Layer 2 ping

Linkloop is a piece of open source software which runs on Linux to test network connectivity over layer 2 (OSI : data link layer).

Linkloop is similar to ping, which operates at layer 3 (OSI network layer).

It’s a priceless tool when used to debug “network problems” in complex environments from the OS.

The linkloop application is also similar to the Cisco IOS command, pong. As a sidenote, pong is a useful command, because you can see response times in nanoseconds. Great for extreme/ultra low latency environments.

Pick interface on the same VLAN to listen on (target system)

# linkloop_reply eth2
Opening a socket on eth2
Received packet on eth2

Pick interface on same VLAN to send packets to (source system)

# linkloop -i eth1 -t 3 -n 5 00:50:56:11:22:33
Link connectivity to LAN station: 00:50:56:11:22:33 (HW addr 0x005056112233)
  -- OK -- 5 packets

OR :

  ** ROGUE RESPONDER: received from 0x005056112233
  ** ROGUE RESPONDER: received from 0x005056112233
  ** ROGUE RESPONDER: received from 0x005056112233
  ** ROGUE RESPONDER: received from 0x005056112233
  ** ROGUE RESPONDER: received from 0x005056112233

Further reading
http://linux.die.net/man/1/linkloop
http://linkloop.sourceforge.net/
http://docwiki.cisco.com/wiki/Cisco_Nexus_7000_Series_NX-OS_Troubleshooting_Guide_–_Troubleshooting_Tools_and_Methodology#Using_Pong

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