Posts tagged ip

arping: duplicate ip address detection

posted on 2016-03-31 22:50

Duplicate IP's within your subnet are a problem that you can detect via arping. It sends a layer2 ARP REQUEST to detect if an IP is already known within the network.

Usually only this is sufficient for usage from the shell:

arping -D <IP>`

When you simply receive a response on the commandline, the IP is in use already. If you use vlans, you have to specify your interface with -I, too.

If you want to use this from within scripts, you might want this:

arping -D -w2 -c2 -I <INTERFACE> <IP>
echo $?

arping returns zero if there's exists a duplicate IP.

One thing to keep in mind is that some linux distributions have several packages available, but only one it the arping. See on debian, for example, you got these two on jessie:

arping/stable 2.14-1 amd64
  sends IP and/or ARP pings (to the MAC address)

iputils-arping/stable,now 3:20121221-5+b2 amd64 [installed]
  Tool to send ICMP echo requests to an ARP address

You need the iputils-arping one, if you happen to use debian.

IP over serial connection / RS232 via SLIP

posted on 2015-10-10 03:31:04

As of 2015, this is very likely stuff which is needed anymore. Still, for documentation reasons:

slattach /dev/ttyUSB0 -p slip -s 9600 -dL &
# interface 'sl0' just got created now
ifconfig sl0 <IP>

Repeat this on the other host, and you should be able to send ping over your serial connection.

ip commands in linux

posted on 2014-06-23 17:28:11

The currently usually used tools and which ones will succeed these:

Purpose                        | Legacy net-tools | iproute2
-------------------------------+------------------+-----------------
Address and link configuration | ifconfig         | ip addr, ip link
Routing tables                 | route            | ip route
Neighbors                      | arp              | ip neigh
VLAN                           | vconfig          | ip link
Tunnels                        | iptunnel         | ip tunnel
Multicast                      | ipmaddr          | ip maddr
Statistics                     | netstat          | ss

Obtain your external ip while being on the shell

posted on 2013-11-16 00:42:42

Before you use google and a web browser, just use:

curl ifconfig.me

Easy. For more options go to ifconfig.me.

UPDATE:

curl ipecho.net/plain;echo

is way faster.

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