![]() ![]() ![]() I could have explained this above but then you would have skipped through this part which does make a difference. Last 7 bits of 64 which still equals 64 converted to binary = 1000000Īfter removing 1 bit from our binary result it still equals 64 so this is what we will be using in the next step. Since we are only using the last 7 bits from the second octet, just drop the first 0 or 1 from our binary number (first binary number on the left, the result from 128 above). So above we converted the second octet of our multicast IP which was 64 to decimal which equal 01000000. You keep doing this until you can no longer subtract from the octet and you have converted decimal to binary. ![]() Can 64 be subtracted from 64? Yes, write a 1. Can 128 be subtracted from 64? No, write a 0. A quick way to do this is by following this example below. In the example I will be using the second octet of the multicast IP 239.64.100.1 which would be 64. The first step is to convert the second octet of the multicast IP to binary. You should have a good understanding of IP sub-netting or this may get a bit confusing.Ĭonvert Second Octet of Multicast IP to Binary To determine the rest of the MAC address we will use the remaining 23 low order bits to generate the full MAC address. The high order 25 bits of the MAC address are fixed and that is the 01-00-5E. As I explained above, any MAC address you see that starts with 01-00-5E is related to a multicast address. There is a specific range assigned for multicast, 01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF for Ethernet and Fiber Distributed Data Interface (FDDI). I’ll explain below exactly how to determine the multicast MAC address from the multicast IP as well as provide a few helpful websites.Īt the layer 2 level whenever multicast is used it has to be assigned a MAC address in order to work. I knew that any mac address that started with 01-00-5E was a multicast address, but wasn’t sure how the rest of it was calculated. (With a switch you would only see Broadcasts or communication between CPU and your Sniffing PC)įurtheryou will need any communication initiated from or to CPU, so that there´s traffic that you can sniff.Recently I was working to track down a multicast problem for a client on an enterprise network and needed to determine what the exact multicast MAC address would be. Or try to use an ethernet sniffer like wireshark.īut use a Hub Device (not a switch) for sniffing, you then are able to see both - MAC Adress and IP Adress. Step 7 tries to connect to the PLC using ISO protocol, and displays infos of your CP343-1. I think that should work, when you connect to the subnet with any ip-adress. So you could use Step 7 Function target-system - edit ethernet device. You see - thatsmore complex, you need to know mor about IP Adresses and IP subnetting.īuti can imagine what you want - handle a CPU although you don´t have infos or S7-Project! Try it with a Windows XP System with Internet connection These are services for converting MAC Adresses to IP Adresses RARP and IP Adresses to MAC Adresses ARP in an subnet. Or actual RARP (Reverse Adress Resolution Protocol) The service you need is called ARP (Adress Resolution Protocol) You´re able to assign any IP Adress to an ethernet device.īut you should use Private IP Adresses from the Pool of Private Class A (10.0.0.0|8) or Private Class C IP Adresses (192.168.0.0|24) So I´m afraidthere´s no way to CALCULATE an ip adress from mac adress or reverse!Įvery Ethernet device should have a worldwide unique MAC Adress. What if I dont know IP address of CPU315 or CP341 card ![]()
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