WANCHO@SIMTEL20.ARMY.MIL ("Frank J. Wancho") (09/01/88)
Monday evening SIMTEL20 came back online after being down for 18 days awaiting air conditioner repair. During the downtime, we activated duplicate logins on our sister site in St. Louis. However, unless our users happened to call in or paid attention to previous announcements to check the signon banner at the St. Louis host, they had no way of knowing to try the alternate host. That was one problem - admittedly one of having our users know our SOP. The other problem was that some, possibly critical or time-critical mail was eventually returned to the sender during that interval. And, as far as I know, there is no "automatic" redirection possible. Or is there? What I have in mind is that, given that I could have made the St. Louis host think that its alias was SIMTEL20.ARMY.MIL (and the older SIMTEL20.ARPA) via a quick modification to the hosts tables, would it have been (and is it) possible to have gotten our PSN to redirect connection requests intended for our downed host to the St. Louis host for the duration of the downtime? If not, why not? For those of us who take the requirement for mandatory Continuity of Operations Plans (COOP) seriously, such a feature would close the gap and make it reasonable to implement when needed. Note: I am aware of the clever solution to this problem implemented at BRL, but I'm not prepared to move off the backbone at this time (due to our heavy traffic which would probably swamp most gateways) to take advantage of that route. --Frank
ado@VAX.BBN.COM (Buz Owen) (09/02/88)
I believe you could use 1822L logical addressing for this purpose, by arranging that only one host enables a particular logical address at a time -- i.e. when backing up some other host. Of coure you have to using 1822l headers, and be willing to change your host addresses, both possibly formidable obstacles. Buz
craig@SH.CS.NET (Craig Partridge) (09/02/88)
> The other problem was that some, possibly critical or time-critical > mail was eventually returned to the sender during that interval. And, > as far as I know, there is no "automatic" redirection possible. Or is > there? Frank: Automatic redirection is possible using MX RR's in the domain name system. The feature was included for just this problem. Quite simply, you make your backup host a backup mail exchanger (MX). Then whenever your primary host is down, mail gets delivered to your backup. For short term outages, your backup machine simply waits for your primary to come up again, then forwards the mail on. But when the primary is going to be down for a long time, you can reconfigure your mailer to have the backup actually deliver the mail sitting in its queues. Craig
WANCHO@SIMTEL20.ARMY.MIL ("Frank J. Wancho") (09/02/88)
Bob, Most of our users exchange mail with other MILNET hosts. I suspect about 95-99% of those hosts still run off of the NIC hosts table, as we currently do. When we are all forced to use domain resolvers, then your suggested solution would appear the way to go. --Frank
mckee@MITRE.ARPA (H. Craig McKee) (09/02/88)
I am one of the (probably many) people who agree with the need for a COOP. It is my imperfect understanding that the PSNs can, or will, support logical adressing. Specifically, two or more PSN ports can have the same name, or, a single port can have two or more names. Such a capability would have made things easy for you. Regards - Craig
stjohns@BEAST.DDN.MIL (Mike St. Johns) (09/02/88)
Date: Thu, 01 Sep 88 16:02:24 -0400 From: Buz Owen <ado@VAX.BBN.COM> I believe you could use 1822L logical addressing for this purpose, by arranging that only one host enables a particular logical address at a time -- i.e. when backing up some other host. Of coure you have to using 1822l headers, and be willing to change your host addresses, both possibly formidable obstacles. Buz NO! NO! NO! If *everyone* on the Milnet had a capability for logical addressing, and a defined mapping between an IP address and a logical address, this would work. However, we've still got a substantial community of subscribers who use 1822; those who use X.25 have both the capability and the defined mappings. Eventually, we hope to modify the 1822 interface to conform to the 1822L bit mappings and to allow a vanilla 1822 host to specify a logical address without having to change its programming. That's a ways in the future - lots of other things have priority. Mike
brescia@PARK-STREET.BBN.COM (Mike Brescia) (09/02/88)
... SIMTEL20 came back online after being down for 18 days ... activated
duplicate logins on our sister site ...
Logical addressing is what you might use to direct connections to an alternate
server.
1. Since tac connections are probably still done numerically by your users,
you could educate them about opening connections by name if the name server
version of TACACS is running.
2. For long-term (more than a week) outage, you could try changing your host
table entry at your domain name server (or the NIC). Even hosts that use the
NIC host table should eventually get the address change.
3. On an arpanet (e.g. the Milnet), the PSN's support logical addressing,
both for X.25 and for 1822-AHIP. Your name server and host tables identify
your address as a 'logical' one, such as 26.64.0.99, and you then can tell
any one (or more) of your hosts to come up with that address. The problem
with this solution is that there are no hosts that implement 1822-AHIP
logical addressing.
4. If you were on an ethernet, you'd get logical addressing for free, and
your host would have to act as multiple addresses on a single interface.
... the clever solution to this problem implemented at BRL ...
Was this using ethernet addressing?
Yours for logical networking,
Mike