Add DNS-SD support to virtual DNS server

[Marcel Wiget]

Contrail-Controller supports virtual DNS to resolve the DNS requests from the VMs. Multiple virtual domain name servers under each domain in the system are supported. Each virtual domain name server is an authoritative server for the DNS domain configured.

Static DNS entries can be added but are limited to A, CNAME, PTR and NS records. Each record takes the type (A / CNAME / PTR / NS), class (IN), name, data and TTL values.

This Bug (actually feature) request asks to enhance DNS support to add and remove the following new record types:

1) Enhance PTR record (beyond reverse lookup) by allowing it to refer to domain names
2) Add support for SRV and TXT records

Background:

Service discovery via DNS is defined in RFC 6763 http://tools.ietf.org/html/rfc6763 and allows clients on a virtual network to discover services of various types, including file servers, web pages, streaming servers etc.

Clients query the name server for the given domain if service browsing is supported or not by resolving lb._dns-sd._ud. Followed by a request to resolve specific service records.

E.g. a file service can be registered statically in DNS by adding the following records:

; To direct clients to browse a different domain, substitute that domain in place of '@'
lb._dns-sd._udp PTR @

; In the list of services below, the SRV records will typically reference dot-local Multicast DNS names.
; When transferring this zone file data to your unicast DNS server, you'll need to replace those dot-local
; names with the correct fully-qualified (unicast) domain name of the target host offering the service.

_smb._tcp PTR FILESERVER._smb._tcp
FILESERVER._smb._tcp SRV 0 0 445 FILESERVER.localdomain. ; Replace with unicast FQDN of target host
FILESERVER._smb._tcp TXT "netbios="

FILESERVER IN A 1.1.1.1

The exact syntax can be found for existing services on LAN on OS/X with the following CLI command:

dns-sd -Z _smb._tcp

(replace smb and tcp with the correct service type).