Lan implementation VLAN instances (1)

I. What is layer-3 Switch and VLAN?
To answer this question, let's first look at the working principle of Ethernet. The working principle of Ethernet is that data that is combined into a frame by byte formed by binary bits is actually some electric pulse) transmitted in the wire. First, the nodes that need to transmit data on the Ethernet segment listen to the wires. This process is called CSMA/CD (arrier Sense Multiple Access with Collision Detection with conflicting monitoring carrier listener for Multiple Access). If another node is transmitting data, the listening node will have to wait until the transfer task of the transfer node ends. If two workstations are ready to transmit data at the same time, the Ethernet segment will send a "Conflict" signal. At this time, all workstation on the node will detect the conflicting signal, because the voltage on the wire exceeds the standard voltage. At this time, any node in the Ethernet segment can transmit data only after the conflict ends. That is to say, in the CSMA/CD mode, only one node can transmit data over a wire in a time period. The networked device that forwards Ethernet data frames is a hub, which is a layer-1 device with low transmission efficiency.
Conflicts reduce the bandwidth of Ethernet, and this situation is inevitable. Therefore, when more and more nodes are on the wire, the number of conflicts will increase. The obvious solution is to restrict the nodes on the Ethernet wire and perform physical segmentation on the network. Network devices that perform physical segmentation use bridges and switches. The basic function of bridges and switches is to send information only to other physical network segments. Therefore, if all the information is sent only to the local physical network segment, the information on the bridge and switch will not pass. This effectively reduces network conflicts. Bridge and switch are based on the target MAC Medium Access Control) Address to make forwarding decisions, they are Layer 2 devices. We already know the disadvantages of Ethernet and the impact of conflicts in physical network segments. Now, let's take a look at another cause of network speed reduction: broadcast. Broadcast exists on all networks. If they are not properly controlled, they will flood the entire network and produce a lot of network communication. Broadcast not only consumes bandwidth, but also reduces the processing efficiency of user workstations. For various reasons, the network operating system NOS uses broadcast, TCP/IP uses broadcast to resolve MAC addresses from IP addresses, and broadcast to declare through RIP and IGRP protocols, broadcast is also inevitable. The bridge and switch will forward all the broadcast information, but the router will not. Therefore, to control broadcast, you must use a router. A vro makes forwarding decisions based on layer-3 headers, target IP addresses, target IPX addressing, or target Appletalk addressing. A router is a layer-3 device.
Here, we can easily understand the layer-3 switching technology. Generally speaking, it is a technology that combines routing and switching into one. After the router routes the first data stream, a ing table between the MAC address and IP address is generated. When the same data flow passes again, the ing table is used to directly switch from Layer 2 instead of re-routing to provide line rate performance, which eliminates the network delay caused by router selection and improves the efficiency of packet forwarding. A switch using this technology is often called a layer-3 switch.
So what is a VLAN? VLANVirtual Local Area Network) is the meaning of Virtual LAN. VLANs can be logically divided into independent working groups based on functions, applications, and other factors without considering users' physical locations, each user host is connected to a switch port supporting VLAN and belongs to a VLAN. Members of the same VLAN share the broadcast to form a broadcast domain, and the broadcast information of different VLANs is isolated from each other. In this way, the entire network is divided into multiple different broadcast domain VLANs ).
Generally, if a workstation in a VLAN sends a broadcast, All workstations in the VLAN receive the broadcast, but the switch does not send the broadcast to any port on other VLANs. A layer-3 switch is required to send broadcasts to other VLAN ports.
2. How to configure a layer-3 Switch to create a VLAN

The following sections describe VLAN Based on Cisco switches. Cisco VLAN implementation is usually port-centric. The port connected to the node determines the VLAN in which it resides. There are two ways to allocate a port to a VLAN: Static and Dynamic. The process of creating a static VLAN is to forcibly allocate the port to a VLAN. That is, we first create a VLAN on The vtp vlan Trunking Protocol) Server, and then assign each port to the corresponding VLAN. This is the most common method for creating VLANs.
Dynamic VLAN formation is simple. The port determines the VLAN to which it belongs. That is, we first set up a VMPSVLAN Membership Policy Server) VLAN management Policy Server, which contains a text file containing the MAC address table mapped to the VLAN. The switch uses this ing to determine the VLAN to which the port is allocated. This method has great advantages, but it is very difficult and tedious to create a database.
The following example shows how to implement VLAN in a typical Fast Ethernet LAN. A typical LAN means that a core switch with a layer-3 switching function is connected to several Branch switches, which do not necessarily have layer-3 switching capabilities ). Assume that the core switch name is COM, and the Branch switches are PAR1, PAR2, PAR3 ......, The light module of Port1 is connected to the core switch, and the VLAN names are COUNTER, MARKET, and MANAGING .......
1. Set VTP DOMAIN
It is called a management domain. All switches that exchange VTP update information must be configured with the same management domain. If all the switches are connected by a trunk, you only need to set a management domain on the core switch, and all the switches on the network are added to this domain, in this way, all the switches in the management domain can understand the VLAN list of each other.
COM # Switch vlan database to VLAN configuration mode
COM (vlan) # vtp domain COM set VTP management domain name COM
COM (vlan) # vtp server sets the switch to the server mode
PAR1 # Switch vlan database to VLAN configuration mode
PAR1 (vlan) # Set vtp domain COM
PAR1 (vlan) # vtp Client sets the switch to the Client Mode
PAR2 # Switch vlan database to VLAN configuration mode
PAR2 (vlan) # Set vtp domain COM
PAR2 (vlan) # vtp Client sets the switch to the Client Mode
PAR3 # Switch vlan database to VLAN configuration mode
PAR3 (vlan) # Set vtp domain COM
PAR3 (vlan) # vtp Client sets the switch to the Client Mode
Note: To set the vswitch to the Server mode, you can create, modify, and delete VLANs and other configuration parameters for the entire VTP domain on the vswitch, synchronize the latest VLAN information transmitted by other switches in The VTP domain. The Client Mode means that the vswitch cannot create, delete, or modify VLAN configurations, nor store VLAN configurations in NVRAM, however, the VLAN information transmitted by other switches in The VTP domain can be synchronized.

2. Configure Relay
To ensure that the management domain can cover all Branch switches, relay must be configured. The Cisco switch can support any media as a trunk line. To achieve relay, you can use its unique ISL tag. ISLInter-Switch Link is a protocol that transmits VLAN information and VLAN data streams between switches, between switches and routers, and between switches and servers, by configuring ISL encapsulation on the port directly connected to the vswitch, you can allocate and configure VLANs across the entire network.
The core switch is configured as follows:

COM (config) # interface gigabitEthernet 2/1
COM (config-if) # switchport
COM (config-if) # switchport trunk encapsulation isl
COM (config-if) # switchport mode trunk
COM (config) # interface gigabitEthernet 2/2
COM (config-if) # switchport
COM (config-if) # switchport trunk encapsulation isl
COM (config-if) # switchport mode trunk
COM (config) # interface gigabitEthernet 2/3
COM (config-if) # switchport
COM (config-if) # switchport trunk encapsulation isl
COM (config-if) # switchport mode trunk
The configuration on the branch switch side is as follows:
PAR1 (config) # interface gigabitEthernet 0/1
PAR1 (config-if) # switchport mode trunk
PAR2 (config) # interface gigabitEthernet 0/1
PAR2 (config-if) # switchport mode trunk
PAR3 (config) # interface gigabitEthernet 0/1
PAR3 (config-if) # switchport mode trunk
......
Now, the management domain is set.