dhcpv6: T2961: support stateless dhcpv6 clients

This commit adds support for configuring the DHCPv6 server to serve
"stateless" DHCPv6 clients (those that send an information-request
message and do not request an address).

The change introduces a `common-options` node at the
`shared-network-name` level, which allows specifying options
applicable to clients regardless of subnet assigned (or in the case of
stateless clients, when no subnet is assigned). Parameters specified
at the subnet level take precedence over those set at the
shared-network level.

Presently, only parameters that are meaningful to stateless clients
have been exposed under `common-options`, as there is no precedent of
exposing parameters at multiple levels under the current DHCPv4 or
DHCPv6 configuration syntax. If desired, additional parameters could
certainly be added with relative ease.

1 files changed, 26 insertions, 0 deletions

diff --git a/src/conf_mode/dhcpv6_server.py b/src/conf_mode/dhcpv6_server.py
index 4ce4cada1..1777d4db7 100755
--- a/src/conf_mode/dhcpv6_server.py
+++ b/src/conf_mode/dhcpv6_server.py
@@ -65,6 +65,7 @@ def get_config(config=None):
             config = {
                 'name': network,
                 'disabled': False,
+                'common': {},
                 'subnet': []
             }
 
@@ -72,6 +73,31 @@ def get_config(config=None):
             if conf.exists(['disable']):
                 config['disabled'] = True
 
+            # Common options shared among subnets. These can be overridden if
+            # the same option is specified on a per-subnet or per-host
+            # basis. These are the only options that can be handed out to
+            # stateless clients via an information-request message.
+            if conf.exists(['common-options']):
+                conf.set_level(base + ['shared-network-name', network, 'common-options'])
+
+                # How often stateless clients should refresh their information. This is
+                # mostly taken as a hint by clients, and only if they request it.
+                #  (if not specified, the server does not supply this to the client)
+                if conf.exists(['info-refresh-time']):
+                    config['common']['info_refresh_time'] = conf.return_value(['info-refresh-time'])
+
+                # The domain-search option specifies a 'search list' of Domain Names to be used
+                # by the client to locate not-fully-qualified domain names.
+                if conf.exists(['domain-search']):
+                    config['common']['domain_search'] = conf.return_values(['domain-search'])
+
+                # Specifies a list of Domain Name System name servers available to the client.
+                # Servers should be listed in order of preference.
+                if conf.exists(['name-server']):
+                    config['common']['dns_server'] = conf.return_values(['name-server'])
+
+                conf.set_level(base + ['shared-network-name', network])
+
             # check for multiple subnet configurations in a shared network
             if conf.exists(['subnet']):
                 for net in conf.list_nodes(['subnet']):