Fix route_check.py to ignore local p2p IP prefixes

 * In some cases where there are repeated link flaps, route_check.py flags local
   p2p IP prefixes as missing in APPL_DB. These /31 IPv4 or /126 IPv6 IPs are
   not expected to be present in APPL_DB after a link goes down. This change
   tries to filter out such entries.

    Failure results: {{
        "missed_ROUTE_TABLE_routes": [
            "10.10.196.16/31",
            "2603:10b0:31f:753::24/126"
        ]
    }}
    Failed. Look at reported mismatches above
    add: []
    del: [
        "10.10.196.16/31",
        "2603:10b0:31f:753::24/126"
    ]

Signed-off-by: Prabhat Aravind <[email protected]>

Author: prabhataravind

scripts/route_check.py

@@ -398,6 +398,48 @@ def get_interfaces(namespace):
     return sorted(intf)
 
 
+def is_point_to_point_prefix(prefix):
+    """
+    check if a given prefix is a p2p /31 ipv4 prefix or a /126 ipv6 prefix
+    :return sorted list of local p2p IP prefixes
+    """
+    try:
+        network = ipaddress.ip_network(prefix, strict=False)
+        if isinstance(network, ipaddress.IPv4Network) and network.prefixlen == 31:
+            return True
+        if isinstance(network, ipaddress.IPv6Network) and network.prefixlen == 126:
+            return True
+        return False
+    except ValueError:
+        return False
+
+
+def get_local_p2p_ips():
+    """
+    helper to read p2p2 local IPs from interface table in APPL-DB.
+    :return sorted list of local p2p IP addresses
+    """
+    db = swsscommon.DBConnector(APPL_DB_NAME, 0)
+    print_message(syslog.LOG_DEBUG, "APPL DB connected for interfaces")
+    tbl = swsscommon.Table(db, 'INTF_TABLE')
+    keys = tbl.getKeys()
+
+    intf = []
+    for k in keys:
+        lst = re.split(':', k.lower(), maxsplit=1)
+        if len(lst) == 1:
+            # No IP address in key; ignore
+            continue
+
+        ip = lst[1]
+
+        if is_point_to_point_prefix(ip):
+            intf.append(ip)
+
+    print_message(syslog.LOG_DEBUG, json.dumps({"APPL_DB_INTF": sorted(intf)}, indent=4))
+    return sorted(intf)
+
+
 def filter_out_local_interfaces(namespace, keys):
     """
     helper to filter out local interfaces
@@ -413,6 +455,7 @@ def filter_out_local_interfaces(namespace, keys):
 
     db = swsscommon.DBConnector(APPL_DB_NAME, REDIS_TIMEOUT_MSECS, True, namespace)
     tbl = swsscommon.Table(db, 'ROUTE_TABLE')
+    if_tbl_ips = set(get_local_p2p_ips())
 
     for k in keys:
         e = dict(tbl.get(k)[1])
@@ -426,6 +469,9 @@ def filter_out_local_interfaces(namespace, keys):
             if not nh or ipaddress.ip_address(nh).is_unspecified:
                 continue
 
+        if k in if_tbl_ips:
+            continue
+
         rt.append(k)
 
     return rt