kannan@manhandler.oar.net (Kannan Varadhan) (08/07/90)
We are trying to represent a multi-homed machine in a zone file as a machine having multiple A records. We'd like to be aware of the implications this might have on different application programs like telnet and ftp. My understanding is that sendmail, if it detects multiple MXs of equal weight, picks up one RR at random, and pops the mail over to that machine. Is there some such load-balancing feature built onto telnet, ftp, mail transfer agents etc. when multiple A records for the same FQDN are seen? Or, do they pick up the first A record (call it the primary Address), try it, if it fails, then try the other addresses in the order specified in the zone file? Can we rely on named returning all the addresses for a given machine in the order specified? Does the answer depend on the version of telnet, ftp, mail transport agent, named etc. one uses? The reasoning is that we'd like not to have any load-balancing built in. We'd like users to try the primary address. If that fails for some reasons in the underlying network, we'd like the application to then try the secondary addresse(es) until all of the addresses have been exhaustively tried. For the record, the named that will answer for the multiple A records will be BIND 4.8.2, the one with the UofToronto mods. At this point, I cannot say much about the versions of other application software out there in the void, but I suspect a little of everything. Any pointers on which RFCs to look at would be appreciated too, Please mail me the answers....I'll summarise the replies within a week. I would actually be trying some of this by experimentation too, so I'll post whatever I find to the tcp-ip list, Kannan