Multicast transfer: the sender and receiver between each realize point-to-multipoint network connections. If a sender while giving multiple recipients of transmission the same data, also need a copy of the same packets. It raises the data transmission efficiency. Reduce the backbone network appear congestion of possibilities.
A, IP network data transmission
Multicast technology is IP network data transmission in one of three ways, introduce IP multicast technology, before to IP network data transmission unicast and multicast and broadcast way to do a simple introduction:
Unicast transfer: the sender and receiver realizing each point-to-point network connections. If a sender while giving multiple recipients of the same data transmission, must also corresponding copying multiple copies of the same packets. If there is a lot of the same host hopes to get a packet, copy will lead to the sender burden is heavy, delay long, network congestion, To guarantee the quality of service should be increased to hardware and bandwidth.
Multicast transfer: the sender and receiver between each realize point-to-multipoint network connections. If a sender while giving multiple recipients of transmission the same data, also need a copy of the same packets. It raises the data transmission efficiency. Reduce the backbone network appear congestion of possibilities.
Broadcasting transmission: refers to the IP subnetting within packets, all in radio subnet internal host will receive these packets. Radio means network to subnet every hosts are delivered a packet, no matter whether the host to receive this packet. So broadcast use scope is very small, only in local subnet valid, by routers and network equipment control radio transmission.
Second, multicast related technologies
1, IP multicast technology system structure
Multicast protocols are divided into host - router between members relationship agreement and router - router between the multicast routing protocol. Group relationship agreement includes IGMP (Internet group management protocol). Multicast routing protocol is divided into domain of multicast routing protocols and domain between multicast routing protocol. Domain Multicast Routing protocols including PIM - SM (Protocol Independent Multicast - Sparse Mode), PIM - DM (Protocol Independent Multicast - Dense Mode), DVMRP (Distance Vector Protocol) such as Multicast ccna agreement, domain of Multicast Routing protocols including between MBGP (Multiprotocol BGP), MSDP (" Discovery Protocol) returned Multicast protocols. At the same time in order to effectively restrain multicast data on link layer diffusion, introduced IGMP Snooping, CGMP etc layer multicast protocols.
IGMP to establish and maintain the router straight segment of the group relation network information. Domain multicast routing protocol IGMP maintenance according to these multicast group relations information, the use of certain multicast routing algorithm tectonic multicast distribution of multicast tree on the packet. Domain of multicast routing protocols in between the autonomous domain has issued a multicast ability between the routing information and multicast source information for multicast data in domain between the forwarding.
2, the multicast IP address
Multicast IP address used to identify an IP multicast group. IANA (assigned by the authority) Internet address space allocated to the class D IP multicast, ranging from 224.0.0.0 to 239.255.255.255. Shown below (binary representation), IP multicast address top four are for 1110.
Octet in (1) eight group (2) eight group (3) eight group (4)
1110XXXX XXXXXXXX XXXXXXXX XXXXXXXX
Multicast group can be permanent can also be temporary. Multicast group address some of the distribution by the official, called the permanent multicast group. Permanent multicast group to remain the same is its IP address, group members of the composition can change. Permanent multicast group members of the quantity can be arbitrarily, can even to zero. Those not retained for permanent multicast group to use IP multicast address, can be temporary multicast group to use.
