Forum - DNS: A, AAAA, CNAME/wildcard records :: SixXS

DNS: A, AAAA, CNAME/wildcard records

Shadow Hawkins on Tuesday, 13 December 2011 10:47:56

Hi My web host gives me several IPv6 addresses for my different sub domains, but I have the same IPv4 address. So I want to setup something like: A records:

domain.dk 203.0.113.10 *.domain.dk 203.0.113.10

AAAA records:

domain.dk 2001:DB8::10 *.domain.dk 2001:DB8::10 sub.domain.dk 2001:DB8::[bold]15[/bold]

With this config, no IPv6 is returned for sub.domain.dk, because I have a specific record in AAAA? /Kim

DNS: A, AAAA, CNAME/wildcard records

Jeroen Massar SixXS Staff

on Tuesday, 13 December 2011 10:55:38

With this config, no IPv6 is returned for sub.domain.dk, because I have a specific record in AAAA?

You mean "no IPv4 is returned", and indeed, the more specific wins. You would have to repeat the IPv4 address for that to work. But please remember that wildcards are evil and there are very few cases where they actually make any sense at all.

DNS: A, AAAA, CNAME/wildcard records

Shadow Hawkins on Tuesday, 13 December 2011 11:06:11

You mean "no IPv4 is returned", and indeed, the more specific wins. You would have to repeat the IPv4 address for that to work.

Thanks! I already knew that, but I wasn't thinking A and AAAA records was the "same" :-)

But please remember that wildcards are evil and there are very few cases where they actually make any sense at all.

How are they evil? Can you give me a case where it is a really bad idea?

DNS: A, AAAA, CNAME/wildcard records

Jeroen Massar SixXS Staff

on Tuesday, 13 December 2011 11:30:11

Thanks! I already knew that, but I wasn't thinking A and AAAA records was the "same" :-)

They are not, but if you ask your DNS server for sub.domain.dk then only the sub.domain.dk, which only has an AAAA record, is returned, the wildcard is then not looked at as there is a more specific.

How are they evil?

Can you give me a case where it is a really bad idea?

They never do what you expect them to do as can be seen above.

DNS: A, AAAA, CNAME/wildcard records

Shadow Hawkins on Tuesday, 13 December 2011 14:59:09

They never do what you expect them to do as can be seen above.

Yes, because I didn't know how this works. In other cases it saves a lot of time configuring DNS. But thanks for your help! :-)

DNS: A, AAAA, CNAME/wildcard records

Jeroen Massar SixXS Staff

on Tuesday, 13 December 2011 15:18:15

In other cases it saves a lot of time configuring DNS.

If you want to save time stuff the entries in a database (eg see PowerDNS for a complete solution) or generate the DNS zones. Then you can only make the typo in one place.

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