Booting across the Network

Booting across the Network

At the heart of the operation of diskless workstations is the bootp protocol. The bootp protocol is a DARPA standard protocol supported on all Silicon Graphics servers and workstations. One of the devices that the Command Monitor can use for booting is the network. Silicon Graphics provides a TCP/IP boot protocol that lets you boot files that reside on another host in the network, if the other host supports the booting protocol. The network booting protocol is the bootp protocol. It is a datagram protocol that uses the User Datagram Protocol (UDP) of TCP/IP to transfer files across the Ethernet network.

To boot across the network, you must first determine the Internet address of the machine you want to boot. The Internet address is a number assigned by the network administrator of the network to which the system is attached. The format of the number is four decimal numbers between 0 and 255, separated by periods; for example:

192.20.0.2

Use the setenv command to set the netaddr environment variable to this address; for example:

setenv netaddr 192.20.0.2

Booting across the Network with bootp

Once you have set the netaddr environment variable, you can use bootp to refer to a remote file by using a file name of the form:

bootp()[hostname:] path

hostname is the name of the host where the file resides. The specified host must run the bootp server daemon, bootp. If you omit hostname, bootp broadcasts to get the file from any of the hosts on the same network as the machine making the request. The first host that answers fills the request. Only hosts that support bootp can respond to the request. It is safe to omit the hostname only when you know that the path is unique to a particular host, or when you know that all the copies of the file are interchangeable.
hostname can be the name of a host on a different Ethernet network from the machine that you are booting, if a gateway on the local Ethernet network provides a route to the remote host. The gateway must be an IRIS workstation running a bootp server that you have configured to do cross-network forwarding.

For more information about booting through gateways, see bootp(1M). For more information about the /etc/inetd.conf configuration file, see inetd(1M).
path is the pathname of a file on the remote host. For example, this command:
boot -f bootp()wheeler:/usr/local/boot/unix
boots the file /usr/local/boot/unix from the remote host wheeler. The command:

boot -f bootp()/usr/alice/help
boots the file /usr/alice/help from any host on the network responding to the bootp broadcast request that has a file of that name.

To configure the gateway to permit cross-network forwarding, follow these steps:

Log in as root or become the superuser by issuing the su command.
Edit the file /etc/inetd.conf on the gateway machine. This file configures the bootp server, which is started by the inetd(1M) daemon.
Change the bootp description so that inetd invokes bootp with the -f flag. Find this line:
bootp dgram udp wait root /usr/etc/bootp bootp
Add the -f flag to the final bootp on the line:

bootp dgram udp wait root /usr/etc/bootp bootp -f
Change the tftp configuration line in one of the following ways:
Remove the -s flag from the argument list for tftpd:

tftp dgram udp wait guest /usr/etc/tftpd tftpd -s
This allows tftpd access to all publicly readable directories. If you are concerned about a possible security compromise, you can instead explicitly list the directories to which tftpd needs access. In this case, you need to add /usr/etc:

tftp dgram udp wait guest /usr/etc/tftpd tftpd -s /usr/etc
See tftpd(1M) and tftp(1C) for more information.
Signal inetd to re-read its configuration file.
killall -1 inetd

Booting Across A Larger Network

If you have access to a larger network, and the bootable file you need is sufficiently remote on the network that the tftp and bootp timeouts and network delays are keeping you from booting successfully, it is possible to use an intermediary host as a bootp server.

As an example, consider the following situation. You have a host named local_host that needs to boot a kernel found on the remote system far_host. But the network is heavily used, resulting in bootp and tftp timing out before the boot operation can take place. However, a third host, near_host, has the optional NFS software and has automount(1M) running, allowing access to the files on far_host. To boot through this method, perform the following steps:

On near_host, the system acting as intermediary, log in as root and edit the file /etc/inetd.conf. This file configures the bootp server, which is started by the inetd(1M) daemon.
On near_host, change the bootp description in the /etc/inetd.conf file so that inetd invokes bootp with the -f flag. Find this line:
bootp dgram udp wait root /usr/etc/bootp bootp
Add the -f flag to the final bootp on the line:

bootp dgram udp wait root /usr/etc/bootp bootp -f
On near_host, change the tftp configuration line in the /etc/inetd.conf file in one of the following two ways:
Remove the -s /usr/local/boot string from the argument list for tftpd, so that the entry matches the following:

tftp dgram udp wait guest /usr/etc/tftpd tftpd
This allows tftpd access to all publicly readable directories.

If you are concerned about a possible security compromise, you can instead explicitly list the directories to which tftpd needs access. In this case, you need to add /hosts:

tftp dgram udp wait guest /usr/etc/tftpd tftpd -s /hosts
See tftpd(1M) and tftp(1C) for more information.
Signal inetd to re-read its configuration file.
killall -1 inetd
On far_host, the system on the distant subnetwork, use NFS to export the directory containing the needed bootable kernel (in this case, the file is /usr/local/boot/unix). If you need help exporting a directory, see the export(1M) reference page.
On local_host, the system you are trying to boot, give the command:
boot -f bootp()near_host:/hosts/far_host/usr/local/boot/unix
If bootp times out, try the command again, as automount may require a bit of time to retrieve the files from the remote system.