Measure to accelerate inter-VLAN Communication

According to the study so far, we already know that inter-VLAN routing must go through an external router or a layer-3 Switch's built-in routing module. However, sometimes not all data needs to go through the router or routing module ).

For example, if you use FTP File Transfer Protocol to Transfer a large File with a capacity of more than MB, due to MTU restrictions, the IP protocol splits the data into small pieces and transmits the data and reassembles the data with the receiver. The "Sending target" of the split data is identical. The same sending destination means the same destination IP address and destination port number. Note: specifically, TCP/UDP ports are used here ). Naturally, the source IP address and source port number should also be the same. Such a series of data streams are called "Flow )".

As long as the original data of the stream is correctly routed, the subsequent data should also be routed.

Based on this, subsequent data no longer needs to be routed by routers. By omitting repeated routing operations, you can further increase the speed of Inter-VLAN routing.

AccelerationVLANInter-route Mechanism

Next, let's take a look at how to use a layer-3 Switch for high-speed VLAN routing.

First, the first data block of the entire stream is forwarded by the switch as usual → router route → again by the switch to the target connected port. In this case, the results of the first data route are recorded in the cache and saved. The following information must be recorded:

L target IP Address

L source IP address

L destination TCP/UDP port number

L source TCP/UDP port number

L receiving port number switch)

L forwarding Port Number Switch)

L forwarding target MAC address

And so on.

After the second data block of the same stream arrives at the switch, you can directly query the information previously saved in the cache to find the "forwarding port number" and then forward it to the target connected port.

In this way, you do not need to relay through the internal routing module again and again, but only by the internal cache information of the switch, you can determine the port to be forwarded.

In this case, the switch performs similar processing on the data frame during router relay, such as rewriting the MAC address, TTL in the IP address header, and Check Sum verification code information,

By caching routing results on a vswitch, you can achieve Wired Speed at the cable Speed. The data transmitted by the sender can be routed at full Speed and forwarded to the receiver.

It should be noted that similar methods to accelerate inter-VLAN routing are mostly implemented by the unique technology of each vendor, and the name of this function varies with the manufacturer. For example, on a Cisco Catalyst Series Switch, this feature is called "Multi-Layer Switching Multi Layer Switching )". In addition to the layer-3 Switch's internal routing module, some models in the external router also support similar high-speed VLAN routing mechanisms.