How to Implement VLAN Technology for layer-3 switches

As a new generation of network technology, VLAN provides a good solution to the problems of flexible configuration of network sites and network security, the following describes how to update a VLAN on a layer-3 switch.

The filter service is used to set boundaries to restrict Frame Forwarding between members of different VLANs and between different protocols using a single MAC address and a group of MAC addresses. Frame filtering depends on certain rules. Based on these rules, the switch determines whether to forward or discard the corresponding frames.

Early 802.1d standard 1993), defines the basic filtering service, the switch must broadcast all the group MAC address packets to all ports. The new 802.1d standard 1998) defines the extension filtering service, which can also filter packets of group MAC addresses, and filter out all multicast address packets for the vswitch's outer port.

If no static or dynamic filter conditions are set, the vswitch uses the default filter conditions. The extended filtering service uses GMRP (Group Multicast registry Protocol) to control dynamic Group forwarding and Group filtering of vswitches by generating or deleting a Group or Group member.

Vswitches and workstations use GMRP to declare whether they are willing to receive frames from a group of MAC addresses. GMRP transmits such group information between vswitches on the Internet, so that vswitches can update their filtering information to implement extended service functions.

A vswitch has the filtering service and extended filtering service without any configuration. Because the old vswitches, hubs, and routers do not support dynamic multicast address filtering, the corresponding ports connected to them need to be configured with extended filtering.

The switch filters Frames Based on the filter database. The switch can maintain the filter database through dynamic learning and manual configuration. The vswitch checks and filters the database and determines whether the packet of a MAC address or vlan id should be forwarded to a port based on the following conditions:

The second layer supports port-based VLANs and MAC address-based VLANs. A port-based VLAN can quickly divide conflicting domains on a single switch. a mac address-based VLAN can support mobile applications on a laptop.

The layer-3 VLAN of a layer-3 switch can be manually configured or automatically generated by the switch. After the vswitch analyzes the data packets, it automatically configures VLANs to automatically update VLAN members. The layer-3 switch can work in a network environment where IP addresses are allocated in DHCP (Dynamic Host Control Protocol.

The switch can automatically discover IP addresses and dynamically generate VLAN Based on IP subnet. When a new IP address is assigned through DHCP, the layer-3 switch can quickly locate the address. Layer-3 switches update their VLAN member groups through IGMP, GMRP, ARP, and packet detection technologies. Through the Web-based network management interface, you can set the scope of automatic learning: Automatic learning can be completely unrestricted, partially restricted, or completely forbidden.

VLAN improves network performance by limits on sending and filtering. The layer-3 Switch updates the VLAN member table through listening and makes forwarding or filtering decisions based on the packet header member information. The following describes how a vswitch processes VLANs.

Data frame inbound:

Vswitches are classified based on the vlan id (VID) of the inbound data frame. One type is unlabeled, and the other is same. The vswitch determines whether to forward or discard a data packet based on the VID. At the same time, the vswitch can assign a VID to a frame without or with a priority mark.

VLAN tag:

If a data frame is not labeled with a VID, the switch assigns a VID to it and inserts the VID into its frame header. This process is called VLAN labeling. In this process, the switch processes packet forwarding and fills in the VLAN or priority field of the data frame.

The administrator can set the priority level to select the VLAN type and select the VID value. The default setting of a vswitch is to paste the IP subnet information, then the network protocol, then the MAC address, and then the inbound port of the data frame.

Measures taken to prevent information transmission congestion in computer networks. Traffic control can be implemented at multiple layers of the network. For example, in a TCP/IP network environment, you can use the ICMP protocol to suppress the source on the Layer 3, that is, the network layer to implement traffic control.

This mechanism is established between two sites on the point-to-point link. If the receiving site is congested, it can send a frame called a "paused frame" back to the Origin Site of the other end, indicating that the origin site stops sending packets during a specific period of time.

Before sending more data, the sending site must wait for the request time. The receiving site can send a frame back to the origin site at zero wait time, indicating that the Origin Site starts sending data again. A more complex method can change the sending frequency continuously. For example, the window mechanism adopted on the layer 4 of the network is the traffic control method.

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