Interpreting several important features of layer-3 Exchange Technology

In today's developed information society, there are many problems to be solved by the layer-3 Exchange Technology. So far, the maximum processing capacity of the most advanced switch is more than 10 million packets per second, this is far worse than some large routers.

In a switching network, especially a large-scale switching network, it is unimaginable to have no routing function. However, the processing capability of the router limits the speed of the switching network, which is the problem to be solved by layer-3 switching. Layer-3 switches do not spread broadcast packets like other layer-2 switches. layer-3 switches are called layer-3 switches because they can understand layer-3 information, such as IP addresses and ARP.

Therefore, a layer-3 switch can understand the purpose of a broadcast packet, and meet the needs of the people who send the broadcast packet without spreading it out, (whether they are in any subnet ). If the layer-3 switch is a router, it should also be called a super-high-speed anti-traditional router, because the layer-3 switch does not perform any "split" data packets, all packets passing by will not be modified and will be transferred to the destination at the exchange speed.

At present, there is still a long way to mature layer-3 switches. Like some other new technologies, it is still necessary to standardize their protocols. At present, many manufacturers claim to have developed third-tier switches. However, they have been tested by international authorities with different practices and different performance.

In addition, it may be based on the strategy of various manufacturers occupying the market. Currently, layer-3 switches can exchange routing IP addresses/IPX protocols, and cannot handle other dedicated protocols with certain application fields. Therefore, relevant experts believe that layer-3 exchange technology will be the main network integration technology in the future.

Traditional routers will be applied within a period of time, but they will be in the edge of the network, wan interconnection, security control (firewall), and heterogeneous network interconnection with dedicated protocols with limited processing speed.

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Technical Features of layer-3 Switching

1. Line rate routing:

Compared with traditional routers, the routing speed of layer-3 switches is generally 10 times faster or dozens of times faster, enabling line rate routing forwarding. Traditional routers use software to maintain the route table, while layer-3 switches use ASIC Application Specific Integrated Circuit) hardware to maintain the route table, so as to achieve line-rate routing.

2. IP routing:

On a LAN, a layer-2 switch identifies the packet sender through the source MAC address and forwards the packet according to the destination MAC address. For a data packet whose destination address is not on the local area network, a layer-2 switch cannot directly send it to the destination. It must be forwarded through a routing device such as a traditional router, connect the vswitch to the routing device.

If you set the default gateway of A vswitch as the IP address of the router device, the vswitch sends the packet to be forwarded by the route device. The routing device checks the destination address of the data packet and its route table. If the route table finds the forwarding path, the routing device forwards the data packet to other network segments. Otherwise, the data packet is discarded.

Vro is expensive, complex, and slow. It is easy to become a network bottleneck because it needs to analyze all broadcast packets and forward some of them, and exchange route information with other vrouters, and these processing processes are all handled by the CPU rather than the dedicated ASIC), so the speed is slow.

A layer-3 Switch identifies a packet forwarding through a MAC address like a layer-2 switch, and also performs route forwarding between two CIDR blocks as a traditional router. In addition, the layer-3 switch can implement line rate routing because it uses a dedicated chip to process route forwarding.

3. Routing

Compared with traditional vrouters, layer-3 vswitches are not only fast but also easy to configure. In the simplest case, when the layer-3 switch enables the automatic discovery function by default), once the switch is connected to the network, you only need to set the VLAN.

Set a route interface for each VLAN. The layer-3 switch automatically limits the data stream in the subnet to the subnet, and implements Packet Exchange Between subnets through routing. The administrator can also manually configure the routing mode: Set a port-based VLAN, and assign an IP address and subnet mask to each VLAN to generate a routing interface. Then, manually set the static route or start the dynamic routing protocol.

4. route protocol support:

The layer-3 switching technology can use the automatic discovery function to process the forwarding of local IP packets and learn the addresses of neighboring routers. It can also use the dynamic routing protocols RIP1, RIP2, and OSPF to calculate the routing path. The following describes the RIP and OSPF protocols.

Routing Information Protocol (RIP) is an Internal Gateway Protocol (IGP). It is mainly used in medium-scale networks. The RIP protocol uses the Distance Vector Algorithm and includes the route information to reach the destination IP vector) ), the path with the minimum number of hops is the optimal path.

The maximum number of hops allowed by RIP is 15. The destination address that requires 16 or more hops is considered inaccessible. The RIP Router exchanges route information with the neighboring RIP Router through periodic broadcast. The broadcast interval can be set. The broadcast content is the entire route table.

When the RIP Router receives the route table of the neighboring router, it determines whether to update its route table after calculation. If your route table needs to be updated, the router sends the updated content to the neighboring router immediately after the update is completed without waiting for the end of the broadcast interval.