dns: T5113: Support custom port for name-server forwarders

Support custom port for name-server forwarders that would allow using
custom ports in name server forwarders to enable forwarding to
alternative name servers (unbound, stubby, dnscrypt-proxy etc.)
operating on non-default port.

This would also allow using DNS Over TLS in PowerDNS Recursor 4.6 onwards
(pdns doesn't support certificate check for validity yet) by enabling
'dot-to-port-853'. This is set by default if compiled in with DoT support.
See: https://doc.powerdns.com/recursor/settings.html#dot-to-port-853

This also partially implements T921, T2195 (DoT without certificate check).

Implementation details:
- In 'dns/forwarding' configuration, 'name-server' now allows optional
  'port' (defaults to 53).
- Instead of modifying 'name-server-ipv4-ipv6.xml.i' to add optional
  'port', a new file 'name-server-ipv4-ipv6-port.xml.i' has been used
  to avoid impacting other places where it is reused because not all of
  them honor ports (mostly VPN related).
- The `host:port` entries to be used by PowerDNS recursor config are
  normalized eagerly at the point of loading VyOS `Config` instead of
  doing them lazily while rendering the Jinja2 template to keep the
  implementation less intrusive. The alternative would entail making
  quite a bit of change in how 'vyos-hostsd' processes 'static'
  'name_servers' entries or persists their runtime states.

1 files changed, 25 insertions, 0 deletions

diff --git a/interface-definitions/include/name-server-ipv4-ipv6-port.xml.i b/interface-definitions/include/name-server-ipv4-ipv6-port.xml.i
new file mode 100644
index 000000000..cf86e66a2
--- /dev/null
+++ b/interface-definitions/include/name-server-ipv4-ipv6-port.xml.i
@@ -0,0 +1,25 @@
+<!-- include start from name-server-ipv4-ipv6-port.xml.i -->
+<tagNode name="name-server">
+  <properties>
+    <help>Domain Name Servers (DNS) addresses</help>
+    <valueHelp>
+      <format>ipv4</format>
+      <description>Domain Name Server (DNS) IPv4 address</description>
+    </valueHelp>
+    <valueHelp>
+      <format>ipv6</format>
+      <description>Domain Name Server (DNS) IPv6 address</description>
+    </valueHelp>
+    <constraint>
+      <validator name="ipv4-address"/>
+      <validator name="ipv6-address"/>
+    </constraint>
+  </properties>
+  <children>
+    #include <include/port-number.xml.i>
+    <leafNode name="port">
+      <defaultValue>53</defaultValue>
+    </leafNode>
+  </children>
+</tagNode>
+<!-- include end -->