Gentlemen, ladies, Hello, everyone. Today I share for you is knowledge of VLAN and Layer Switch, I will analyze three main aspects:
(1) Principle VLAN knowledge;
(2) Trunk theoretical overview;
understanding of (3) three-tier exchange;
A, VLAN principle of knowledge
1. Overview: split broadcast domains
(1) Physical segmentation: divide the network into several small from the physical network, using different network connection route together to achieve communication.
(2) Logical Segmentation: The network is logically divided into several small virtual network, i.e. VLAN. A VLAN is a switched network.
2.VLAN advantage
(1) controls the broadcast;
(2) enhance network security;
(3) simplify network management;
3. Static VLAN
Static VLAN is also known as port-based VLAN, VLAN is the most common way to achieve (a feature on the switch).
Static VLAN is explicitly specified switch ports belong to which VLAN, which requires the administrator to manually configure. When a user is connected to the host port of the switch, it is assigned to a corresponding VLAN.
Seen from the figure, hosts A and C in a range of VLAN 5, within a communication range; Hosts B and D in the VLAN 10, within a communication range.
4. (1) static VLAN configuration
VLAN 0,4095 and 1006-1024 using the system.
1 is the default numbers exist, do not create when used;
1002-1005,1025-4094 for the user to create, use and delete.
(2) VLAN basic configuration steps
A. Create VLAN;
---- a.VLAN database configuration mode (old version mode), but this mode only supports VLAN normal range (1 ---- 1005);
. ---- b global configuration mode, VLAN support not only the normal range and range can be configured VLAN database configuration mode can not be configured extended range (we use this model in the experiment).
B. The add switch ports to the corresponding VLAN;
C. Verify VLAN.
Two, Trunk theory Overview
1.Trunk Overview: The main achievement of inter-switch allows the host to communicate the same VLAN.
Function: a single link, and to distinguish between different VLAN identification data.
2. Two types of switching network link
(1) access link: belong to each VLAN, hosts connected to the switch links.
(2) relay link: can carry a plurality of link between the switch and the VLAN switch, usually we put router is connected to the link is called a relay link.
3. Package labeling procedure:
A.VLAN 10 to transmit data frames left switch, left switch receiving port bound VLAN 10, which randomly receives data sent by frames; `
B. In order for the switch to recognize the right of this data frame is VLAN 10, thereby giving it a marked identification VLAN 10, and then transmitted to the right side of the switch through a relay link;
C. After the right switch receives this determination based on the identification is VLAN 10, and VLAN 10 queries to the host, and finally delete the logo on the right switch, VLAN 10 are forwarded to the host.
4.VLAN logo
Of a relay on the Ethernet, two package types:
(. 1) the ISL (the Cisco proprietary standard) 
the ISL total package of 30 bytes: 26 byte header, 4 bytes at the tail.
(2) IEEE 802.1q 
marked identified as 4 bytes, i.e. length TPID and TCI in FIG.
5.Trunk configuration steps:
(1) enters the interface mode
(2) Select package type
(3) Trunk interface configuration, if no additional data transfer Trunk a VLAN, the VLAN can be deleted from the Trunk; likewise, may be added to the Trunk a VLAN.
(4) using the "show" command to verify Interface Mode
Third, the three-tier exchange of understanding
Layer 3 switching technology
(1) a three-layer switching technology for inter-VLAN communication
(2) = tier exchange Layer 3 forwarding switching +
2. Traditional MLS2 - 2
(1) Layer 2 switching ASIC informed rewrite information from Layer 3 engine to create an entry in the MLS hardware
(2) is responsible for rewriting and forwarding subsequent packets in the data stream 
working process: VLAN 1 wants to communicate with VLAN 2 there will be a lot of data packet transmission. When the first data packet to the routing query Layer three switches to VLAN 2 after that this segment of forwarding, to be forwarded to first re-encapsulated packet, VLAN 2 at this time need to send an ARP query signal, to get its MAC address. After re-packaged, the address to the routing and VLAN 2 is stored into the cache table, then the packet is transmitted to VLAN 2. After packets in the cache table to check only three switches, followed by transfer to VLAN 2.
3. CEF-based MLS
CEF forwarding topology model is based on
(1) the forwarding information base (the FIB)
(2) abutting relationship table