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Auto-Discovery with NMAP

June 26th, 2017

Discover

I created this script in order to use it as a feed for enterprise management tools such as Nagios.   It’s a bit difficult to get a handle on auto-discovery tools within an enterprise management tool when it discovers what can be an overwhelming number of hosts.  NMAP is smart enough to translate the MAC address into a vendor if it can.

This script called discover uses the NMAP tool on Linux (tested on Centos).


#! /bin/bash
#
# Name: discover
#
# Garland Joseph, garland.joseph@gmail.com
# Date: June 2017
#
# Auto-discover on subnet using nmap, can be fed into something like nagios
# as a seed file after proper formatting.
#
# ----

if [[ -z ${1} ]]
then
cat <<EOD
$0 <subnet>
where
subnet, by example, is something like 192.168.1.0/24
EOD
exit
fi

nmap -sn ${1} | awk '
BEGIN{ printf("%-16s| %-18s| %-35s| %-30s\n","IP","MAC","NAME","VENDOR") }
/^Nmap scan report/ {
NAME=$5
x=$NF
gsub("[()]","",x)
IP=x
}

/^MAC Address/ {
MAC=$3
split($0,a,"(")
split(a[2],b,")")
VENDOR=b[1]
printf("%-16s| %-18s| %-35s| %-30s\n",IP,MAC,NAME,VENDOR)
}'

Here is an example of the output

[root@localhost ~]# ./discover 192.168.1.0/24
IP            | MAC               | NAME                               | VENDOR
192.168.1.1   | C8:D7:19:DE:54:2E | NyaRaePrimary                      | Cisco Consumer Products
192.168.1.100 | B8:27:EB:72:2A:4A | kodi1.grandenetworks.net           | Raspberry Pi Foundation
192.168.1.101 | 00:1F:3B:75:7F:EB | 192.168.1.101                      | Intel Corporate
192.168.1.102 | 6C:3B:E5:76:96:A5 | HP-Printer.grandenetworks.net      | Hewlett Packard
192.168.1.105 | A8:47:4A:AC:8F:89 | 192.168.1.105                      | Unknown
192.168.1.106 | F0:7D:68:0A:7C:8A | OllieMaeJoseph.grandenetworks.net  | D-Link
192.168.1.107 | 58:82:A8:81:C3:A6 | XboxOne                            | Unknown
192.168.1.109 | 28:56:5A:39:ED:FD | BRW28565A39EDFD.grandenetworks.net | Unknown
192.168.1.110 | 64:20:0C:90:24:D9 | Garlands-iPad.grandenetworks.net   | Apple
192.168.1.112 | 7C:D1:C3:17:0C:58 | Apple-TV.grandenetworks.net        | Apple
192.168.1.115 | B8:27:EB:12:DA:AC | kodi2.grandenetworks.net           | Raspberry Pi Foundation
192.168.1.118 | A4:77:33:8E:CE:C2 | Chromecast.grandenetworks.net      | Google
192.168.1.119 | 6C:AD:F8:5D:3A:D6 | 192.168.1.119                      | Azurewave Technologies
192.168.1.131 | F0:7D:68:0A:7A:D5 | EmmaEdwards.grandenetworks.net     | D-Link
192.168.1.135 | 28:10:7B:0C:3A:71 | EarlEdwards.grandenetworks.net     | D-Link International
192.168.1.136 | 00:09:B0:D6:A8:2A | 192.168.1.136                      | Onkyo
192.168.1.138 | 28:10:7B:0C:3A:74 | LeeJoseph.grandenetworks.net       | D-Link International
192.168.1.145 | D4:3D:7E:EF:93:99 | obama                              | Micro-Star Int'l Co
192.168.1.147 | E4:3E:D7:44:21:8F | LGwebOSTV.grandenetworks.net       | Unknown

Here is a Diagram of my home LAN as revealed by the Network Status Map in Nagios

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