Managing NFS and NIS, 2nd Edition - Mike Eisler [255]
Heavily used NFS servers will benefit from their own "fast" branch, but try to keep NFS clients and servers logically close in the network topology. Try to minimize the number of switches and routers that traffic must cross. A good rule of thumb is to try to keep 80% of the traffic within the network and only 20% of the traffic from accessing the backbone.
ATM and FDDI networks
ATM (Asynchronous Transfer Mode) and FDDI (Fiber Distributed Data Interface) networks are two other forms of high-bandwidth networks that can sustain multiple high-speed concurrent data exchanges with minimal degradation. ATM and FDDI are somewhat more efficient than Fast Ethernet in data-intensive environments because they use a larger MTU (Maximum Transfer Unit), therefore requiring less packets than Fast Ethernet to transmit the same amount of information. Note that this does not necessarily present an advantage to attribute-intensive environments where the requests are small and always fit in a Fast Ethernet packet.
Although ATM promises scalable and seamless bandwidth, guaranteed QoS (Quality of Service), integrated services (voice, video, and data), and virtual networking, Ethernet technologies are not likely to be displaced. Today, ATM has not been widely deployed outside backbone networks. Many network administrators prefer to deploy Fast Ethernet and Gigabit Ethernet because of their familiarity with the protocol, and because it requires no changes to the packet format. This means that existing analysis and network management tools and software that operate at the network and transport layers, and higher, continue to work as before. It is unlikely that ATM will experience a significant amount of deployment outside the backbone.
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[1] When BIND's round-robin feature is enabled, the order of the server's addresses returned is shifted on each query to the name server. This allows a different address to be used by each client's request.
Impact of partitioning
Although partitioning is a solution to many network problems, it's not entirely transparent. When you partition a network, you must think about the effect of partitioning on NIS, and the locations of diskless nodes and their boot servers.
NIS in a partitioned network
NIS is a point-to-point protocol once a server binding has been established. However, when ypbind searches for a server, it broadcasts an RPC request. Switches and bridges do not affect ypbind, because switches and bridges forward broadcast packets to the other physical network. Routers don't forward broadcast packets to other IP networks, so you must make configuration exceptions if you have NIS clients but no NIS server on one side of a router.
It is not uncommon to attach multiple clients to a hub, and multiple hubs to a switch. Each switch branch acts as its own segment in the same way that bridges create separate "collision domains." Unequal distribution of NIS servers on opposite sides of a switch branch (or bridge) can lead to server victimization. The typical bridge adds a small delay to the transit time of each packet, so ypbind requests will almost always be answered by a server on the client's side of the switch branch or bridge. The relative delays in NIS server response time are shown in Figure 17-2.
Figure 17-2. Bridge effects on NIS
If there is only one server on bridge network A, but several on bridge network B, then the "A" network server handles all NIS requests on its network segment until it becomes so heavily loaded that servers on the "B" network reply to ypbind faster, including the bridge-related packet delay. An equitable distribution of NIS servers across switch branch (or bridge) boundaries eliminates this excessive loading problem.
Routers and gateways present a more serious problem for NIS. NIS servers and clients must be on the same IP network because a router or gateway will not forward the client's ypbind broadcast outside the local IP network. If there are no NIS servers on the "inside" of a router, use ypinit at configuration time as discussed in Section