[2.0b5,1.9] DNS record added for non-boot interface IP when no address of that family exists on the boot interface

[Andreas Hasenack]

MAAS Version 1.9.1+bzr4543-0ubuntu2 (trusty1)

We got a situation where IPv6 was being used in a MAAS 1.9 subnet and the node failed to get a FQDN for its hostname.

Specifically, the call that failed was pyton's socket.gethostbyaddr(<hostname>), which is used by socket.getfqdn():

ubuntu@rectangular-structure:~$ python -c "import socket; print socket.gethostname()"
rectangular-structure

ubuntu@rectangular-structure:~$ python -c "import socket; print socket.gethostbyaddr(socket.gethostname())"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
socket.herror: [Errno 1] Unknown host
ubuntu@rectangular-structure:~$

A DNS traffic capture showed this:
146 2.859261 192.168.120.8 -> 198.18.173.40 DNS 88 Standard query 0x0e2a AAAA rectangular-structure.maas
147 2.859422 198.18.173.40 -> 192.168.120.8 DNS 146 Standard query response 0x0e2a AAAA rectangular-structure.maas AAAA 2001:4878:c1e0:603a:225:90ff:fe30:4b6c NS maas A 198.18.173.40
149 2.859831 192.168.120.8 -> 198.18.173.40 DNS 134 Standard query 0xd332 PTR c.6.b.4.0.3.e.f.f.f.0.9.5.2.2.0.a.3.0.6.0.e.1.c.8.7.8.4.1.0.0.2.ip6.arpa
150 2.860065 198.18.173.40 -> 192.168.120.8 DNS 196 Standard query response 0xd332 No such name PTR c.6.b.4.0.3.e.f.f.f.0.9.5.2.2.0.a.3.0.6.0.e.1.c.8.7.8.4.1.0.0.2.ip6.arpa SOA use1.akamai.com

We can see that the PTR for the IPv6 address does not exist. Looking at /etc/bind in the MAAS node, that's confirmed:
$ grep rectangular -r etc/
etc/bind/maas/zone.168.192.in-addr.arpa:8.120.168.192.in-addr.arpa. IN PTR rectangular-structure.maas.
etc/bind/maas/zone.maas:rectangular-structure IN A 192.168.120.8
etc/bind/maas/zone.maas:rectangular-structure IN AAAA 2001:4878:c1e0:603a:225:90ff:fe30:4b6c

I found it curious that MAAS would have the AAAA record, but not the corresponding PTR one, so I decided to file this bug about it.

[Andreas Hasenack (ahasenack)]

rectangular-structure node

[LaMont Jones (lamont)]

get_hostname_ip_mapping() treats ipv4 and ipv6 as completely separate things, when it tries to answer the question "what is the best IP address for this node?" This allows a discovered (and lonely) ipv6 address on a non-pxeboot interface to show up as a AAAA RR for a machine, while the A RR is AUTO or reserved or sticky.

My first thinking on this is that the two sets of records should be locked to either the same interface, or at least to the same preference order (don't provide a discovered IPv4/6 IP if there's one from DHCP of the other kind, for example.) But I want to think about it more and kick it about a little first.