fix: the remote access clients' resolver answers on the internal address by default, chosen by p2s.dns_listen, so the name server can take port 53 of the external addresses.

debian-package/src/usr/lib/vpn-router/setup

@@ -241,10 +241,11 @@ def filter_block(ctx):
 
     pools = [pool for ready, pool in ((vpnrouter.p2s_ready(ctx), ctx['p2s_address_pool']),
                                       (vpnrouter.openvpn_ready(ctx), ctx['openvpn_pool'])) if ready]
-    if pools and ctx['local_addr_list']:
+    # The remote access clients' resolver answers on the addresses of p2s.dns_listen.
+    if pools and ctx['p2s_resolver_addrs']:
         lines += ['', '# P2S DNS RULES START']
         for pool in pools:
-            for address in ctx['local_addr_list']:
+            for address in ctx['p2s_resolver_addrs']:
                 lines += [
                     f'-A ufw-before-input -s {pool} -d {address} -p udp --dport 53 -j ACCEPT',
                     f'-A ufw-before-input -s {pool} -d {address} -p tcp --dport 53 -j ACCEPT',

debian-package/src/usr/lib/vpn-router/vpnrouter.py

@@ -53,7 +53,7 @@ SCHEMA = {
     'wan':        {'local_fqdn': ''},
     'local':      {'cidrs': [], 'int_addr': '', 'int_gateway_ip': ''},
     'site_to_site': {},
-    'p2s':        {'enabled': False, 'address_pool': ''},
+    'p2s':        {'enabled': False, 'address_pool': '', 'dns_listen': 'internal'},
     'wireguard':  {'enabled': False, 'address': '', 'listen_port': 51820},
     'openvpn':    {'enabled': False, 'address_pool': '', 'port': 1194, 'protocol': 'udp'},
     'docker':     {'mode': 'auto', 'exposed_ports': []},
@@ -581,9 +581,15 @@ def validate(cfg):
         raise ConfigError(f'dns.listen: {dns["listen"]!r} is not one of {", ".join(LISTEN_CHOICES)}')
     if not DNS_TTL_RANGE[0] <= dns['ttl'] <= DNS_TTL_RANGE[1]:
         raise ConfigError(f'dns.ttl: {dns["ttl"]} is not between {DNS_TTL_RANGE[0]} and {DNS_TTL_RANGE[1]} seconds')
-    if dns['enabled'] and dns['listen'] != 'internal' and (_get(cfg, 'p2s', 'enabled') or _get(cfg, 'openvpn', 'enabled')):
-        raise ConfigError('dns.listen: port 53 of the external addresses is the resolver of the remote access clients '
-                          'while p2s.enabled or openvpn.enabled is true; the name server can listen on internal only')
+    resolver_listen = _get(cfg, 'p2s', 'dns_listen')
+    if resolver_listen not in LISTEN_CHOICES:
+        raise ConfigError(f'p2s.dns_listen: {resolver_listen!r} is not one of {", ".join(LISTEN_CHOICES)}')
+    sides = {'internal': {'internal'}, 'external': {'external'}, 'both': {'internal', 'external'}}
+    if dns['enabled'] and (_get(cfg, 'p2s', 'enabled') or _get(cfg, 'openvpn', 'enabled')) and \
+            sides[dns['listen']] & sides[resolver_listen]:
+        raise ConfigError(f'dns.listen: port 53 of the {" and ".join(sorted(sides[dns["listen"]] & sides[resolver_listen]))} '
+                          f'addresses is the resolver of the remote access clients (p2s.dns_listen {resolver_listen}) '
+                          'while p2s.enabled or openvpn.enabled is true')
 
     for option in ('root_name', 'p2s_name', 's2s_name'):
         value = _get(cfg, 'pki', option)
@@ -933,6 +939,10 @@ def build_context(cfg, public_ip=None):
     openvpn_pool = _get(cfg, 'openvpn', 'address_pool')
     openvpn_network = ipaddress.ip_network(openvpn_pool) if openvpn_pool else None
     identities = {'fqdn': local_fqdn, 'public_ip': public_ip or '', 'internal_ip': int_addr}
+    # The addresses the remote access clients' resolver answers on, which p2s.dns_listen chooses.
+    resolver_addrs = [address for address in {'internal': [int_addr], 'external': local_addrs,
+                                               'both': [int_addr, *local_addrs]}[_get(cfg, 'p2s', 'dns_listen')]
+                      if address]
 
