Merge pull request #636 from c-po/t2562-dhcp

dhcp: T2562: add "listen-address" CLI node for better DHCP relay support

4 files changed, 64 insertions, 12 deletions

diff --git a/data/templates/dhcp-server/dhcpd.conf.tmpl b/data/templates/dhcp-server/dhcpd.conf.tmpl
index bcf425abd..56a5f4bcd 100644
--- a/data/templates/dhcp-server/dhcpd.conf.tmpl
+++ b/data/templates/dhcp-server/dhcpd.conf.tmpl
@@ -62,6 +62,14 @@ failover peer "{{ subnet_config.failover.name }}" {
 {%     endif %}
 {%   endfor %}
 {% endif %}
+{% if listen_address is defined and listen_address is not none %}
+
+# DHCP server serving relay subnet, we need a connector to the real world
+{%   for address in listen_address %}
+# Connected subnet statement for listen-address {{ address }}
+subnet {{ address | network_from_ipv4 }} netmask {{ address | netmask_from_ipv4 }} { }
+{%   endfor %}
+{% endif %}
 
 # Shared network configration(s)
 {% if shared_network_name is defined and shared_network_name is not none %}
diff --git a/interface-definitions/dhcp-server.xml.in b/interface-definitions/dhcp-server.xml.in
index 2f78f11ea..161eeed28 100644
--- a/interface-definitions/dhcp-server.xml.in
+++ b/interface-definitions/dhcp-server.xml.in
@@ -11,13 +11,13 @@
         <children>
           <leafNode name="disable">
             <properties>
-              <help>Option to disable DHCP server</help>
+              <help>Disable DHCP server</help>
               <valueless/>
             </properties>
           </leafNode>
           <leafNode name="dynamic-dns-update">
             <properties>
-              <help>DHCP server to dynamically update the Domain Name System (DNS)</help>
+              <help>Dynamically update Domain Name System (RFC4702)</help>
               <valueless/>
             </properties>
           </leafNode>
@@ -32,19 +32,20 @@
           </leafNode>
           <leafNode name="hostfile-update">
             <properties>
-              <help>Enable DHCP server updating /etc/hosts (per client lease)</help>
+              <help>Updating /etc/hosts file (per client lease)</help>
               <valueless/>
             </properties>
           </leafNode>
           <leafNode name="host-decl-name">
             <properties>
-              <help>Instruct server to use host declaration name for forward DNS name</help>
+              <help>Use host declaration name for forward DNS name</help>
               <valueless/>
             </properties>
           </leafNode>
+          #include <include/listen-address.xml.i>
           <tagNode name="shared-network-name">
             <properties>
-              <help>DHCP shared network name [REQUIRED]</help>
+              <help>Name of DHCP shared network</help>
               <constraint>
                 <regex>[-_a-zA-Z0-9.]+</regex>
               </constraint>
diff --git a/python/vyos/template.py b/python/vyos/template.py
index 5993ffd95..63d400642 100644
--- a/python/vyos/template.py
+++ b/python/vyos/template.py
@@ -123,23 +123,56 @@ def render(
 ##################################
 
 @register_filter('address_from_cidr')
-def address_from_cidr(text):
+def address_from_cidr(prefix):
     """ Take an IPv4/IPv6 CIDR prefix and convert the network to an "address".
     Example:
     192.0.2.0/24 -> 192.0.2.0, 2001:db8::/48 -> 2001:db8::
     """
     from ipaddress import ip_network
-    return str(ip_network(text).network_address)
+    return str(ip_network(prefix).network_address)
 
 @register_filter('netmask_from_cidr')
-def netmask_from_cidr(text):
+def netmask_from_cidr(prefix):
     """ Take CIDR prefix and convert the prefix length to a "subnet mask".
     Example:
       - 192.0.2.0/24 -> 255.255.255.0
       - 2001:db8::/48 -> ffff:ffff:ffff::
     """
     from ipaddress import ip_network
-    return str(ip_network(text).netmask)
+    return str(ip_network(prefix).netmask)
+
+@register_filter('netmask_from_ipv4')
+def netmask_from_ipv4(address):
+    """ Take IP address and search all attached interface IP addresses for the
+    given one. After address has been found, return the associated netmask.
+
+    Example:
+      - 172.18.201.10 -> 255.255.255.128
+    """
+    from netifaces import interfaces, ifaddresses, AF_INET
+    for interface in interfaces():
+        tmp = ifaddresses(interface)
+        if AF_INET in tmp:
+            for af_addr in tmp[AF_INET]:
+                if 'addr' in af_addr:
+                    if af_addr['addr'] == address:
+                        return af_addr['netmask']
+
+    raise ValueError
+
+@register_filter('network_from_ipv4')
+def network_from_ipv4(address):
+    """ Take IP address and search all attached interface IP addresses for the
+    given one. After address has been found, return the associated network
+    address.
+
+    Example:
+      - 172.18.201.10 has mask 255.255.255.128 -> network is 172.18.201.0
+    """
+    netmask = netmask_from_ipv4(address)
+    from ipaddress import ip_interface
+    cidr_prefix = ip_interface(f'{address}/{netmask}').network
+    return address_from_cidr(cidr_prefix)
 
 @register_filter('is_ip')
 def is_ip(addr):
diff --git a/src/conf_mode/dhcp_server.py b/src/conf_mode/dhcp_server.py
index 9be586cdf..1ab2d8d16 100755
--- a/src/conf_mode/dhcp_server.py
+++ b/src/conf_mode/dhcp_server.py
@@ -26,6 +26,7 @@ from vyos.template import render
 from vyos.util import call
 from vyos.util import dict_search
 from vyos.validate import is_subnet_connected
+from vyos.validate import is_addr_assigned
 from vyos.xml import defaults
 from vyos import ConfigError
 from vyos import airbag
@@ -246,10 +247,19 @@ def verify(dhcp):
                     if net.overlaps(net2):
                         raise ConfigError('Conflicting subnet ranges: "{net}" overlaps "{net2}"!')
 
+    for address in (dict_search('listen_address', dhcp) or []):
+        if is_addr_assigned(address):
+            listen_ok = True
+            # no need to probe further networks, we have one that is valid
+            continue
+        else:
+            raise ConfigError(f'listen-address "{address}" not configured on any interface')
+
+
     if not listen_ok:
-        raise ConfigError('DHCP server configuration error! None of the configured\n' \
-                          'subnets have an appropriate primary IP address on any\n'
-                          'broadcast interface.')
+        raise ConfigError('None of the configured subnets have an appropriate primary IP address on any\n'
+                          'broadcast interface configured, nor was there an explicit listen-address\n'
+                          'configured for serving DHCP relay packets!')
 
     return None