RDNSS Option should be included in ICMPv6 Router Advertisements

[Tore Anderson]

The ICMPv6 Router Advertisements on an IPv6 subnet handled by Neutron does not contain the Recursive DNS Server Option, even though the subnet has been created with an appropriate "dns_nameservers" parameter. This means that instances on a subnet using SLAAC does not learn any DNS servers, and thus cannot resolve any hostnames after being provisioned. That is likely to break lots of things, such as further provisioning of applications to the instance.

The RDNSS option is documented in RFC 6106. It can be configured in radvd.conf using the following syntax:

interface qr-foo {
  RDNSS server1 [server2 ...] {
    # this is optional, but prevents problems noted in the second bullet of
    # https://tools.ietf.org/html/draft-ietf-6man-rdnss-rfc6106bis-02#appendix-B
    AdvRDNSSLifetime infinity;
  };
};

Observed on OpenStack Kilo.

Note: It might be that using DHCPv6 in some capacity would work around this issue. I have not yet tested this, though.

[Sean M. Collins (scollins)]

Confirming this - I think this is something we need to add to our radvd orchestration code.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/236805

[Sean M. Collins (scollins)]

Adding this to Mitaka-1 since there is a patch up for this, and it's a relatively simple change to implement this feature.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/236805
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=a3e102934cee01c14d5327ae7520555bc12affdd
Submitter: Jenkins
Branch: master

commit a3e102934cee01c14d5327ae7520555bc12affdd
Author: sridhargaddam <email address hidden>
Date: Mon Oct 19 05:32:16 2015 +0000

    Support for IPv6 RDNSS Option in Router Advts

    RFC6106 standardizes IPv6 Router Advertisements to support
    Recursive DNS server information. RDNSS info allows an IPv6
    host to configure the DNS information via RA messages without
    needing DHCPv6 for the DNS configuration.

    This patch configures RADVD daemon to include RDNSS entries in
    the Router Advertisements when the IPv6 subnet has dns_nameservers.

    Closes-Bug: #1495465
    Change-Id: Ia516d40b1c7a83cd7046b2b7f42d1204f44288a9

[Ihar Hrachyshka (ihar-hrachyshka)]

FYI: Probably not backportable since it requires specific version of radvd (1.8+).

[Sridhar Gaddam (sridhargaddam)]

@Ihar, radvd seems to have RDNSS support since a long time - http://www.litech.org/radvd/

[Thierry Carrez (ttx)]

This issue was fixed in the openstack/neutron 8.0.0.0b2 development milestone.