Directly mapping the numbers starting from 1 facilitates the writing of custom system utilities, diagnostic tools, and other short programs usually implemented as shell scripts. If you plan on having more than 9 nodes in your system, it might be desirable to name all of your nodes using 2 digits. For example, b1 becomes b01 and b2 becomes b02. Similarly, for systems with more than 99 nodes, b1 should become b001 and b10 should become b010.
When physically administrating a cluster, it is often necessary to know the MAC addresses of the network cards in nodes, as well as their names and IP addresses. The simplest reason is that when something goes wrong with a node you have to walk into the machine room and diagnose the problem, often simply rebooting the culprit node. For this reason, it is recommended that you label each node with its hostname, IP address, and the MAC addresses of the network interface cards. If you use a consistent IP address to hostname mapping, you can get by with just labeling the nodes with their names and MAC addresses. MAC addresses go in the bootptab (see Section 6.3.3), so you will want to record them when you install the NICs into their cases. If you forgot to do this, the ifconfig command will report the MAC address of configured controllers. For small systems labelling of nodes is largely superfluous, but for larger numbers of nodes, this simple measure could save you many hours.
6.2.1 Dynamically Assigned Addresses
So far we have discussed naming nodes with statically assigned addresses. Every time a node is booted, it obtains its hostname and IP address from its local configuration files. It is not always necessary to configure your system this way. If all of your internal nodes have identical software images, there is no reason why they necessarily require fixed IP addresses and hostnames. It is possible to configure a system so that every time an internal node boots, it receives an IP address from a pool of available addresses. Worldly nodes need to continue using fixed IP addresses because they provide resources to internal nodes that must be accessed through a known host address. The advantage of using dynamically assigned addresses is that internal nodes become completely interchangeable, facilitating certain system maintenance procedures. If you decide to convert your universally accessible machine to a guarded Beowulf, all you have to do is change the IP addresses in the DHCP or BOOTP server's configuration files, rather than update config files on every single node. The downside of dynamic addressing is that unless you take proper precautions it can become difficult to determine what physical box in the machine room corresponds to a specific name. This is where the suggested labeling of nodes with MAC addresses described above comes in handy. If you know the
