Ethernet

Hi, A quick question on ethernet. I just ran ethereal for a minute or so on my Ethernet IP network. All messages originate from IP addresses 192.168.210.xxx which i would expect but the destination address for each packet according to ethereal is 239.XXX.XXX.XXX. I have no IPs of this address that I know of on the network. Any ideas. Regards Alan Case

Its the multi-cast version of a 10.x.x.x or 192.168.x.x (both uni-cast).

Read more here:
http://www.sprintlink.net/multicast/addresses.html

Why you're seeing it on your network is beyond me...

I'll bet you're running EtherNet/IP I/O connections or Produced/Consumed tags between ControlLogix processors.

I've seen the same multicast addresses when sniffing EtherNet/IP networks and that sent me scrambling for the TCP/IP networking reference books.

There is a good summary of how IP multicast is used in EtherNet/IP in the Rockwell Knowledgebase: Document A46234811

Thanks Ken. You are correct and that document explains what I am seeing. Regards Alan Case

Has anyone out there had success containing the multicast traffic using VLANs? I believe that the traffic from ports that do not support VLANS propagates from VLAN to VLAN.