Marc Perkel wrote:
> Doing a reverse lookup on a misconfigured host and I get this result
> from dnsstuff.com
>
> *Preparation*:
> The reverse DNS entry for an IP is found by reversing the IP, adding it to "in-addr.arpa", and looking up the PTR record.
> So, the reverse DNS entry for 200.76.108.68 is found by looking up the PTR record for
> 68.108.76.200.in-addr.arpa.
> All DNS requests start by asking the root servers, and they let us know what to do next.
> See How Reverse DNS Lookups Work <http://www.dnsstuff.com/info/revdns.htm> for more information.
>
> *How I am searching*:
> Asking e.root-servers.net for 68.108.76.200.in-addr.arpa PTR record:
> e.root-servers.net says to go to ns2.dns.br. (zone: 200.in-addr.arpa.)
> Asking ns2.dns.br. for 68.108.76.200.in-addr.arpa PTR record:
> ns2.dns.br [200.19.119.99] says to go to B.NS.MX. (zone: 76.200.in-addr.arpa.)
> Asking B.NS.MX. for 68.108.76.200.in-addr.arpa PTR record:
> b.ns.mx [200.23.179.1] says to go to dns6m.inext.net.mx. (zone: 108.76.200.in-addr.arpa.)
> Asking dns6m.inext.net.mx. for 68.108.76.200.in-addr.arpa PTR record: Reports latam.rci.com. [from 200.76.111.202]
>
> *Answer*:
> 200.76.108.68 PTR record: *latam.rci.com.* [TTL 86400s] [A=148.243.230.2] **ERROR** A record for latam.rci.com. does not point back to original IP.
>
>
> Exim see this as the sender_host_name being blank instead of returning
> the misconfigured reverse lookup. Is there any way to just return the
> reverse lookup even if it is misconfigured?
>
>
AFAIK, Exim already *does do* - THEN makes the comparison on what it receives
and back-checks that. Might not be usr-visible, but the behaviour suggest such.
But prefixes can pose a problem, especially where a correspondent uses broken or
even 'stealth' outbound-only MTA's w/o proper DNS entries.
KISS.
$ host latam.rci.com
latam.rci.com has address 148.243.230.2
$ host 148.243.230.2
2.230.243.148.in-addr.arpa domain name pointer latam.rci.com.
Works fine.
But ...
$ host rci.com
rci.com has address 198.151.36.111
$ host 198.151.36.111
Host 111.36.151.198.in-addr.arpa not found: 3(NXDOMAIN)
Disagrees...
Is that the cause?
Bigger problem in that NetSol have been doing even worse for multiple thousands
of parked/MX-only domains... Even the <domain>.<tld> do not agree, let alone
prefixen.
Bill
