doc for arp_sweep aux scanner discovery mod rapid7#8296

Author: renpic

documentation/modules/auxiliary/scanner/discovery/arp_sweep.md

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+## Vulnerable Application
+
+  ARP (the Address Resolution Protocol) is a companion protocol to IPv4.
+  Its purpose is to resolve internet layer addresses (as IPv4) of stations
+  on the local network to their corresponding link layer addresses
+  (for example, Ethernet).
+
+  (As a side note, in IPv6 this task is assolved by the Neighbour Discovery
+  protocol.)
+
+  The discovery is limited to the broadcast domain of the local network;
+  so you cannot discover hosts that aren't directly connected to your LAN.
+
+## Target Devices
+
+  All the devices on a network should reply to ARP requests for communication
+  and duplicate address detection, so usually every device should be
+  discoverable.
+
+## Verification Steps
+
+  Here we suppose the local network is 192.168.0.0/24:
+
+  1. Start msfconsole
+  2. Do `use auxiliary/scanner/discovery/arp_sweep`
+  3. Set the RHOSTS according to your local network. For example, on a
+     192.168.0.0/24 network:
+     `set rhosts 192.168.0.0/24`
+  4. Do `run`
+
+## Scenarios
+
+  An example output on a home network:
+  ```
+    msf > use auxiliary/scanner/discovery/arp_sweep
+    msf auxiliary(arp_sweep) > set RHOSTS 192.168.0.0/24
+    RHOSTS => 192.168.0.0/24
+    msf auxiliary(arp_sweep) > run
+    
+    [*] 192.168.0.1 appears to be up (D-Link International).
+    [*] 192.168.0.2 appears to be up (UNKNOWN).
+    [*] 192.168.0.4 appears to be up (ASUSTek COMPUTER INC.).
+    [*] Scanned 256 of 256 hosts (100% complete)
+    [*] Auxiliary module execution completed
+  ```