T7557: Fix netplug hook for interface flapping

Author: sarthurdev

python/vyos/utils/network.py

@@ -666,3 +666,11 @@ def is_valid_ipv6_address_or_range(addr: str) -> bool:
             return ip_network(addr).version == 6
     except:
         return False
+
+def is_carrier_up(ifname: str) -> bool | None:
+    try:
+        carrier_path = f'/sys/class/net/{ifname}/carrier'
+        with open(carrier_path, 'r') as f:
+            return f.read().strip() == '1'
+    except:
+        return None

src/etc/netplug/vyos-netplug-dhcp-client

@@ -22,6 +22,7 @@ from time import sleep
 from vyos.config import Config
 from vyos.ifconfig import Section
 from vyos.utils.boot import boot_configuration_complete
+from vyos.utils.network import is_carrier_up
 from vyos.utils.process import cmd
 from vyos.utils.process import is_systemd_service_active
 from vyos.utils.commit import commit_in_progress
@@ -49,7 +50,8 @@ interface_path = ['interfaces'] + Section.get_config_path(interface).split()
 
 systemdV4_service = f'dhclient@{interface}.service'
 systemdV6_service = f'dhcp6c@{interface}.service'
-if in_out == 'out':
+# T7557 - Check the interface is still down at time of script
+if in_out == 'out' and not is_carrier_up(interface):
     # Interface moved state to down
     if is_systemd_service_active(systemdV4_service):
         cmd(f'systemctl stop {systemdV4_service}')