Depends on what you want to accomplish. Keep in mind the purpose of what
you're doing and what you're dealing with.
If you want to ensure that you have published mail handlers in a way that
those that want to communicate with you can understand with a goal of having
high availability, then you would want to identify the lowest common
denominator of client and appeal to that. 2821 may not be what you want.
821 might be a little more in line with what you're trying to accomplish.
Depends on what's out there trying to communicate with you and the
understanding that client has of your mail handlers.
Using MX records of equal weight would give you pretty good results in most
situations. You may want to prioritize differently if you had several mail
handlers of different capabilities. For example, if you had a MTA that was
on a lower class of hardware (and therefore couldn't handle the same volume)
you might want it to be there as a last resort handler. Your other two
MTA's are the same and similarly connected so you would prioritize them the
same (most likely).
In your case, I'd use multiple MX records and I would weight the same since
you only have two. As long as when a failure occurs it's enough to trigger
the sending MTA to try other records you'll not interrupt mail flow.
Additionally, since SMTP is a store and forward protocol, you won't
interrupt mail flow as long as you put the MTA back in service in a
reasonable amount of time (seems like some are using 24 hours as the amount
of time to queue mail so it seems reasonable to put the MTA back in service
w/in that time frame).
DNS RR's with a zero TTL are just plain rude when used for everyday usage,
but they can be useful when making changes on your network. I haven't read
that pdf yet, but should be interesting to see the context.
Al
From: Freddy HARTONO <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: [email protected]
Subject: RE: [ActiveDir] [Way OT] DNS MX load balancing questions...
Date: Sun, 11 Dec 2005 09:40:58 +0800
Hi Deji
Thanks for the replies
That means it makes no sense to invest in having 1 backup MX of lower
priorities?
So basically what I need is as below?
Mydomain MX 10 mail1.mydomain.com
MX 10 mail2.mydomain.com
MX 10 mail3.mydomain.com
Instead of
Mydomain MX 10 mail1.mydomain.com
MX 10 mail2.mydomain.com
MX 100 mail3.mydomain.com?
Since with all 3 of the same priorities, if any of the mail is down (mail2)
for example, it will retry to mail1 and mail3 automatically according to
RFC?
Do you happen to have the KB of the exchange issue mentioned below, just
wanted to readup on that bug somehow :)
Basically we're trying to purchase spam/virus gateways in front of
exchange,
and I had the idea that it needs to be 3 appliances (2 for load balancing,
1
for backup).
Thank you and have a splendid day!
Kind Regards,
Freddy Hartono
Group Support Engineer
InternationalSOS Pte Ltd
mail: [EMAIL PROTECTED]
phone: (+65) 6330-9785
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
[EMAIL PROTECTED]
Sent: Sunday, December 11, 2005 12:31 AM
To: [email protected]
Subject: RE: [ActiveDir] [Way OT] DNS MX load balancing questions...
>>> RFC 2821 requires a mail server to choose MX records randomly when
>>> the
records are the same priority, but to try all if the initial one chosen
doesn't work (until it finds one that does work or the pool is exhausted).
Correct. There was, however, an issue early this year (or was it late last
year?) where 2K3 SMTP servers were failing to fail over to the next
available SMTP servers on the list they receive from a target DNS server. I
think this was corrected with a hotfix, but the issue will still exist in a
gold, un-hotfixed version.
>>>The above means it will try MX of other priorities right (not the
>>>other of
the same priorities correct?) - sorry just not having a clear word by word
answer in the RFC document itself.
It will continue to use the highest one, until that one stops responding.
As
long as the highest-prioritized one continues to accept emails, the
originating server will have no need to try another one.
HTH
Sincerely,
Dèjì Akómöláfé, MCSE+M MCSA+M MCT
Microsoft MVP - Directory Services
www.readymaids.com - we know IT
www.akomolafe.com
Do you now realize that Today is the Tomorrow you were worried about
Yesterday? -anon
________________________________
From: [EMAIL PROTECTED] on behalf of Freddy HARTONO
Sent: Sat 12/10/2005 7:07 AM
To: [email protected]
Subject: RE: [ActiveDir] [Way OT] DNS MX load balancing questions...
Hi Michael
Thanks for the quick reply.
RFC 2821 requires a mail server to choose MX records randomly when the
records are the same priority, but to try all if the initial one chosen
doesn't work (until it finds one that does work or the pool is exhausted).
The above means it will try MX of other priorities right (not the other of
the same priorities correct?) - sorry just not having a clear word by word
answer in the RFC document itself.
One of my vendor is giving me a whitepaper from barracuda appliance that
explains how its done, but mentioned that with MX listing below it will
provides load balancing AND redundancy (crap to me but now im getting
confused myself)
http://www.barracudanetworks.com/ns/downloads/Barracuda_WP_MX_Load_Balancing
.
pdf
Is it recommended that the TTL for the domain be set to 0 when using this
MX
load balancing method?
Thank you and have a splendid day!
Kind Regards,
Freddy Hartono
Group Support Engineer
InternationalSOS Pte Ltd
mail: [EMAIL PROTECTED]
phone: (+65) 6330-9785
________________________________
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Michael B. Smith
Sent: Friday, December 09, 2005 8:52 PM
To: [email protected]
Subject: RE: [ActiveDir] [Way OT] DNS MX load balancing questions...
You should have two separate MX records
@ IN MX 10 mail1.mydomain.com.
@ IN MX 10 mail2.mydomain.com.
Mail1 IN A 10.1.1.1
Mail2 IN A 10.2.2.2
RFC 2821 requires a mail server to choose MX records randomly when the
records are the same priority, but to try all if the initial one chosen
doesn't work (until it finds one that does work or the pool is exhausted).
Your proposal below has the problem you describe.
________________________________
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Freddy HARTONO
Sent: Friday, December 09, 2005 7:43 AM
To: [email protected]
Subject: [ActiveDir] [Way OT] DNS MX load balancing questions...
Hi All
Was just trying to understand something and am getting conflicting
results..
If I set the following (or 2 mx of the same priority with 2 differnet a
records)
Mydomain.com MX 10 mail.mydomain.com
Mail.mydomain.com A 10.1.1.1
Mail.mydomain.com A 10.2.2.2
I understand that will provide dns roundrobin but what happened if I
shutdown 10.2.2.2, will I lose (logically) 50% of my mail as I do not have
another fallback MX??
My understanding is that it does so as the sender mail server will cache
the
MX record and A record and will only send to there, am I right or am I
getting this wrong?
If I'm shutting down 10.2.2.2, will the sender mail server retries to
10.1.1.1? (lets assume there's no ttl reconfig to zero)
Thanks lots
Thank you and have a splendid day!
Kind Regards,
Freddy Hartono
Group Support Engineer
InternationalSOS Pte Ltd
mail: [EMAIL PROTECTED]
phone: (+65) 6330-9785
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