Second exchange technology

Second exchange technology is development of relatively mature, switcher data link layer equipment, which can identify the MAC address information packets, according to the MAC address for forwarding, and use the MAC address and corresponding port records in their own internal an address list.

workflow

process

(1) when the switch from one port received a packet, it first read the source MAC address baotou, so it will know the source MAC address of machine is in on what port even;

(2) to go read the purpose of baotou, and MAC address in the address table lookup corresponding port;

(3) such as table has with this purpose MAC address the corresponding port, the packet directly copied to the ports;

(4) such as table can't find the corresponding port criterion packet radio to all ports, when purpose machine to source machine response, switches and can learn a purpose MAC address and what port, in our next transmit data correspond to all when they no longer need to broadcast port.

Constant circulation this process, the MAC address information for hyper all can learn, switcher is such establish and maintain its own address table.

principle

The working principle of from switcher below can infer three points:

(1) due to most port switches data and exchange, this requires the wide exchange bus bandwidth, if switcher have N a port, each port of bandwidth is M, switches bus bandwidth over N x M, then this switch can achieve wire-speed switching;

(2) study of port into the MAC address machine, address table size of address table (usually two kinds of means: one for BUFFER RAM, one for MAC table item number), address table size affect switches access capacity;

(3) another is commonly switcher specially used for handling the packet containing the specific ASIC (vehicle) chip apply, so done forwarding speed can be done very fast. Because each manufacturer directly affected by different, ASIC properties of product.

Above 3 tertiary layer switches also judge the main technical parameters of the performance quality, it please everyone in considering equipment selection carefully when comparison.

Routing technology

Routers in the OSI model work of layer 3 - the network layer operation, its working mode and second exchange similar, but routers in the third layer, work in this decide the difference between routing and switching in the passing packets use different control information, realizing the function of different ways. Working principle is the internal in router there is also a table, the table is marked if you want to a certain place, the next step should be to there go, if can find packets from routing table where to go next, the link layer information plus forwarding out; If you can't know the next step towards there, will this packet-discard, then return a message to the source address.

Routing technology essentially, however two functions: determine the optimal routing and forward packets. The routing table into all kinds of information, calculated by routing algorithm the best route to the destination address, then by relatively simple direct forwarding mechanism sends a packet. Accept data in accordance with the next router work on the same way forward, which in turn analogy, continued until the packet to the destination router.

Routing updates

Distance vector routing protocol

In all the dynamic routing protocol, the simplest is distance vector routing protocol (D - V). It is using the most simple Distance Vector Distance Vector, the abbreviation (-) routing algorithm V D.

Distance vector algorithm through the above methods, and accumulative network distance network topology information database. Distance vector protocols regular transmitted directly their all information routing tables to the neighbor (RIP agreement default is 30 seconds). The network from his neighbor routers router, and will get routing information along with their own these routing information local routing information sent to other neighbours, such pass on cadres to achieve hyper synchronous. Each router doesn't understand the whole network topology, they only know directly connected with their network, and according to the routing information obtained from neighbors routing table updates itself. It all the information by hearsay, it believes that all neighbor told all of its information, choose only in these neighbors the optimal to adopt, similar to the "message" this game.