dhcp-server: T3936: Added support for DHCP Option 82 (#4665)

* dhcp-server: T3936: Added support for DHCP Option 82

This commit adds support in both the CLI and the underlying code for
DHCP Option 82 to be used to filter/route DHCP address assignments.

The primary use case for this is to support enterprise switches which
can "tag" DHCP requests with physical real world informaiton such as
which switch first saw the request and which port it originated from
(known in this context as remote-id and circuit-id). Once
client-classes have been defined they can be assigned to subnets or
ranges so that only certain addresses get assigned to specific
requests.

There is also a corresponding documentation update which pairs with
this code change.

(cherry picked from commit 326b5e713cb363a2b9f69e2204c4ee2ccd9939bb)

* Update src/conf_mode/service_dhcp-server.py

Co-authored-by: Nataliia S. <81954790+natali-rs1985@users.noreply.github.com>

* Update src/conf_mode/service_dhcp-server.py

Co-authored-by: Nataliia S. <81954790+natali-rs1985@users.noreply.github.com>

* Update interface-definitions/include/dhcp/dhcp-server-common-config.xml.i

Co-authored-by: Nataliia S. <81954790+natali-rs1985@users.noreply.github.com>

---------

Co-authored-by: Daniil Baturin <daniil@baturin.org>
Co-authored-by: Nataliia S. <81954790+natali-rs1985@users.noreply.github.com>

2 files changed, 44 insertions, 0 deletions

diff --git a/python/vyos/kea.py b/python/vyos/kea.py
index f48cf293d..323fded5d 100644
--- a/python/vyos/kea.py
+++ b/python/vyos/kea.py
@@ -179,6 +179,9 @@ def kea_parse_subnet(subnet, config):
     if 'ping_check' in config:
         out['user-context']['enable-ping-check'] = True
 
+    if 'client_class' in config:
+        out['client-class'] = config['client_class']
+
     if 'range' in config:
         pools = []
         for num, range_config in config['range'].items():
@@ -194,6 +197,9 @@ def kea_parse_subnet(subnet, config):
                 if 'bootfile_server' in range_config['option']:
                     pool['next-server'] = range_config['option']['bootfile_server']
 
+            if 'client_class' in range_config:
+                pool['client-class'] = range_config['client_class']
+
             pools.append(pool)
         out['pools'] = pools
 
@@ -677,3 +683,22 @@ def kea_get_server_leases(config, inet, vrf_name, pools=[], state=[], origin=Non
                     data.pop(idx)
 
     return data
+
+def _build_relay_hex_condition(sub_option_index, value):
+    if value.startswith("0x"):
+        return f"relay4[{sub_option_index}].hex == {value}"
+    else:
+        return f"relay4[{sub_option_index}].hex == 0x{value.encode().hex().lower()}"
+
+def kea_build_client_class_test(config):
+    conditions = []
+
+    if "relay_agent_information" in config:
+        if "circuit_id" in config["relay_agent_information"]:
+            conditions.append(_build_relay_hex_condition(1, config["relay_agent_information"]["circuit_id"]))
+        if "remote_id" in config["relay_agent_information"]:
+            conditions.append(_build_relay_hex_condition(2, config["relay_agent_information"]["remote_id"]))
+
+    test = " and ".join(conditions)
+
+    return test
diff --git a/python/vyos/template.py b/python/vyos/template.py
index f384f752d..44278e963 100755
--- a/python/vyos/template.py
+++ b/python/vyos/template.py
@@ -914,6 +914,25 @@ def kea_high_availability_json(config):
 
     return dumps(data)
 
+@register_filter('kea_client_class_json')
+def kea_client_class_json(client_classes):
+    from vyos.kea import kea_build_client_class_test
+    from json import dumps
+    out = []
+
+    for name, config in client_classes.items():
+        if 'disable' in config:
+            continue
+
+        client_class = {
+            'name': name,
+            'test': kea_build_client_class_test(config)
+        }
+
+        out.append(client_class)
+
+    return dumps(out, indent=4)
+
 @register_filter('kea_dynamic_dns_update_main_json')
 def kea_dynamic_dns_update_main_json(config):
     from vyos.kea import kea_parse_ddns_settings