IP Multicasting

IP multicasting is the multicast hardware abstraction, is a standard IP network layer protocol extensions. It does this by using a specific IP multicast address, delivered in accordance with the principle of maximum, the IP datagram transmission to a multicast group (multicast group) set of host. Its basic approach is: When an individual to a group of people to send data, it does not have data to send data to everyone, simply send data to a specific address group booking, all add to the group's per capita You can receive the data. So the sender, the data can be sent only once to send to all recipients, greatly reducing the network load and the burden of the sender. 1. Concept: Is the need to receive multicast traffic sent by the client that a set of data, is a harmless radio. 2 advantages: Does not affect the data does not receive the multicast host, can save network bandwidth, reducing the host processing burden. 3. Multicast address: 224.0.0.0 - 239.255.255.255, not as unicast ip segment as a broadcast address and network address of the divided. Specific :224.0.0.0 - 224 .0.0.255 local reservations, to use well-known protocol, ttl = 1. 224.0.0.1 is the host which receives all Ben Wang, 224.0.0.2 is all routers receive the Ben Wang. 239.0.0.0 - 239.255.255.255 private multicast address. 232.0.0.0 - 232.255.255.255 source-specific multicast. 4. Multicast MAC address structure: 01005E, fixed hex bit, followed by a fixed bit 0, then any of their after. ip and mac mapping, for example: ip address 229.147.109.235 Divided into bit 11100101.1 / 0010011.01101101.11101011 Multicast mac structure 01005E "0" / ..........( 23 after the slash correspond with the above) Obtained: 01005E136DEB to ip229.147.109.235 corresponding multicast mac address. We can see from the example of 32 Multicast address mapping to a mac address, so the deployment of measures to open when a network using the ip multicast address (change the tail) 5. Multicast distribution tree and shared distribution of the source tree Source distribution tree to ensure that the purpose of the shortest path to reach the source, but for each multicast source to maintain a tree, CPU usage rate. Shared distribution tree to choose RP, RP recently to ensure the purpose, not for each source to maintain a tree, while maintaining a common root in the tree to the RP, so saving equipment resources, but can not guarantee to Recently a source path. (Rp source sent to the multicast to unicast ip in ip form) 6.RPF (Reverse Path Forwarding) RPF check principle: router unicast routing table to find the source address to determine whether the interface the packet arrives back at the source of the reverse path, if the RPF check is successful, if not marked "RPF failure discarded" and discard the packet. Is simply the data according to the routing table entry to check the back of the package, determine to go back on the line. Role: For multicast, to prevent loops (multicast RPF check is enabled by default and can not be closed); for unicast, prevents IP spoofing attacks (need to manually configure RPF checks)