17.5. Protocol filtering

If you have a large volume of non-IP traffic on your network, isolating it from your NFS and NIS traffic may improve overall system performance by reducing the load on your network and servers. You can determine the relative percentages of IP and non-IP packets on your network using a LAN analyzer or a traffic filtering program. The best way to isolate your NFS and NIS network from non-IP traffic is to install a switch, bridge, or other device that performs selective filtering based on protocol. Any packet that does not meet the selection criteria is not forwarded across the device.

Devices that monitor traffic at the IP protocol level, such as routers, filter any non-IP traffic, such as IPX and DECnet packets. If two segments of a local area network must exchange IP and non-IP traffic, a switch, bridge, or router capable of selective forwarding must be installed. The converse is also an important network planning factor: to insulate a network using only TCP/IP-based protocols from volumes of irrelevant traffic -- IPX packets generated by a PC network, for example -- a routing device filtering at the IP level is the simplest solution.

Partitioning a network and increasing the available bandwidth should ease the constraints imposed by the network, and spur an increase in NFS performance. However, the network itself is not always the sole or primary cause of poor performance. Server- and client-side tuning should be performed in concert with changes in network topology. Chapter 16, "Server-Side Performance Tuning" has already covered server-side tuning; Section 18.1, "Slow server compensation" will cover the client-side tuning issues.

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