the following.

• Access lists
• Encryption
• Proxy services
• Compression
• Traffic shaping
• Queueing
• Prioritizing
• RSVP
• Tag Switching

Access Lists.  Access Lists provide a number of capabilities such as

• control whether network traffic is forwarded or blocked at router interfaces
• provide a basic level of security
• control the traffic volume to improve performance

When configuring access lists you provide a set of criteria that will be applied to each packet that is processed by the router.  The router decides whether to forward or block each packet based on how the packet matches up with access list criteria.

Standard access lists allow only simple criteria to be specified, such as packet source address.  Extended access lists allow additional, more complex criteria to be specified, such as destination address, upper layer protocol, and application port number.  Each criterion is specified in a separate statement.

There are many other important issues to consider when using access lists such as list order, applying lists to inbound or outbound interfaces, numbering the lists and wildcard masks.  One also needs to consider the impact that access lists have on overall router performance.

Encryption Options.  It is often very important to encrypt data that is being sent across internetworks to help ensure it is accessed only by authorized users.  There are many different ways to encrypt data and Cisco has its own options.

This is a topic better left to the security course that follows this semester.

Proxy Services.  Some of the main features that can be provided by proxy services are

• Resource discovery on serverless LANs
• Traffic reduction on bridged networks and LANs
• Improved performance for time sensitive applications

Compression Services.  The basic function of data compression is to reduce the size of a frame of data to be transmitted over a network link.  Data compression algorithms use two types of encoding techniques

• Statistical
  • uses a fixed, usually non-adaptive, coding method is best used for single applications with relatively consistent and predictable data.  Therefore these are not usually all that useful with routers.
• Dictionary
  • after data is encoded it is stored in memory in a dictionary style list.

Traffic Shaping.  Generally, traffic shaping can reduce outbound and inbound traffic from particular sources or going to particular destinations.  It helps enable network administrators to impact what traffic is allowed on the internal network.

Queueing Services.  By queueing, network administrators are better able to manage varying demands on networks and routers.  Different things waiting can be prioritized in a large variety of ways.

RSVP.  RSVP has been designed to allow routers to communicate among themselves and with end systems so that they can reserve end-to-end network resources for applications that cannot tolerate fluctuations in bandwidth or time delays.