[arp_update]: Flush neighbors with incorrect MAC info (sonic-net#17238)

 [arp_update]: Flush MAC mismatch neighbors

- Check for MAC mismatch between neighbor entries in the kernel and APPL_DB
- Flush any entries with a mismatch

Author: theasianpianist

files/scripts/arp_update

@@ -9,6 +9,11 @@
 
 ARP_UPDATE_VARS_FILE="/usr/share/sonic/templates/arp_update_vars.j2"
 
+# Overload `logger` command to include arp_update tag
+logger () {
+    command logger -t "arp_update" "$@"
+}
+
 while /bin/true; do
   # find L3 interfaces which are UP, send ipv6 multicast pings
   ARP_UPDATE_VARS=$(sonic-cfggen -d -t ${ARP_UPDATE_VARS_FILE})
@@ -19,7 +24,7 @@ while /bin/true; do
       STATIC_ROUTE_IFNAMES=($(echo $ARP_UPDATE_VARS | jq -r '.static_route_ifnames'))
       # on supervisor/rp exit the script gracefully
       if [[ -z "$STATIC_ROUTE_NEXTHOPS" ]] || [[ -z "$STATIC_ROUTE_IFNAMES" ]]; then
-          logger "arp_update: exiting as no static route in packet based chassis"
+          logger "exiting as no static route in packet based chassis"
           exit 0
       fi
       for i in ${!STATIC_ROUTE_NEXTHOPS[@]}; do
@@ -38,7 +43,7 @@ while /bin/true; do
               interface="${STATIC_ROUTE_IFNAMES[i]}"
               if [[ -z "$interface" ]]; then
                   # should never be here, handling just in case
-                  logger "ERR: arp_update: missing interface entry for static route $nexthop"
+                  logger -p error "missing interface entry for static route $nexthop"
                   continue
               fi
               intf_up=$(ip link show $interface | grep "state UP")
@@ -47,7 +52,7 @@ while /bin/true; do
                   eval $pingcmd
                   # STALE entries may appear more often, not logging to prevent periodic syslogs
                   if [[ -z $(echo ${neigh_state} | grep 'STALE') ]]; then
-                      logger "arp_update: static route nexthop not resolved ($neigh_state), pinging $nexthop on $interface"
+                      logger "static route nexthop not resolved ($neigh_state), pinging $nexthop on $interface"
                   fi
               fi
           fi
@@ -70,6 +75,30 @@ while /bin/true; do
       fi
   done
 
+  # find neighbor entries with aged MAC and flush/relearn them
+  STALE_NEIGHS=$(ip neigh show | grep -v "fe80" | grep "STALE" | awk '{print $1 "," $5}' | tr [:lower:] [:upper:])
+  for neigh in $STALE_NEIGHS; do
+        ip="$( cut -d ',' -f 1 <<< "$neigh" )"
+        mac="$( cut -d ',' -f 2 <<< "$neigh" )"
+        if [[ -z $(sonic-db-cli ASIC_DB keys "ASIC_STATE:SAI_OBJECT_TYPE_FDB_ENTRY*${mac}*") ]]; then
+            timeout 0.2 ping -c1 -w1 $ip > /dev/null
+        fi
+  done
+
+  # Flush neighbor entries with MAC mismatch between kernel and APPL_DB
+  KERNEL_NEIGH=$(ip neigh show | grep -v "fe80" | grep -v "FAILED\|INCOMPLETE" | cut -d ' ' -f 1,3,5 --output-delimiter=',' | tr -d ' ')
+  for neigh in $KERNEL_NEIGH; do
+        ip="$( cut -d ',' -f 1 <<< "$neigh" )"
+        intf="$( cut -d ',' -f 2 <<< "$neigh" )"
+        kernel_mac="$( cut -d ',' -f 3 <<< "$neigh" )"
+        appl_db_mac="$(sonic-db-cli APPL_DB hget NEIGH_TABLE:$intf:$ip neigh)"
+        if [[ $kernel_mac != $appl_db_mac ]]; then
+            logger -p warning "MAC mismatch for ${ip} on ${intf} - kernel: ${kernel_mac}, APPL_DB: ${appl_db_mac}"
+            ip neigh flush $ip
+            timeout 0.2 ping -c1 -w1 $ip > /dev/null
+        fi
+  done
+
   VLAN=$(echo $ARP_UPDATE_VARS | jq -r '.vlan')
   SUBTYPE=$(sonic-db-cli CONFIG_DB hget 'DEVICE_METADATA|localhost' 'subtype' | tr '[:upper:]' '[:lower:]')
   for vlan in $VLAN; do
@@ -158,11 +187,11 @@ while /bin/true; do
           if [[ $ip == *"."* ]] && [[ ! $KERNEIGH4 =~ "${ip},${intf}" ]]; then
               pingcmd="timeout 0.2 ping -I $intf -n -q -i 0 -c 1 -W 1 $ip >/dev/null"
               eval $pingcmd
-              logger "arp_update: mismatch arp entry, pinging ${ip} on ${intf}"
+              logger "mismatch arp entry, pinging ${ip} on ${intf}"
           elif [[ $ip == *":"* ]] && [[ ! $KERNEIGH6 =~ "${ip},${intf}" ]]; then
               ping6cmd="timeout 0.2 ping6 -I $intf -n -q -i 0 -c 1 -W 1 $ip >/dev/null"
               eval $ping6cmd
-              logger "arp_update: mismatch v6 nbr entry, pinging ${ip} on ${intf}"
+              logger "mismatch v6 nbr entry, pinging ${ip} on ${intf}"
           fi
       fi
   done