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Ichnafi's avatar
Ichnafi
Icon for Cirrostratus rankCirrostratus
Jul 12, 2021

LTM - Monitor with "arping" relies on ARP-Cache

Hello fellow F5ers,   I have devices, that can only be monitored via "arping" (don't ask, the devices are stupidly designed, some people may call that "secure"). There are several threads here on d...
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LTM
dsn_support's avatar
dsn_support
Icon for Nimbostratus rankNimbostratus
Jan 16, 2025

Hello,

I'm trying to implement the arping monitor without success.

I've created a bash file as follows:

 

#!/bin/bash
IP=$1
INTERFACE="VLAN434"  # Use the VLAN name which connect with the endpoint nodes.
 
arping -c 1 -I $INTERFACE $IP > /dev/null 2>&1
if [ $? -eq 0 ]; then
    echo "UP"
    exit 0
else
    echo "DOWN"
    exit 1
fi

I've tested this command locally an work fine, but once that I've import the file via "System  ››  File Management : External Monitor Program File List" it appears under monitor section but I cannot apply to a current defined Node..

Once that I create the monitor also I don't know if I've created correctly the monitor, see attached image.

Please, can someone help me with the exact configuration?

Thanks in advance.

 

dsn_support's avatar
dsn_support
Icon for Nimbostratus rankNimbostratus
Jan 21, 2025

Hi, I'm going to reply myself... I've finally have it working like a charm.... changes that I've made:

Monitor definition: 

  • delete all variables previously defined
  • Arguments: $F5_MONITOR_ADDRESS
  • Alias Service Port: 1  <---- this is because if you define the node in the pool as "* you cannot assign a monitor which service port is also "*" so you have to define and invented port.

And in System  ››  File Management : External Monitor Program File List: 

!/bin/bash
IP=$1
INTERFACE="VLAN_1234"  #Statically defined
# clear arp cache table to avoid false positives 
tmsh delete /net arp $IP
# execute the command:
RESULT=$(arping -c 1 -w 2 -I $INTERFACE $IP 2>&1)
# evaluate the result
if echo "$RESULT" | grep -q "Received 1 response(s)"; then
    echo "UP"
else
fi

And that's all, Iv'e applied the new monitor to the pool definition and the nodes inside the pool inherit the pool monitor.

Regards