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Top Forums UNIX for Beginners Questions & Answers ARP and Bonjour to build list of user devices Post 302993621 by Zooma on Sunday 12th of March 2017 10:00:21 AM
Old 03-12-2017
ARP and Bonjour to build list of user devices

Hi,
I want to build a list of the devices that are connected to my network and refresh that list every 10th minute (using an RPi with Raspbian). The host names are obtained by using Bonjour which is easily installed by:
Code:
sudo apt-get install libnss-mdns

To build the list manually, I do like this:

1. Find the broadcast address (I sometimes change subnet, so the address could change and the ARP table has to be refreshed at every run):
Code:
ip address show | grep eth0 | grep brd | awk '{print $4}'

2. Ping the broadcast address to build ARP table:
Code:
ping <broadcast address>

3. Print the desired fields of the ARP table:
Code:
arp -a | awk '{print $4 " " $1}'

This produces the desired output which would look something like this:
Code:
00:11:22:33:AA:BB iPhone1
00:11:22:33:AA:BC my Laptop
00:11:22:33:AA:BD ?
...

I want to make this process automated so that I get an updated list every 10th minute. Does someone know a good way of doing this? Have tried to script it but it seems I can't ping a stored IP address.

Cheers!
Sam
 

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arp(1M) 						  System Administration Commands						   arp(1M)

NAME
arp - address resolution display and control SYNOPSIS
arp hostname arp -a [-n] arp -d hostname arp -f filename arp -s hostname ether_address [temp] [pub] [trail] DESCRIPTION
The arp program displays and modifies the Internet-to-MAC address translation tables used by the address resolution protocol (see arp(7P)). With no flags, the program displays the current ARP entry for hostname. The host may be specified by name or by number, using Internet dot notation. OPTIONS
-a Display all of the current ARP entries. The definition for the flags in the table are: M Mapping; only used for the multicast entry for 224.0.0.0 P Publish; includes IP address for the machine and the addresses that have explicitly been added by the -s option. ARP will respond to ARP requests for this address. S Static; not learned for the ARP protocol. U Unresolved; waiting for ARP response. You can use the -n option with the -a option to disable the automatic numeric IP address-to-name translation. Use arp -an or arp -na to display numeric IP addresses. -d Delete an entry for the host called hostname. This option may only be used by the super-user. -f Read the file named filename and set multiple entries in the ARP tables. Entries in the file should be of the form: hostname MACaddress [temp] [pub] [trail] See the -s option for argument definitions. -s Create an ARP entry for the host called hostname with the MAC address MACaddress. For example, an Ethernet address is given as six hexadecimal bytes separated by colons. The entry will be permanent unless the word temp is given in the command. If the word pub is given, the entry will be published. For instance, this system will respond to ARP requests for hostname even though the hostname is not its own. The word trail indicates that trailer encapsulations may be sent to this host. arp -s can be used for a limited form of proxy ARP when a host on one of the directly attached networks is not physically present on the subnet. Another machine can then be configured to respond to ARP requests using arp -s. This is useful in certain SLIP configurations. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
ifconfig(1M), arp(7P), attributes(5) SunOS 5.10 7 Mar 2003 arp(1M)
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