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how to retrieve ARP entries from a router using SNMP in a perl script and print out the MAC and IP addresses and vlan

solution: a script called "getArpFromRouter.pl"
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#!/usr/bin/perl
##############################################################################
#
# This script is designed to retrieve the ARP table entries for a router using
# the Simple Network Management Protocol (SNMP) and display them in a
# human-readable format.
#
# The script first sets SNMP credentials and the target router IP address,
# then retrieves VLAN names from the IF-MIB::ifName table using the snmpwalk
# command. The VLAN names are stored in an associative array called vlannames.
# The script then walks the IP-MIB::ipNetToMediaPhysAddress table to retrieve
# ARP table entries, which contain IP addresses, MAC addresses, and VLAN IDs.
# The script uses the VLAN IDs to look up the corresponding VLAN names in the
# vlannames array, and then prints out the IP address, MAC address, VLAN name,
# and VLAN ID in a formatted table.
#
# Overall, this script provides a quick and easy way to retrieve and view ARP
# table entries for a router, which can be useful for troubleshooting network
# issues or monitoring network activity.
#
# usage: ./getArpFromRouter.pl
#
# output sample:
#
# 10.20.30.141 aa:bb:cc:1f:a5:75 vlantest 1712.
# 10.20.30.142 aa:bb:cc:1f:a5:7a vlantest 1712.
#
#
##############################################################################

use strict;
use warnings;

# Set SNMP credentials and target router IP address
my $community = "public";
my $router_ip = "192.168.2.1";

# OID for IP-MIB::ipNetToMediaPhysAddress table
my $ip_oid = "IP-MIB::ipNetToMediaPhysAddress";

# OID for IF-MIB::ifName table
my $vlan_oid = "IF-MIB::ifName";

# Set debug flag
my $debug = 1;

my %vlannames;

sub main {
# Walk the IF-MIB::ifName table and store VLAN names in an associative array
if ($debug) {
print "DEBUG: Retrieving VLAN names from $vlan_oid\n";
}

open(my $SNMPWALK, "-|", "snmpwalk -c $community -v 2c $router_ip $vlan_oid") or die "Could not run snmpwalk: $!";

while (my $line = <$SNMPWALK>) {
chomp($line);

# Extract VLAN ID and name from line
my ($vlan_id, $vlan_name) = ($line =~ /.*\.(\d+)\s+=\s+STRING:\s+(.+)/);

$vlannames{$vlan_id} = $vlan_name;

# Print VLAN name if debug flag is set
if ($debug) {
print "DEBUG: Received VLAN name: $vlan_name (VLAN ID: $vlan_id)\n";
}
}

close($SNMPWALK);

print "---- VLAN Names ----\n";

foreach my $vlan_id (keys %vlannames) {
my $vlan_name = $vlannames{$vlan_id};
print "VLAN ID: $vlan_id, VLAN name: $vlan_name\n";
}

# Walk the IP-MIB::ipNetToMediaPhysAddress table and print out VLAN name, IP, and MAC
if ($debug) {
print "DEBUG: Retrieving IP-MIB::ipNetToMediaPhysAddress table from $router_ip\n";
}

open(my $SNMPWALK, "-|", "snmpwalk -c $community -v 2c $router_ip $ip_oid") or die "Could not run snmpwalk: $!";

while (my $line = <$SNMPWALK>) {
chomp($line);
#print "$line\n" if $debug;

# Extract VLAN ID, IP, and MAC from line
my ($vlan_id) = $line =~ /IP-MIB::ipNetToMediaPhysAddress\.(\d+)/;
my ($ip) = $line =~ /IP-MIB::ipNetToMediaPhysAddress\.\d+\.(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/;
my ($mac) = $line =~ /STRING: (.+)$/;

#print " vlan_id=$vlan_id\n" if $debug;
#print " ip=$ip\n" if $debug;
#print " mac=$mac\n" if $debug;

# Look up VLAN name in associative array
my $vlan_name = $vlannames{$vlan_id};

# Print VLAN name, IP, and MAC in the desired format
printf("%-15s %-20s %-20s %-10s\n", $ip, $mac, $vlan_name, "$vlan_id.");
#exit;

}

close($SNMPWALK);
}

# Call main function
main();

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