[Pdns-users] powerdns answers different on duplicate mx records

[Simon Østengaard]

I have a zone hosted on a powerdns server with mysql backend with two mx
records pointing to the same server. i.e.

mysql> select * from records where name = 'example.com' and type = 'mx'\G

*************************** 1. row ***************************
         id: 221832
  domain_id: 34786
       name: example.com
    content: mail1.example.com
        ttl: 60
       prio: 50
       type: MX
create_date: 20040526075242
change_date: 1085557962
     hidden: 0
   readonly: 0
*************************** 2. row ***************************
         id: 222723
  domain_id: 34786
       name: example.com
    content: mail2.example.com
        ttl: 60
       prio: 75
       type: MX
create_date: 20040526081803
change_date: 1085559483
     hidden: 0
   readonly: 0
*************************** 3. row ***************************
         id: 222722
  domain_id: 34786
       name: example.com
    content: mx1.example.com
        ttl: 60
       prio: 25
       type: MX
create_date: 20040526081729
change_date: 1085559449
     hidden: 0
   readonly: 0
*************************** 4. row ***************************
         id: 165835
  domain_id: 34786
       name: example.com
    content: mail1.example.com
        ttl: 60
       prio: 50
       type: MX
create_date: 20031021093913
change_date: 1066729153
     hidden: 0
   readonly: 0
*************************** 5. row ***************************
         id: 165836
  domain_id: 34786
       name: example.com
    content: mail2.example.com
        ttl: 60
       prio: 20
       type: MX
create_date: 20031117113922
change_date: 1069069162
     hidden: 0
   readonly: 0
5 rows in set (0.00 sec)

A quit odd setup, but still valid though.

When I do an mx look up on the server I get the two records with the lowest
id:

user at foobar:~$ dig @ns1.example.com example.com mx

; <<>> DiG 9.2.1 <<>> @ns1.example.com example.com mx
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 9232
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;example.com.                   IN      MX

;; ANSWER SECTION:
example.com.            60      IN      MX      50 mail1.example.com.
example.com.            60      IN      MX      20 mail2.example.com.
example.com.            60      IN      MX      25 mx1.example.com.

;; Query time: 6 msec
;; SERVER: 80.80.19.154#53(ns1.example.com)
;; WHEN: Wed May 26 09:33:35 2004
;; MSG SIZE  rcvd: 108

But when I do an axfr look up I get the two records with the highest id:

user at foobar:~$ dig @ns1.example.com example.com axfr

; <<>> DiG 9.2.1 <<>> @ns1.example.com example.com axfr
;; global options:  printcmd
example.com.            40001   IN      SOA     ns1.example.com.
user.example.com 1085559483 10800 3600 604800 40001
example.com.            86400   IN      NS      ns2.example.com.
example.com.            86400   IN      NS      ns1.example.com.
www.example.com.        60      IN      A       <an ip address>
example.com.            60      IN      MX      50 mail1.example.com.
example.com.            60      IN      MX      75 mail2.example.com.
example.com.            60      IN      MX      25 mx1.example.com.
example.com.            40001   IN      SOA     ns1.example.com.
user.example.com. 1085559483 10800 3600 604800 40001
;; Query time: 9 msec
;; SERVER: 80.80.19.154#53(ns1.example.com)
;; WHEN: Wed May 26 09:34:21 2004
;; XFR size: 9 records

Can anybody explain this behaviour?

Best regards,

Simon Østengaard
Systems Administrator