Use a layer-3 Switch for inter-VLAN routing Communication

In fact, the essence of a layer-3 switch is a layer-2 switch with the routing function. The routing mainly belongs to the network layer function in the OSI reference model, so the layer-3 Switch also has the routing kinetic energy. Now, we know that computers with different VLANs can communicate with each other as long as they can provide routes between VLANs. However, if a router is used for inter-VLAN routing, as the traffic between VLANs increases, the router may become the bottleneck of the entire network.

The switch uses a dedicated hardware chip called ASICApplication Specified Integrated Circuit to process data frames. In many models, it can achieve Wired Speed switching at Cable Speed. Vrouters are basically software-based. Even if a data packet is received at a cable speed, it cannot be forwarded without any speed limit. Therefore, it becomes a speed bottleneck. In terms of Inter-VLAN routing, traffic is concentrated on the aggregation link of routers and switches, which is particularly easy to become a speed bottleneck. In addition, in terms of hardware, as vrouters and vswitches need to be set separately, it may be a problem to connect to the configured places in some small space environments.

Layer 3 Switch)

To solve these problems, layer-3 switches emerged. A layer-3 switch is essentially a layer-2 switch with a routing function ". A route is a function of the layer-3 network layer in the OSI reference model. Therefore, a switch with the layer-3 routing function is called a "layer-3 Switch ".

Vswitch module and vro module are set in a local machine. The built-in routing module is the same as the Switching Module, and ASIC hardware is used to process routes. Therefore, compared with traditional routers, high-speed routing can be achieved. In addition, the routing and switching modules are aggregated. Because they are internal connections, a considerable bandwidth can be ensured.

Use a layer-3 Switch for inter-VLAN routing in-VLAN communication)

How is data transmitted within a layer-3 switch? Basically, it is the same as connecting a vro to a vswitch using a aggregation link. Assume that the four computers as shown in the following figure are interconnected with layer-3 switches. When using a router to connect to a vrovlan, you generally need to set sub-interfaces corresponding to each VLAN on the LAN Interface, while a layer-3 Switch generates a "VLAN Interface" internally )". A VLAN interface is an interface used to send and receive data from each VLAN. Note: VLAN interfaces are called SVI -- Switched Virtual interfaces on Cisco Catalyst series switches)

In order to compare the routing between VLANs with the vro, let's also consider the communication between computer A and computer B. First, the data frame with the target address B is sent to the switch. It is found that computer B is connected to Port 2 by searching the MAC address list of the same VLAN. Therefore, the data frame is forwarded to Port 2.

Use a layer-3 Switch for inter-VLAN routing and inter-VLAN communication)

Next, let's imagine how computer A communicates with computer C. For the target IP address, computer A can determine that the communication object does not belong to the same network, so it sends data Frame 1 to the default gateway ). After retrieving the MAC address list, the switch forwards the data frame to the routing module through an internal aggregation link. When passing through the internal aggregation link, the data Frame is attached with VLAN identification information Frame 2 of the red VLAN ).

When receiving a data frame, the routing module first identifies the red VLAN from the VLAN identification information attached to the data frame, and then determines that the red VLAN interface is responsible for receiving and routing. Because the destination network 192.168.2.0/24 is a directly connected Router Network and corresponds to a blue VLAN, the blue VLAN interface is then forwarded back to the Switching Module through the internal aggregation link. When the data Frame passes through the aggregation link, it is attached with the identification information Frame 3 of the blue VLAN ).

After receiving the frame, the switch retrieves the MAC address list of the blue VLAN and forwards it to Port 3. Because Port 3 is a common access link, VLAN identification information is removed from Frame 4 before forwarding ). Finally, computer C successfully receives the data frame forwarded by the switch. The overall process is very similar to the situation when using external routers-both need to go through the sender → switch module → route module → switch module → receiver.