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Posted by Mark on May 12, 2009, 5:14 am
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studying multicasting and IGMP specifically, and have a few points I don't clearly understand. First of all why do we need Ethernet multicast addresses, wouldn't IP multicasting suffice to distribure traffic among the groups of hosts? I only guess, there are protocols exploiting Ethernet-based multicasting? And the second. From RFC1112: "IP host address is mapped to Ethernet multicast address by placing the low-order 23-bits of the IP address into the low-order 23 bits of Ethernet multicast address 01-00-5e-00-00-00". Does this mean that in order to send a multicast packet, a host must supply a properly built MAC address in the form defined above, in its Ethernet header field (destination address)? So the OUI, purchased by equipment manufacturers would not suffice? Thanks. -- Mark | |||||||||||||
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Posted by glen herrmannsfeldt on May 12, 2009, 5:17 am
Please log in for more thread options If the IP packet goes over ethernet, it needs an ethernet multicast address to be multicast. > And the second. From RFC1112: "IP host address is mapped to Ethernet
> multicast address by placing the low-order 23-bits of the IP address into > the low-order 23 bits of Ethernet multicast address 01-00-5e-00-00-00". > Does this mean that in order to send a multicast packet, a host must supply
> a properly built MAC address in the form defined above, in its Ethernet > header field (destination address)? So the OUI, purchased by equipment > manufacturers would not suffice? Yes. -- glen | |||||||||||||
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Posted by pxcdan on May 13, 2009, 8:18 am
Please log in for more thread options > Hello
t
> > studying multicasting and IGMP specifically, and have a few points I don'= > clearly understand. First of all why do we need Ethernet multicast
he
> addresses, wouldn't IP multicasting suffice to distribure traffic among t= > groups of hosts? I only guess, there are protocols exploiting Ethernet-ba=
sed
> multicasting?
Layer 2 devices within the network would be unable to handle IP-only multicast addressing. Multicasting is used in a popular industrial control protocol called Ethernet/IP (the IP here stands for industrial protocol); the infrastructure devices on these control networks are almost exclusively L2 switches. | |||||||||||||
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> clearly understand. First of all why do we need Ethernet multicast
> addresses, wouldn't IP multicasting suffice to distribure traffic among the
> groups of hosts? I only guess, there are protocols exploiting Ethernet-based
> multicasting?