[BEHAVE] RFC6147 and RFC7208 interoperability issues

[Klaus Frank <[e-mail]>]

Hi,

we had some issues with SPF and a mail server that was behind 
NAT64+DNS64. I at first thought that it was just a misconfiguration. But 
after the DNS64 server seamed to work as intended I went to the 
implementation and the RFC. Thereby while reading RFC6147 I stumbled 
across section 5.3.3 which says "All other RRs MUST be returned 
unchanged." which is the cause of my issues. This section is basically 
ignoring SPF records (RFC7208 section 5.6) and also preventing DNS64 
implementations from addressing this limitation.

Would it be possible to create an extension to RFC6147 that mandates SPF 
record rewrites as well? Otherwise Mail servers behind NAT64+DNS64 in 
IPv6 only environments won't be able to work as expected.

Like:
If the DNS64 server receives a SPF-record (within either the TXT-RR or 
the SPF-RR [RFC4408]) containing the "ip4" mechanism it MUST rewrites 
the ipv4 address according to the same rules as A-records are and 
synthesizes a new SPF record within the response that contains 
additional "ip6" entries. The original "ip4" should not be removed from 
the response.

Sincerely,
Klaus Frank