Application viewpoint: three applications of Multilayer Switch Technology

Multi-layer switches are worth learning. Here we mainly introduce three applications of multi-layer switch technology. At present, multi-layer switch technology is the focus of network technology, our online channels have already provided many reports for readers. Because of its importance, we will organize the system again for beginners to refer.

Using VLAN technology to build a local area network provides great convenience for network management. administrators can organize network resources based on working groups or business types independently of geographical locations. However, VLAN management also brings additional workload. For example, to set a VLAN in a campus network, if you need to add a VLAN, the network administrator needs to set the VLAN on each vswitch separately. In this way, the workload is large and tedious, on the other hand, it is easy to cause Network Planning inconsistency. People who can log on to the switch console can add or delete a VLAN on any switch.

To maintain VLAN configuration consistency on all vswitches of the campus network, VTPVLANtrunkprotocol is developed. VTP is a layer-2 protocol that allows you to add, delete, and change VLAN names to ensure the consistency of VLAN configurations, this makes it easier and more effective to maintain VLAN configurations on a large-scale switched campus network.

Vtp id of the vswitch

VTP uses the "domain" domain) to organize the interconnected switches, and maintains the consistency of VLAN configuration information on all switches in the "domain. The "Domain" relationship is established and maintained through the domain name. A group of vswitches that use the same domain name form a "domain ". The multi-layer switch technology can only be configured to belong to one VTP domain. The default working mode of a vswitch is server mode. The "Domain" name is defined by a switch working in server mode. a switch in server mode can also create, modify, and delete VLANs. You can configure global parameters for the VTP domain. VTP has its own NVRAM, which means that the VTP information cannot be cleared when the configuration file is deleted. When the VLAN configuration information is modified, this change will be advertised to all vswitches In The VTP domain. In addition, it can synchronize VLAN configuration information with other Switches Based on the received VTP announcement.

A vswitch working in the client mode cannot create, modify, or delete VLANs. However, you can update your VLAN configurations based on the received VTP announcement, the client can also advertise its current VLAN configuration information to the domain. A vswitch working in transparent mode does not send VTP notifications or modify its VLAN configurations based on received VTP information, but can forward VTP notification information. Switches Working in transparent mode can independently create, modify, and delete their own VLANs.

VTP Operating Principle

The VTP announcement information is transmitted on the trunk link of the vswitch. The VTP announcement contains a parameter called the configuration revision version configurationrevision. The configuration revision version number indicates the New and Old VLAN configuration information. The high version number indicates the updated VLAN configuration. As long as the switch receives an update with a higher version, it uses the vlan information in The VTP update to overwrite the current vlan information, therefore, the configuration revision version number plays an important role in VTP update. Each time a server modifies a VLAN configuration, including creating or deleting a VLAN and changing the VLAN name, the version number is added with 1, and the new version number is used to notify the domain.

If the version number of the published configuration is higher than the current version number of the vswitch that receives the notification, the vswitch uses new information to update its current configuration. This update process means that when the server deletes all its VLANs and uses a higher configuration version, all devices in the domain with a lower configuration version will also delete their VLANs. Reminder: A vswitch with the server identity in other domains is added to another VTP domain as the client identity, if the version number of the configuration revision carried by this switch is higher than the version number of the configuration revision in the current domain to be added, the VLAN database of the new client will overwrite the server and client databases in the current domain. Therefore, we recommend that you set a password for the VTP domain without a password by default), so that only the multi-layer switch technology that matches the password can be added to the domain.

Cross-VLAN Communication Method

Two important attributes of a VLAN are: a VLAN forms a broadcast domain, and a VLAN equals a logical subnet. Only routers in a connected network can be divided into broadcast domains or isolated broadcasts. Routers are also devices that route and exchange data for communication between different networks. Therefore, from this perspective, the communication between VLANs also needs routers as intermediate devices.

Generally, when using IP addresses to plan a network, different networks are connected through routers to enable mutual access between them. The problem is how to let the host send the data to the Internet to the router, to solve this problem, set the default gateway on the host. The default gateway is actually a vro. The host sends data packets to a non-local network and routes the data to the destination.

Since a VLAN is also a network, if a host in a VLAN needs to communicate with a host in other VLANs, you should also find a router as their default gateway in the same way described above, the router forwards data for them. There are two solutions. One is that a vswitch is connected to an external vro which serves communication between VLANs. This method is called an external routing method. The other is to use a high-end switch with multi-layer switching function, which has the routing function. This method is called the internal routing method compared with the external router method.

From the perspective of Layer 3, the communication between VLANs requires routers. From the perspective of Layer 2, the communication between VLANs also requires the routers to change the labels in the data frame. For example, when a VLAN3 host communicates with a VLAN4 host, the data marked with 3 enters from the vro3 interface connected to VLAN3. After routing, the data must be sent from the interface connecting to VLAN4, in this case, if the data mark is still 3, the data frame of VLAN3 will not be forwarded to vlan4. therefore, the data between VLAN3 and vlan4. To enable the VLAN3 data to reach VLAN4, The vro must replace the mark before sending the data, and change 3 to 4. In this way, the switch considers the data of VLAN4 to be the correct destination.