224.0.0.0 ~ 224.0.0.255 to reserve the multicast address (permanent group address), address 224.0.0.0 reserves don't do distribution, other address for routing protocol used; 224.0.1.0 ~ 238.255.255.255 for the multicast address users can (temporary group address), network-wide security effective; 239.0.0.0 ~ 239.255.255.255 for local management multicast addresses, only in the specific local scope effective. Common reserve the multicast address listed below:
224.0.0.0 benchmark address (reserves)
224.0.0.1 all host address
224.0.0.2 all multicast router's address
224.0.0.3 not allocation
224.0.0.4 Distance Vector DVMRP (Multicast ccna Protocol, Distance Vector of Multicast Routing Protocol) router
Shortest Path 224.0.0.5 ospf (Open First, Open Shortest Path is preferred) router
Dr Designated Router (224.0.0.6 ospf Designated Router),
224.0.0.7 st (Shared Tree, sharing Tree) router
224.0.0.8 st host
224.0.0.9 rip - 2 router
224.0.0.10 Eigrp (Gateway Protocol, Interior ccna to enhance Gateway Interior Routing lines Protocol) router 224.0.0.11 activities agent
224.0.0.12 DHCP server/relay agent
224.0.0.13 all pim (Protocol Independent Multicast, agreement irrelevant Multicast) router
224.0.0.14 RSVP (Protocol, Resource Reservation Resource reserve agreement) encapsulation
224.0.0.15 all CBT router
224.0.0.16 specified Bandwidth Management, Subnetwork SBM (subnet Bandwidth Management)
224.0.0.17 all SBMS
224.0.0.18 VRRP insgroupsto Router Protocol Redundancy, Virtual Router Redundancy Protocol)
3, group relationship protocol (IGMP)
IGMP protocol running on host and with mainframe directly connected multicast router, through this agreement between hosts told local router hope to join and accept a particular multicast group information, and at the same time router through this agreement periodically inquires the wlan a known group members are in active state (namely the network segment if there's still belong to a multicast group members), to achieve even network group relationship of collecting and maintenance.
There are three IGMPv1 IGMP version, by definition, RFC1112 gm now is, by definition IGMPv2 RFC2236. IGMPv3 is still a draft. IGMPv1 defined the basic group query and reporting process, IGMPv2 based on this added group quickly leave mechanism, IGMPv3 add's main function is to members can be specified to accept or designated don't accept certain multicast source message. Here introduced emphatically IGMPv2 agreement function.
IGMPv2 through inquires the device for election mechanism linking section election only inquires the device. Inquires cyclical send universal device group members relationship inquires query message, Machine to send report news to reply query. When wanting to join a multicast group, the host needn't wait inquires, active send a report news news. When leaving a multicast group, the machine to send leave group messaging, Received left group news, inquires the editor sent specific groups to determine whether all query news groups have left.
Through the above IGMP mechanism, the multicast router inside establish a list, including routers in the port of each port and corresponding subnet what are the group members. When a router to receive a group G data message, only to those who have G members of the port forwarding data message. As for data message on a router between how forwarding criterion by routing protocol decision, IGMP protocol is not responsible for.
4, network layer multicast relevant agreement
The network layer multicast relevant agreement includes IGMP Snooping, IGMP existent and CGMP agreement.
The realization of the IGMP Snooping mechanism is: switches through to the router protected reliably against detective host hair IGMP members report news way, forming group and the switch interface corresponding relationships, Switches according to the corresponding relationship will receive multicast packet only to have group interface.
IGMP existent IGMP Snooping function with the same but mechanism are motiva ted: IGMP Snooping just by the news of protected reliably against detective IGMP to obtain relevant information, and is the IGMP existent intercept the end-user IGMP request and relative processing, it can be transmitted to the upper router.
CGMP (Group Management Protocol) is Cisco Cisco based on client/server model development of private agreement, the CGMP, under the support of multicast router according to receiving notice IGMP packet switch which hosts when join a multicast Group and out by these information, switches use this turn published to determine what will multicast packet forwarding to interface. GMRP is host to Ethernet switches the standard protocol, it makes the multicast users can layer 2 switches on multicast members to register.
5 and multicast routing protocol (PIM SM) -
Numerous multicast routing protocol, and currently applied the most protocol is PIM - SM sparse model agreement irrelevant multicast. In SM domain and operation - PIM PIM - SM agreement router periodically send Hello message, to find the adjacency of PIM router, and in charge of multi-channel access network in a designated router (DR) election. Here, DR responsible for its direct link group towards multicast distribution root node direction send "add/pruning" the message, or will be connected directly multicast source data sent to multicast distribution tree.
Plait addresses
A kind of 0.0.0.0-127.255.255.255
Class B 128.0.0.0-191.255.255.255
Class C 192.0.0.0-223.255.255.255
D class 224.0.0.0-239.255.255.255
A, B, C IP packet forwarding based on destination IP address. D class (multicast addresses) packet forwarding based on source address.
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