1.2 Overview of Scalable Internetworks
1.2.4 Making the network efficient
Optimizing your network at all layers of an internetwork hierarchy is critical because it can reduce potential costs in additional hardware or WAN services. In this semester, the focus is on optimizing your bandwidth. Bandwidth optimization is normally done by reducing the amount of update traffic on the LAN over a WAN connection, without dropping essential routing information.

Cisco IOS features that can help optimize bandwidth use include:

  • Access lists
  • Snapshot routing
  • Compression over WANs

Access Lists

Access lists can be used to permit or deny (drop) protocol update traffic, data traffic, and broadcast traffic. Access lists are available for IP, IPX, and AppleTalk and can be tailored to meet the needs for each protocol. An access list, for example, can be defined by Transmission Control Protocol (TCP) port or by IPX network number, depending on the situation.

Snapshot Routing

Snapshot routing allows peer routers to exchange full distance vector routing information upon initial connection, and then on a predefined interval. Typically used with ISDN, this feature can reduce WAN costs when using distance vector protocols because routing information is exchanged at an interval you define. Between update exchanges, the routing tables for the distance vector protocols are kept frozen. Snapshot routing is only for distance vector protocols such as IP RIP. If you are using link-state protocols, other options are available, such as OSPF for on-demand circuits. This feature is not discussed in this semester, but performs a function similar to snapshot routing.

Compression over WANs

Several compression techniques can be used to reduce traffic that is crossing a WAN connection. Cisco supports TCP/IP header compression and data (payload) compression. In addition, you can configure link compression, which compresses header and data information in packets that cross point-to-point (leased lines) connections. Compression is accomplished in software by the router before the frame is placed on the medium.