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.