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The standard SunOS ypbind(8) (and, until now, the FreeBSD ypbind) only selects servers based on whether or not they respond to clnt_broadcast(). Ypbind(8) broadcasts to the YPPROC_DOMAIN_NONACK procedure and waits for answers; whichever server answers first is the one ypbind uses for the local client binding. This mechanism fails when binding across subnets is desired. In order for a client on one subnet to bind to a server on another subnet, the gateway(s) between the client and server must be configured to forward broadcasts. If this is not possible, then a slave server must be installed on the remote subnet. If this is also not possible, you have to force the client to bind to the remote server with ypset(8). Unfortunately, this last option is less than ideal. If the remote server becomes unavailable, ypbind(8) will lose its binding and revert to its broadcast-based search behavior. Even if there are other servers available, or even if the original server comes back up, ypbind(8) will not be able to create a new binding since all the servers are on remote subnets where its broadcasts won't be heard. If the administrator isn't around to run ypset(8) again, the system is hosed. In some Linux NIS implementations, there exists a yp.conf file where you can explicitly specify a server address and avoid the use of ypbind altogether. This is not desireable since it removes the possibility of binding to an alternate server in the event that the one specified in yp.conf crashes. Some people have mentioned to me how they though the 'restricted mode' operation (using the -S flag) could be used as a solution for this problem since it allows one to specify a list of servers. In fact, this is not the case: the -S flag just tells ypbind(8) that when it listens for replies to its broadcasts, it should only honor them if the replying hosts appear in the specified restricted list. This behavior has now been changed. If you use the -m flag in conjunction with the -S flag, ypbind(8) will use a 'many-cast' instead of a broadcast for choosing a server. In many-cast mode, ypbind(8) will transmit directly to the YPPROC_DOMAIN_NONACK procedure of all the servers specified in the restricted mode list and then wait for a reply. As with the broadcast method, whichever server from the list answers first is used for the local binding. All other behavior is the same: ypbind(8) continues to ping its bound server every 60 seconds to insure it's still alive and will many-cast again if the server fails to respond. The code used to achieve this is in yp_ping.c; it includes a couple of modified RPC library routines. Note that it is not possible to use this mechanism without using the restricted list since we need to know the addresses of the available NIS servers ahead of time in order to transmit to them. Most-recently-requested by: Tom Samplonius |
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| Makefile | ||
| yp_ping.c | ||
| yp_ping.h | ||
| ypbind.8 | ||
| ypbind.c | ||