Test System Architecture designer must watch-Multicast

I. Data Transmission over an IP Network

Multicast technology is one of the three methods of data transmission over an IP network. Before introducing the IP multicast technology, we will give a brief introduction to the unicast, multicast, and broadcast modes of data transmission over an IP network:

GroupBroadcast

Unicast transmission: Implements point-to-point network connection between the sender and each receiver. If a sender transmits the same data to multiple receivers at the same time, multiple identical data packets must be copied accordingly. If a large number of hosts want to obtain the same copy of data packets, the sender will be heavily burdened, long delay, and network congestion. To ensure certain service quality, hardware and bandwidth need to be increased.

Multicast Transmission: Implements point-to-point network connection between the sender and each receiver. If a sender transmits the same data to multiple recipients at the same time, only one copy of the same data packet is required. It improves data transmission efficiency. This reduces the possibility of network congestion.

Broadcast Transmission: broadcasts packets in the IP subnet. All hosts in the subnet will receive these packets. Broadcast means that the network delivers a packet to each host in the subnet, whether or not these hosts are willing to receive the packet. Therefore, the broadcast scope is very small and only valid within the local subnet. Broadcast Transmission is controlled through routers and vswitch network devices.

Related Technologies

Ii. Multicast Technology

1. Architecture of IP multicast technology

The multicast protocol is divided into the group membership protocol between the host-router and the multicast routing protocol between the router-router. The Group Membership Protocol includes the IGMP (Internet Group Management Protocol ). Multicast Routing Protocols are classified into intra-domain multicast routing protocols and Inter-Domain multicast routing protocols. Intra-domain Multicast

GroupBroadcast

Routing Protocols include PIM-SM (Protocol Independent Multicast-Sparse Mode), PIM-DM (Protocol Independent Multicast-dense mode), dvmrp (Distance Vector Multicast Routing Protocol, inter-Domain multicast routing protocols include mbgp (Multiprotocol BGP) and msdp (Multicast Source Discovery Protocol. To effectively suppress the spread of multicast data on the link layer, two-layer multicast protocols, such as IGMP snooping and cGMP, were introduced.

IGMP establishes and maintains group membership information for the vro CIDR block. Based on the multicast group member information maintained by IGMP, the intra-domain multicast routing protocol uses a certain number of multicast routes.AlgorithmConstruct a multicast distribution tree to forward multicast data packets. The Inter-Domain Multicast Routing Protocol publishes routing information with multicast capabilities and Multicast Source Information between autonomous domains to forward multicast data across domains.

2. multicast IP Address

A Multicast IP address is used to identify an IP multicast group. Iana (Internet assigned number authority) allocates Class D address space to IP multicast, which ranges from 224.0.0.0 to 239.255.255. As shown in (binary representation), the first four digits of the IP multicast address are both 1110.

Octal group (1) octal group (2) octal group (3) octal group (4)

1110 XXXX XXXXXXXX

Multicast Groups can be permanent or temporary. Some of the multicast addresses are officially assigned. They are called permanent multicast addresses. What remains unchanged for a permanent multicast group is its IP address. The composition of its members can change. The number of members in a permanent multicast group can be arbitrary or even zero. IP addresses that are not reserved for permanent multicast groups can be used by temporary multicast groups.

224.0.0.0 ~ 224.0.0.255 is the reserved multicast address (Permanent Group address). The address 224.0.0.0 is retained without allocation. Other addresses are used by the routing protocol. 224.0.1.0 ~ 238.00000000255 is the user's available multicast address (temporary group address), which is valid across the network; 239.0.0.0 ~ 239.00000000255 is the multicast address of the Local Management Group. It is valid only for a specific local range. The list of Common Reserved multicast addresses is as follows:

224.0.0.0 base address (retained) 224.0.0.1 addresses of all hosts 224.0.0.2 addresses of all multicast routers

224.0.0.3 not allocated 224.0.0.4 dvmrp router 224.0.0.5 OSPF Router

224.0.0.6 OSPF Dr 224.0.0.7 st router 224.0.0.8 st host

224.0.0.9 rip-2 vro 224.0.0.10 the active proxy of the OSPF vro 224.0.0.11

224.0.0.12 DHCP server/relay proxy 224.0.0.13 all PIM Routers

224.0.0.14 RSVP encapsulation 224.0.0.15 all CBT routers 224.0.0.16 specify SBM

224.0.0.17 all sbms 224.0.0.18 vrrp

3. Group member protocol (IGMP)

The IGMP protocol runs between the host and the multicast router directly connected to the host. The host uses this Protocol to tell the local router to join and accept information about a specific multicast group, at the same time, the router periodically queries whether a member of a known group in the LAN is active (that is, whether the CIDR block still belongs to a multicast group) through this protocol ), allows you to collect and maintain group members on the connected network.

