![]() If this bit is set, the MAC frame is destined either for an arbitrary group of hosts or all hosts on the network (if the MAC destination address is the broadcast address ). As shown in below figure, Bit 0 of Octet 0 in an IEEE MAC address indicates whether the destination address is a broadcast/multicast address or a unicast address. The IEEE 802.2 specification makes provisions for the transmission of broadcast and multicast packets. This results in IP multicast addresses spanning a range from 224.0.0.0 through 239.255.255.255. Addresses in this space are denoted with a binary “1110” prefix in the first four bits of the first octet, as shown in below figure. The second thing need to note is how multicast destination MAC address derived from a multicast IP address.IP multicast addresses have been assigned to Class “D” address space by the Internet Assigned Number Authority (IANA). They use mDNS (224.0.0.251) group address for that. In my environment I had iPad3 with AppleTV. I think Apple is using certain of these group address discover certain services within local subnet. (Ref ) These local network multicast packet go with TTL=1 & therefore cannot go beyond local subnet. Multicast Address range 224.0.0.0/24 is allocated for “Local Network Control” 224.0.1.0/24 ” is for “Internetwork Control” by IANA. Usually these are top end of addresses in a given class B & better to avoid it using for your application group addresses.Ģ39.255.255.255 – SAP (Session Announcement Protocol)Ģ39.255.255.251 – Multicast Discovery of DNS ServicesĢ39.195.255.255 – SAP (Session Announcement Protocol)Ģ39.195.255.251 – Multicast Discovery of DNS Services Since I have used SAP for my multicast stream session announcement, these group addresses shown in my wireless network. When I search these group addresses on web, I found that certain private multicast (239.x.x.x) group addresses used for specific applications. But when I monitor multicast on my controller I have noticed lot of other multicast group addresses listed there(see below). During my “VideoStream” testing I have used 239.255.255.200 group address for my video stream. When I did multicast testing on my wireless network last couple of days I noticed few things may worth to note here.įirst thing is the group addresses used by different services which we may not aware of.
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