> > I know this is a bit late but: > > Section 5.1's sythesis of MX records based on the presence of > AAAA records is a bad idea. > > If no MX records are found, but an address > RR (i.e., either an IPv4 A RR or an IPv6 AAAA RR, or their > successors) is found, the address RR is treated as if it was > associated with an implicit MX RR, with a preference of 0, pointing > to that host. > > Synthesizing a MX record on NODATA to a MX lookup and a > subsequent successful AAAA lookup is bad engineering decision. > It will work reasonably well for IPv4 only + dual stack > envirionment. It will not work well for IPv4 only + dual > stack + IPv6 only envirionment. > > The reason it is a bad engineering decision is that: > > * the IPv4 only world needs a MX RRSet to find a dual stack > MTA to relay into the IPv6 network. > > * the IPv6 world has a raft of solutions which will allow it > to initiate a connection to a IPv4 only MTA without having > to find a dual stack MX for the target mail domain. > > * it changes the definition of what it means to exist in > the mail domain and you will have different MTA/MSA making > different existance decisions. Some will say that AAAA + > no MX exist but others will say that the site does not > exist. > > e.g. > a new (IPv6 aware) MSA which is configured to relay through > a old (non-AAAA aware) MTA on its outward bound path. > > Do you really thing we should be trying to force a upgrade > of all MTA's on the planet to support MX synthesis from > AAAA when there is no engineering need to to this? > > MX from A was a transition strategy. IPv6 only sites have a > transition strategy that doesn't require synthesis. It is > advertise a dual stack MX. At some point in the future sites > will stop having a dual stack MX, the same way they stopped > adding A records for mail only domains back in the 90's. > > Mark It should be noted that direct to address for IPv4 or IPv6 addesses is reasonable when there isn't any appropriate records (MX, A or AAAA) in the DNS and the MTA is configured to use /etc/host, NIS etc. Mark -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews@xxxxxxx _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf