On Tue, Apr 3, 2012 at 8:52 AM, Ron White <[email protected]> wrote:
> I've been working with a client running Exim on a cheap shared host who > has been having some odd delivery issues. Normally I don't get too > involved in these, but it was interesting. It only affects some > recipients some of the time and the only reason I can find for the > inconstancy is what appears to be a bit of a hooky DNS set up. > > Can someone just give me a logic check here? > > The host concerned has a PTR record, it's a bit of a mess, but it's > there: > dig -x 205.134.224.208 > > 208.224.134.205.in-addr.arpa. 17019 IN CNAME > 208.128-255.224.134.205.in-addr.arpa. > 208.128-255.224.134.205.in-addr.arpa. 65020 IN PTR > whub28.webhostinghub.com. > > So this basically gives back hostname: whub28.webhostinghub.com. > > However, digging this gives two A records/IP's back rotating on a round > robin: > > dig +short whub28.webhostinghub.com. > 205.134.241.17 > 205.134.224.208 > dig +short whub28.webhostinghub.com. > 205.134.224.208 > 205.134.241.17 > dig +short whub28.webhostinghub.com. > 205.134.241.17 > 205.134.224.208 > > I think this may be a problem with PTR resolution because if the reverse > lookup for a connecting IP gives the name whub28.webhostinghub.com, but > the matching double check on that back to an IP gives two records back > will the average mail resolver see both of these and satisfy the check, > or will it take the top one only and spot the mismatch between the > original connecting IP and the RrDNS? > > Basically, is this OK or is it sub optimal/likely to break any RFC's? > To me it looks like a cheap attempt at load balancing / redundancy in > DNS - but it is probably perfectly legal, even if it may break RrDNS for > some receiving mail engines. > > Any input, reasoning greatly appreciated. > > Warm regards > Ron > > > > Hi Ron, I believe the behavior you are seeing is a 'feature' of DNS that was intended for Load Balancing, I think this RFC explains or is at least related to the functionality: http://tools.ietf.org/html/rfc1794 I don't think this configuration breaks DNS by its very existence, but in my experience with DNS administrators it seems trivially easy to do by mistake. -- ## List details at https://lists.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://wiki.exim.org/
