[dns-wg] DNS migration draft

Hi Fernando,

The draft looks fine for me, and as DNS administrator seems to be useful, thanks.
My duties include managing DNS servers and several domains, with full IPv6 support.
This way I found that from the IPv6 point of view some comments could be made, also from my own experience.

You can interpret me as thinking aloud:

1) In case of having IPv4 and IPv6 addresses for the DNS server of example.org domain, changing addresses in different moments could lead to reduce the blackout, at least for the dualstack user resolvers. For example:

 example.org.  NS  A    10.1.2.3
               NS  AAAA 2001:800:40:2a2f::1 

 Your change of ISP could mean just changing the IPv4 or IPv6 address range. In this case just changing one of the addresses is enough, as the other still can be used.
 If you have to change both (v6 and v4), first change one of the RRs (AAAA for example, as the default behavour is to try first the AAAA address) and when everything is stable again change the other RR (A for example).
 I understand that few DNS servers have IPv6 and IPv4 connectivity today, but this situation will be there in the future, while coexistence of IPv4 and IPv6 increase.

 2) Your solution is based on replicating equipment (having two servers), but, could this be avoided using two addresses in the same interface? Or for example installing two network cards to the server, one for each address?

 3) It is a common practice to have servers in different ASs , this way being prepared for network looses of conectivity. This could be used as a backup solution, previous the address changes. For example, you have your master DNS server in you network with your future ex-ISP. You also have one or more secondaries in other networks with addresses from other ISP(S). Before changing the addreses of you master DNS server, you can change the configuration in order to make one of the secondaries being the new master. Then, after the changes of addresses, change the whole configuration (NIC, etc.) with the new address. This involves a lot of administrative work, but seems to me as a possible solution.
 This idea is based in our experience, as we have control over DNS servers in different ASs. Looks like your section 9.1, but with no help of third-party DNS server(s).

Best regards,
Alvaro Vives
Consulintel


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