     connections = []
     for name, connection in cfg['site_to_site'].items():
@@ -976,7 +986,8 @@ def build_context(cfg, public_ip=None):
         'p2s_enabled':     _get(cfg, 'p2s', 'enabled'),
         'p2s_address_pool': _get(cfg, 'p2s', 'address_pool'),
         'public_ip':       public_ip or '',
-        'p2s_dns':         _join(local_addrs, _split_list(extras['EXTRA_P2S_DNS'])),
+        'p2s_resolver_addrs': resolver_addrs,
+        'p2s_dns':         _join(resolver_addrs, _split_list(extras['EXTRA_P2S_DNS'])),
         'wg_enabled':      _get(cfg, 'wireguard', 'enabled'),
         'wg_address':      _get(cfg, 'wireguard', 'address'),
         'wg_listen_port':  _get(cfg, 'wireguard', 'listen_port'),
@@ -994,7 +1005,7 @@ def build_context(cfg, public_ip=None):
         'openvpn_ldap_conf': str(OPENVPN_LDAP),
         'openvpn_status':  vpnrouter_status.OPENVPN_STATUS,
         'openvpn_status_seconds': vpnrouter_status.OPENVPN_STATUS_SECONDS,
-        'p2s_dns_list':    _split_list(_join(local_addrs, _split_list(extras['EXTRA_P2S_DNS']))),
+        'p2s_dns_list':    _split_list(_join(resolver_addrs, _split_list(extras['EXTRA_P2S_DNS']))),
         'openvpn_ca':      str(vpnrouter_pki.OPENVPN_CA),
         'openvpn_crl':     str(vpnrouter_pki.OPENVPN_CRL),
         'server_cert':     str(vpnrouter_pki.VPN_SERVER_CERT),
@@ -1218,7 +1229,8 @@ def configure(cfg=None, public_ip=None):
     elif remove(ROAD_WARRIOR):
         changed.add('swanctl')
 
-    if p2s_ready(ctx) or openvpn_ready(ctx):
+    # The resolver of the remote access clients answers on the addresses of p2s.dns_listen only.
+    if (p2s_ready(ctx) or openvpn_ready(ctx)) and ctx['p2s_resolver_addrs']:
         if render(env, ctx, 'p2s-forwarder.conf.j2', P2S_FORWARDER, 0o644):
             changed.add('resolved')
     elif remove(P2S_FORWARDER):

debian-package/src/usr/lib/vpn-router/vpnrouter_platforms/azure.py

@@ -4,8 +4,8 @@ No platform-specific configuration is currently required.
 
 The Azure platform resolver 168.63.129.16 is deliberately *not* advertised to
 road-warrior clients and *not* added to the traffic selectors. Clients are
-given the router itself as their DNS server, and the router forwards through
-its own systemd-resolved via the p2s-forwarder drop-in. That resolves
+given the router's addresses of p2s.dns_listen as their DNS servers, and the router
+forwards through its own systemd-resolved via the p2s-forwarder drop-in. That resolves
 Azure-internal names without routing the wireserver address through the tunnel
 and without a second resolver in the pool.
 """

debian-package/src/usr/share/doc/vpn-router/vpn-router.json.example

@@ -38,7 +38,8 @@
   },
   "p2s": {
     "enabled": false,
-    "address_pool": "172.16.0.0/24"
+    "address_pool": "172.16.0.0/24",
+    "dns_listen": "internal"
   },
   "wireguard": {
     "enabled": false,

debian-package/src/usr/share/vpn-router/templates/p2s-forwarder.conf.j2

@@ -1,4 +1,4 @@
 [Resolve]
-{% for address in local_addr_list -%}
+{% for address in p2s_resolver_addrs -%}
 DNSStubListenerExtra={{ address }}
 {% endfor -%}