The three-layer technology has been able to make a scorpion in the ear in recent years, and there are three layers of technology everywhere, but for some people, this is a very new technology. Of course, some people say that the three-layer exchange is not the router and the second. Stacking of layer switches, there is nothing new, is it really what they say? Let's take a look at the working process of a Layer 3 switch through a simple network.
Networking is relatively simple
Equipment using IP A------------------------ Three-layer switch ------------------ ------Device B using IP
For example, if A wants to send data to B and knows the destination IP, then A uses the subnet mask to obtain the network address and determines whether the destination IP is on the same network segment as itself.
If it is on the same network segment but does not know the MAC address required to forward the data, A sends an ARP request, and B returns its MAC address. A uses this MAC to encapsulate the data packet and sends it to the switch. The switch uses the Layer 2 switching module to search. The MAC address table forwards the packet to the corresponding port.
If the destination IP address is not displayed on the same network segment, then A needs to communicate with B. If there is no corresponding MAC address entry in the flow cache entry, the first normal data packet is sent to a default gateway. This default gateway Generally set in the operating system, corresponding to the third layer routing module, so it can be seen that for data that is not the same subnet, first put the MAC address of the default gateway in the MAC table; then it is received by the three-layer module. The data packet, query routing table to determine the route to B, will construct a new frame header, where the MAC address of the default gateway is the source MAC address, and the MAC address of the host B is the destination MAC address. Through a certain identification trigger mechanism, the correspondence between the MAC address and the forwarding port of the host A and the B is established, and the inflow cache entry table is recorded, and the data of the subsequent A to B is directly submitted to the layer 2 switching module. This is usually referred to as a route that is forwarded multiple times.
The above is a brief summary of the working process of the three-layer switch. It can be seen that the characteristics of the three-layer exchange:
1. High-speed forwarding of data by hardware combination.
This is not a superposition of a simple Layer 2 switch and router. The Layer 3 routing module is directly superimposed on the high-speed backplane bus of the Layer 2 switch, breaking the interface rate limit of the traditional router, and the rate can reach tens of gbit/s. Counting backplane bandwidth, these are two important parameters of Layer 3 switch performance.
2. Simple routing software simplifies the routing process.
Most of the data forwarding, in addition to the necessary routing to the routing software processing, are two-layer modules for high-speed forwarding, routing software is mostly processed high-efficiency optimization software, not simply copy the software in the router.
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