L2 switch belongs to the data link layer, it can automatically identify the MAC address in the packet and forward based on the MAC address. Meanwhile, it records the MAC address with the corresponding port in its internal address table. The main process is as follows:

1. When a switch receives a packet from a port, it reads the source MAC address in the header, so that it knows where the machine is connected to the source MAC address.

2. Read the destination MAC address in the header and look for the corresponding port in the address table.

3. If there is a corresponding port to the destination MAC address, the packet is copied directly to this port.

4. If can't find the corresponding ports in the table, the packet will be broadcast to all ports, when the purpose machine responds to the source machine, the switch can learn and record the destination MAC address and corresponding port, it is no longer need to broadcast to all ports when transmitting data in the next time.

Through the above process, the l2 switch sets up and maintains its address table, then records and learns the MAC address of the whole network system.

The following three points can be inferred from the working principle of the l2 switch:

1. Due to the switch exchanging data for the number of ports at the same time, it requires a wide exchange bandwidth, if there is an N-port l2 switch, the bandwidth of each port is M, therefore total bandwidth is more than N*M, then the switch can achieve wire-speed switching.

2. Learning the MAC address of the connected machine, writing into the address table, recording the address table size (generally two kinds of representation: one is BEFFER RAM, the other one is for the value of MAC table), the address table size affects switch’s access capacity.

3. ASIC Chip(Application-specific Integrated Circuit) is commonly used in a l2 switch, which is dedicated to processing packets, so the forward speed can be very fast. However, each manufacturer adopts a different ASIC model, which affects product performance directly. The ONV (Model: ONV-POE38036PFM) adopts the import stability aerospace grade chip, and the product performance is self-evident.

The above three points are also the main technical parameters to judge the performance of l2 and l3 switches, so please pay attention to the comparison when selecting products.

Routing Technology

The router is working on the third layer in OSI, which is the network layer. Its working mode is similar to the l2 switch. But working on the network layer, it determines that routers and switches use different control information when transmitting packets, and different ways of implementing functionality. The working theory is that there is a table in the interior of a router, which is marked to guide the data to the destination. If there is a known destination for a packet in the routing table, the packet would be forwarded with link layer information. But if there isn’t a known destination, then the router would lose the packet and feedback a message to the source address.

Routing technology virtually contains just 2 functions: Selecting the best route and data-packing forward. Different information will be recorded in the routing table and the best path of destination by router algorithm. After that, the data package will be sent directly by a simple forwarding mode. Meanwhile, the next router works in the same way till the date-package loading in the destination as a result. 

There are also 2 ways of maintenance for the router table, One is the update of router information which releases partial information or entire information. The routers master the topological structure of the whole network by learning from each other. This kind of routing protocol was named distance routing protocol, But another one has broadcast itself link status and masters the whole network’s routing information to get the best-transmitting path. It was called link-status routing protocol. 

The router has to make lots of path calculations. Therefore the working capability was decided by the CPU.

For sure. This judgment is just for middle or low routers since high-end routers usually use distributed processing systems as their design.

Layer 3 Switching Technology

What is l3 switching technology? In short, it is the combination of l2 switching technology and l3 forwarding technology. After it solves the network segmentation of LAN, it must rely on the router to manage for subnet in the network. And it solves the network key point caused by the low speed and complexity of the traditional router. Here is a simple network to show the working process of a l3 switch.

A Simple Networking

Equipment A with IP—L3 switch—Equipment B with IP

If there is data from A to B. And the destination IP is known. Then it gets the network address through the subnet mask for A, and checks if the destination IP is in the same network segment.

If it is in the same network segment, but users don’t know the MAC address that need to forward the data to, then users can send an ARP request by A, and B will feedback on its MAC address. After that A uses this MAC to encapsulate the packet and send it to the switch. The switch would start with the l2 switching module, look up the MAC address table, and forward the packet to the corresponding port.

If it is not in the same network segment, to achieve communication between A and B, it forwards the first normal packet to a default gateway without the corresponding MAC address in the flow cache. The default gateway has been set in the operating system and corresponds with the l3 routing module. Therefore, the first record in the MAC table is the MAC address of the default gateway if the data are not in the same subnet.

After receiving the packet from the l3 module, users can check the operation status in the routing table. It will build up a new frame head, of which the source MAC address is the MAC address of the default gateway, and the destination MAC address is the MAC address of equipment B. It can establish corresponding relations between A and MAC address, forwarding port of B through a certain recognition mechanism. Also, it will record into a flow cache list, and all the data from A to B will be operated through the l2 switching module directly, namely is “A routing process, multi-times forwarding”.

The above is a simple summary of the work process of the l3 switch, which shows the characteristics of the l3 switches:

1. High-speed forwarding of data by combining hardware.

2. It is not a simple superposition of l2 switches and routers, the l3 routing module is directly added in the high-speed backplane bus of l2 switching and breaks through the rate limit of traditional router interface, and the rate can reach dozens of Gbit/s. The switching capacity, these are two important parameters of the performance of l3 switches.

3. Most of the data, except the necessary routing operated by the routing software, are forwarded at high speed by the l2 module. Routing software is mostly through efficient optimization, not a simple copy router.

Conclusion

Due to there isn’t much influence of broadcast in small-scale LAN, it is a widely used l2 switch. Fast switching function, multiple access ports, and cost-effective price ensure that l2 switches provide a perfect solution for small-scale network systems.

The most important function of the l3 switch is to speed up the rapid forwarding of data for large-scale networks. The routing function is also served for this purpose. If large networks into small local area networks according to departments, regions, and other factors, it will result in a large number of Internet visits, and the l2 switch can not handle these large of visitors.

If simply want to use the router, it will limit network speed and speed due to the limit of interface numbers and low speed of router forwarding. Therefore it is better to use a l3 switch with routing function and fast forwarding speed.