VLAN与三层交换机Learning content:
1.VLAN the concept and advantages of
the type of 2.VLAN
3. static VLAN configuration
4.Trunk introduction and configured
to forward the principle and configuration 5. The three switches
A, VLAN concept and the advantages of
the traditional switched Ethernet, all users are in the same broadcast domain, when a large-scale network, the number of broadcast packets to increase dramatically, when accounting for the total number of broadcast packets when an amount of 30%, the network transmission efficiency will be significantly decreased. Especially when a network device fails, the network will continue to send broadcast, causing a broadcast storm, so that network traffic paralyzed. So, how to solve the problem should it? We can use separate broadcast domains to solve this problem, there are two ways to separate broadcast domain.
- Physical separation. Physically dividing the network into several small networks, broadcast isolation can then use the routing device to connect to different networks for communication.
2. logical partition. The network is logically divided into several small virtual network, i.e. VLAN. VLAN works in the data link layer of the OSI reference model, a VLAN is a switched network, wherein all users are in the same broadcast domain, each connected to communicate through VLAN routing device. Using physical separation has many drawbacks, it will make the LAN design lacks flexibility.
Specifically, as shown:
VLAN having characteristics of flexibility and scalability, the VLAN technology:
1. Broadcast Control
2. enhance network security
3. Simplified Network Management
Two, VLAN species
(1) static VLAN is port-based VLAN, VLAN is the most common implementation. Static VLAN that is explicitly specified port switch belongs to which VLAN, which requires the network administrator to manually configure 
the same VLAN devices can communicate, different VLAN can not communicate
(2) Dynamic VLAN
MAC address-based VLAN dynamic
VLAN range 
Third, setting up a static VLAN to:
1. Create a VLAN
2. Add the appropriate port of the switch to a VLAN
3. Verify the VLAN configuration
to create VLAN There are two ways
1.VLAN database configuration mode (privileged mode) 
2. Global mode 
3. Create exemplary VLAN 
4. VLAN deleted 
5. the port to the VLAN 
6. the plurality of ports simultaneously added VLAN 
7. the restore default configuration interface 
8. verify VLAN configuration
VLAN configuration see post-test case!
Four, Trunk presentation and configuration
What is Trunk? 
Switched network, there are two types of links:
① access link: usually belong with a VLAN.
Intermediate link ②: can carry a plurality of VLAN. (VLAN can run all information on the relay link)
so it is the role of Trunk same VLAN can communicate across the switch.
VLAN identification
Specifically, as shown:
Usually two types of identification:
1.ISL (the Cisco proprietary standard) 30 bytes 
2.IEEE 802.1q 4 bytes
TRUNK configuration, as shown:
Note that: Ethernet channels: at least two or more links form, it must be Trunk port
features: increased link bandwidth
increases link reliability
TRUNK configuration test case will be released late! You can follow the operation together!
Five, three switches forward the principle and configuration
three-tier exchange technical 
principles of three-tier exchange
The three-switch virtual interface 
virtual interface acts as a gateway host 
three switches to configure 
a test case released under the three-switch!
Summary overview: to produce 1.VLAN LAN design adds flexibility enables network administrators subdivided workgroup, no longer constrained by the physical location of the user is located.
2.Trunk role is to make the same VLAN can communicate across the switch.
3. The three switches for switching and routing data packets through the hardware, simply the exchange is equal to three plus Layer 3 forwarding exchange.
4. The three switches includes a routing function, it is possible to access each other VLAN, VLAN interface for each network segment is the gateway.