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Algorithm for sorting response in a round-robin DNS configuration

Answer 1

+1 A:

Depending on the language you're using, putting all the answers in a hash/dictionary with an array for the leafs according to type/address, would probably be simpler.

I'd recommend tie::sorted::array::lazy if you use perl.

Perlchild 2010-01-10 19:34:03

Does the 'ruby' tag not give you a hint as to language?

womble 2010-01-10 20:28:51

This is exactly the rule I figured out. It seems to be the most reasonable solution.

Simone Carletti 2010-01-11 13:15:34

Answer 2

A:

There should be a library available for most programming languages to get a list of ip addresses for a given hostname. It'll be something like gethostbyname which will return an array of IP addresses which you can sort like any standard array. In PHP it's gethostbynamel, In Ruby it's Socket::gethostbyname.

There's no need to go through the process of getting DNS records yourself, but if you really want to then the DNS rules are quite simple. A hostname will either return a CNAME or an A record (presuming we are just dealing with IPv4); an A record will return IP addresses, if you get a CNAME you'll want to use recursion to get the A records of the CNAME result.

kaerast 2010-01-10 23:31:10

I don't need a library to get DNS records. I need to figure out an efficient algorithm to sort the response.

Simone Carletti 2010-01-11 11:38:13

Answer 3

A:

Get list of IP addresses.
Convert IP addresses to integer representation.
Sort IP addresses by integer representation.
Profit.

David Mackintosh 2010-01-10 23:52:05

It won't work because, as explained in my answer, there are some exceptions. You can't simply sort all records in the response because a CNAME record can't be compared with an A record and so forth.

Simone Carletti 2010-01-11 11:37:25

Answer 4

A:

Can you please explain why you need to sort them?

Generally the order of DNS records within each section of a packet is irrelevant. Nor is it guaranteed that two successive queries will return the same subset of possible records.

Alnitak 2010-01-11 10:48:05

I need to sort them because a sorted list it's more efficient when you have to compare thousands of records later.

Simone Carletti 2010-01-11 11:36:49

The just write them into a dababase and sort them when you need to compare them.C.

symcbean 2010-01-11 12:12:59

This is exaclty what I do. The question is an other: is there any kind of reference for sorting the answer section. As explained in my question, I can't simply order the answer by IP because some records have higher precedence depending on the original query.

Simone Carletti 2010-01-11 12:43:00

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Algorithm for sorting response in a round-robin DNS configuration

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