IGMP has three versions. igmpv1 is defined by rfc1112. Currently, igmpv2 is commonly used and is defined by rfc2236. IGMPv3 is still a draft. Igmpv1 defines the basic process of querying and reporting group members. igmpv2 adds a mechanism for members to leave quickly, the main function added in IGMPv3 is that a member can specify to receive or not to receive packets from some multicast sources. This section describes the functions of the igmpv2 protocol.

Igmpv2 uses the queryer election mechanism as the only queryer for the connected CIDR Block election. The queryer periodically sends a universal group query message to query the member relationship. The host sends a report message to respond to the query. When you want to join a multicast group, the host does not have to wait for the query message to actively send the report message. When you want to leave a multicast group, the host sends an exit group message. After receiving the exit group message, the queryer sends a query message for a specific group to determine whether all group members have left.

Through the above IGMP mechanism, a table is created in the multicast router, which contains the vro ports and the group members in the subnet corresponding to the port. When a vro receives a data packet from a group of G, it only forwards the data packet to the ports with G members. The routing protocol determines how data packets are forwarded between routers. The IGMP protocol is not responsible.

4. layer-2 multicast protocols

Layer-2 multicast protocols include IGMP snooping, IGMP proxy, and cGMP.

The implementation mechanism of IGMP snooping is that the switch listens to IGMP members of the router to report messages, forming a correspondence between group members and switch interfaces; based on this relationship, the vswitch transfers multicast packets to APIs with group members only.

IGMP proxy and IGMP snooping have the same functions but different mechanisms: IGMP snooping only obtains relevant information by listening to IGMP messages, the IGMP proxy intercepts the IGMP request of the end user and then forwards it to the upper-layer router.

CGMP (Cisco Group Management Protocol) is a private protocol developed by Cisco Based on Client/Server models. With the support of cGMP, the multicast router can notify the vswitch when the host is added to or removed from the multicast group based on the received IGMP data packets. The vswitch uses the forwarding table constructed by the information to determine which interfaces the multicast data packets are forwarded. Gmrp is the standard protocol between the host and the Ethernet switch. It enables multicast users to register multicast members on the second-layer switch.

5. Multicast Routing Protocol (PIM-SM)

Among the many multicast routing protocols, the most widely used protocol is PIM-SM Sparse Mode protocol-Independent Multicast.

In the PIM-SM domain, routers running the PIM-SM protocol periodically send HELLO messages to identify the adjacent PIM router and are responsible for election of the specified router (DR) in the multi-access network. Here, Dr is responsible for sending "Add/cut" messages to the direct connection group members in the direction of the multicast distribution tree root node, or sending the data from the direct connection group source to the multicast distribution tree.

Addressing

Class A 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

Class D 224.0.0.0-239.255.255.255

A, B, and C class IP packet forwarding are based on the destination IP address. Class D (multicast address) packet forwarding is based on the source address.

Classification of multicast addresses:

Retain -- 224.0.0.0-224.0.0.255

User Group broadcast address -- 224.0.1.0-238.255.255.255

Local Management Group -- 239.0.0.0-239.255.255.255 (for private multicast domains, similar to private IP addresses)

RPF:

A multicast packet has ed on an interface will be accepted if your ed on the interface that wocould be used to send a unicast IP packet back to the source; this is called reverse path Forwarding (RPF ).

Reverse route forwarding:

After the device receives a multicast packet on the interface, if the unicast route to the multicast source is also learned from this interface, the multicast data will be forwarded; otherwise, the multicast data will be discarded.

Problems to be Solved by Multicast technology:

Currently, multicast technology has many unsolved problems, such as Multicast Security, multicast congestion control, multicast status aggregation, and multicast traffic fee.