MX question

[Kevin Darcy]

Well, it *shouldn't* be. According to RFC 2821, mail servers should randomize
between MX targets of equal preference. So if everyone followed the standards,
pointing MX'es at round-robin'ed A records shouldn't give you any better
load-balancing overall than just having a more equal-preference MX'es in the
first place.

Of course, I'm not so naive to think all implementations follow standards. But
it's hard to know what form of standards non-compliance Microsoft was trying to
accommodate with this multiple-A scheme.

Then again, when it comes to standards non-compliance, I'll defer to Microsoft,
since they appear to be the experts in that area...


- Kevin

William Stacey wrote:

> Thanks Barry.  Might round robin be another reason they implemented it this
> way?
>
> --
> William Stacey, MCSE
> Microsoft MVP Windows 2000/NT Server
>
> "Barry Margolin" <barmar at genuity.net> wrote in message
> news:a8t9dk$ptn at pub3.rc.vix.com...
> > In article <a8t8dq$pt2 at pub3.rc.vix.com>,
> > William Stacey <staceyw at mvps.org> wrote:
> > >What the advantage to doing this:
> > >;; ANSWER SECTION:
> > >microsoft.com.          6789    IN      MX      10 maila.microsoft.com.
> > >microsoft.com.          6789    IN      MX      10 mailb.microsoft.com.
> > >microsoft.com.          6789    IN      MX      10 mailc.microsoft.com.
> > >
> > >;; ADDITIONAL SECTION:
> > >maila.microsoft.com.    6789    IN      A       131.107.3.125
> > >maila.microsoft.com.    6789    IN      A       131.107.3.124
> > >mailb.microsoft.com.    6789    IN      A       131.107.3.122
> > >mailb.microsoft.com.    6789    IN      A       131.107.3.123
> > >mailc.microsoft.com.    6789    IN      A       131.107.3.121
> > >mailc.microsoft.com.    6789    IN      A       131.107.3.126
> > >
> > >As opposed to just listing more MX's like:
> > >;; ANSWER SECTION:
> > >microsoft.com.          6789    IN      MX      10 maila.microsoft.com.
> > >microsoft.com.          6789    IN      MX      10 mailb.microsoft.com.
> > >microsoft.com.          6789    IN      MX      10 mailc.microsoft.com.
> > >microsoft.com.          6789    IN      MX      10 maild.microsoft.com.
> > >microsoft.com.          6789    IN      MX      10 maile.microsoft.com.
> > >microsoft.com.          6789    IN      MX      10 mailf.microsoft.com.
> > >
> > >;; ADDITIONAL SECTION:
> > >maila.microsoft.com.    6789    IN      A       131.107.3.125
> > >mailb.microsoft.com.    6789    IN      A       131.107.3.124
> > >mailc.microsoft.com.    6789    IN      A       131.107.3.122
> > >maild.microsoft.com.    6789    IN      A       131.107.3.123
> > >maile.microsoft.com.    6789    IN      A       131.107.3.121
> > >mailf.microsoft.com.    6789    IN      A       131.107.3.126
> > >
> > >Is the advantage round-robin?
> >
> > Some mailers have a limit on the number of equal-preference MX's that
> > they'll try, possibly only one.  So if a server only tries one MX record,
> > it will still see both addresses corresponding to that server, and may try
> > both addresses.  If you had six MX records, only one address would be
> tried
> > in this case.
> >
> > --
> > Barry Margolin, barmar at genuity.net
> > Genuity, Woburn, MA
> > *** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to
> newsgroups.
> > Please DON'T copy followups to me -- I'll assume it wasn't posted to the
> group.
> >