Managing NFS and NIS, 2nd Edition - Mike Eisler [256]
Effects on diskless nodes
Diskless nodes should be kept on the same logical network as their servers unless tight constraints require their separation. If a router is placed between a diskless client and its server, every disk operation on the client, including swap device operations, has to go through the router. The volume of traffic generated by a diskless client is usually much larger — sometimes twice as much — than that of an NFS client getting user files from a server, so it greatly reduces the load on the router if clients and servers are kept on the same side of the router.[2]
Booting a client through a router is less than ideal, since the diskless client's root and swap partition traffic unnecessarily load the packet forwarding bandwidth of the router. However, if necessary, a diskless client can be booted through a router as follows:
Some machine on the client's local network must be able to answer Reverse ARP (RARP) requests from the machine. This can be accomplished by publishing an ARP entry for the client and running in.rarpd on some host on the same network:in.rarpd hme 0
In Solaris, in.rarpd takes the network device name and the instance number as arguments. In this example we start in.rarpd on /dev/hme0, the network interface attached to the diskless client's network. in.rarpd uses the ethers, hosts, and ipnodes databases[3] to map the requested Ethernet address into the corresponding IP address. The IP address is then returned to the diskless client in a RARP reply message. The diskless client must be listed in both databases for in.rarpd to locate its IP address.
A host on the local network must be able to tftp the boot code to the client, so that it can start the boot sequence. This usually involves adding client information to /tftpboot on another diskless client server on the local network.
Once the client has loaded the boot code, it looks for boot parameters. Some server on the client's network must be able to answer the bootparams request for the client. This entails adding the client's root and swap partition information to the local bootparams file or NIS map. The machine that supplies the bootparam information may not have anything to do with actually booting the system, but it must give the diskless client enough information for it to reach its root and swap filesystem servers through IP routing. Therefore, if the proxy bootparam server has a default route defined, that route must point to the network with the client's NFS server on it.
If the NIS server is located across the router, the diskless client will need to be configured at installation time, or later on with the use of the ypinit command, in order to boot from the explicit NIS server. This is necessary because ypbind will be unable to find an NIS server in its subnetwork through a broadcast.
* * *
[2] Although not directly related to network topology, one of the best things you can do for your diskless clients is to load them with an adequate amount of memory so that they can perform aggressive caching and reduce the number of round trips to the server.
[3] The ethers database is stored in the local file /etc/ethers or the corresponding NIS map. The hosts and ipnodes database is located in the local files /etc/inet/hosts and /etc/inet/ipnodes, or DNS and NIS maps. The search order depends on the contents of the name switch configuration file /etc/nsswitch.conf.
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