RFC 974 - Mail Routing and the Domain System
Hello, 'Just want to clarify something... is there a difference between: domain.com. MX 10 mx1.domain.com. domain.com. MX 10 mx2.domain.com. domain.com. MX 10 mx3.domain.com. ;... mx1.domain.com. IN A 10.0.0.1 mx2.domain.com. IN A 10.0.0.2 mx3.domain.com. IN A 10.0.0.3 and: domain.com. MX 10 mx.domain.com. ;... mx.domain.com. IN A 10.0.0.1 mx.domain.com. IN A 10.0.0.2 mx.domain.com. IN A 10.0.0.3
From RFC 974:
"...Note that multiple MXs may have the same preference value. In this case, all MXs at with a given value must be tried before any of a higher value are tried..." Is the behaviour the same with the round-robined configuration? Thanks in advance, Mike _________________________________________________________ DO YOU YAHOO!? Get your free @yahoo.com address at http://mail.yahoo.com
Michael J. Maravillo wrote:
Hello,
'Just want to clarify something... is there a difference between:
domain.com. MX 10 mx1.domain.com. domain.com. MX 10 mx2.domain.com. domain.com. MX 10 mx3.domain.com. ;... mx1.domain.com. IN A 10.0.0.1 mx2.domain.com. IN A 10.0.0.2 mx3.domain.com. IN A 10.0.0.3
and:
domain.com. MX 10 mx.domain.com. ;... mx.domain.com. IN A 10.0.0.1 mx.domain.com. IN A 10.0.0.2 mx.domain.com. IN A 10.0.0.3
From RFC 974:
"...Note that multiple MXs may have the same preference value. In this case, all MXs at with a given value must be tried before any of a higher value are tried..."
Is the behaviour the same with the round-robined configuration?
My imperfect understanding of how most mail agents handle MX records is that with the first configuration, mx1 will always be tried first, followed by mx2, etc. With the second configuration, a BIND server will return the A addresses in an effectively random pattern, so load should be distributed across the 3 servers. For future reference you are better off asking at bind-users@vix.com, which seems to be back up and running. Good luck, Doug -- *** Chief Operations Officer, DALnet IRC network *** "Yes, the president should resign. He has lied to the American people, time and time again, and betrayed their trust. He is no longer an effective leader. Since he has admitted guilt, there is no reason to put the American people through an impeachment. He will serve absolutely no purpose in finishing out his term; the only possible solution is for the president to save some dignity and resign." - William Jefferson Clinton, 1974
My imperfect understanding of how most mail agents handle MX records is that with the first configuration, mx1 will always be tried first, followed by mx2, etc. With the second configuration, a BIND server will return the A addresses in an effectively random pattern, so load should be distributed across the 3 servers.
Indeed if the MXes have different priorities, only in this case they have the same priorities so they will also be load balanced. (The key being, BIND will round robin any kind of record, not just A records). I tried to answer this question earlier but couldn't come up with a good answer so I kept quiet :-( -Phil
Phillip Vandry wrote:
My imperfect understanding of how most mail agents handle MX records is that with the first configuration, mx1 will always be tried first, followed by mx2, etc. With the second configuration, a BIND server will return the A addresses in an effectively random pattern, so load should be distributed across the 3 servers.
Indeed if the MXes have different priorities, only in this case they have the same priorities so they will also be load balanced. (The key being, BIND will round robin any kind of record, not just A records).
BIND will round robin the MX records, how mail agents deal with multiple MX records of the same priority is less of a known factor (to me at least). Actually I'd be interested to hear from people who try both configurations for say a month at a time to see what influence each configuration has if any. Doug -- *** Chief Operations Officer, DALnet IRC network *** "Yes, the president should resign. He has lied to the American people, time and time again, and betrayed their trust. He is no longer an effective leader. Since he has admitted guilt, there is no reason to put the American people through an impeachment. He will serve absolutely no purpose in finishing out his term; the only possible solution is for the president to save some dignity and resign." - William Jefferson Clinton, 1974
Studded wrote:
BIND will round robin the MX records, how mail agents deal with multiple MX records of the same priority is less of a known factor (to me at least). Actually I'd be interested to hear from people who try both configurations for say a month at a time to see what influence each configuration has if any.
I was just looking at this code in sendmail the other day. sendmail will randomize when it gets multiple MX records of the same priority. Look at mxrand() in domain.c. -- Michael L. Barrow * <mlbarrow@eni.net> * Network Engineer Epoch Internet * DSL Engineering * (949) 399-8413
On Tue, 15 Sep 1998, Studded wrote:
Michael J. Maravillo wrote:
domain.com. MX 10 mx1.domain.com. domain.com. MX 10 mx2.domain.com. domain.com. MX 10 mx3.domain.com. ;... mx1.domain.com. IN A 10.0.0.1 mx2.domain.com. IN A 10.0.0.2 mx3.domain.com. IN A 10.0.0.3
and:
domain.com. MX 10 mx.domain.com. ;... mx.domain.com. IN A 10.0.0.1 mx.domain.com. IN A 10.0.0.2 mx.domain.com. IN A 10.0.0.3
From RFC 974:
"...Note that multiple MXs may have the same preference value. In this case, all MXs at with a given value must be tried before any of a higher value are tried..."
Is the behaviour the same with the round-robined configuration?
My imperfect understanding of how most mail agents handle MX records is that with the first configuration, mx1 will always be tried first, followed by mx2, etc. With the second configuration, a BIND server will return the A addresses in an effectively random pattern, so load should be distributed across the 3 servers.
For future reference you are better off asking at bind-users@vix.com, which seems to be back up and running.
One small detail that you seem to have left out. If you use solution number 2 I believe the following will happen. Assuming for whatever reason 10.0.0.2 goes down. SMTP1 attempts to send mail to domain.com Domain.com's DNS server says that all mail goes to mx.domain.com and says that mx.domain.com points to 10.0.0.2. At this point, SMTP1 can not send any mail to domain.com until cached zone for domain.com expires on SMTP1 at which point, SMTP1 will requery ns.domain.com and may or may not get a different address for mx.domain.com I'm not sure as to the first scenario, but I believe from my own experience sending mail to domains with multiple mail handlers (ie mx1.domain.com mx2.domain.com etc.) that it will send to different servers each time it hits them. Once again, I do NOT know this to be true, this is just what I seem to have experienced. Also, I think this type of thing would be better posted on list@inet-access.net not a bind list since it relates to Sendmail operation as well as bind.. Tim ---------------------------------------------------- Timothy M. Wolfe | Why surf when you can Sail? tim@clipper.net | Join Oregon's Premier Sr. Network Engineer | Wireless Internet Provider! ClipperNet Corporation | http://www.clipper.net/ ----------------------------------------------------
participants (5)
-
Michael J. Maravillo -
Michael L. Barrow -
Phillip Vandry -
Studded -
Tim Wolfe