Implementation of 802.1Q VLAN protocol and 802.1P Protocol

This paper mainly introduces the implementation of the 802.1Q VLAN protocol in the Ethernet switch, and some basic contents of the 802.1P protocol, details of the implementation of the two Protocols, and reference data of the 802.1Q and 802.1P protocols.

First, 802.1Q protocol

802.1Q protocol, that is, Virtual bridged local area networks protocol, the main provisions of the VLAN implementation, below we first tell about the basic concept of VLAN.

Virtual LANs is currently developing rapidly, the world's major network manufacturers in their switch devices have implemented VLAN protocol, as the name implies, VLAN is a virtual LAN, for example, for QuidwayS2403 switch, Its 24 10MB Ethernet ports can be divided into several groups, such as protocol groups, ATM groups, test groups, and so on, so that each user within the group is just like in the same local area network (where the users of the Protocol group may be on many switches rather than a switch), and users who are not in this group cannot access members of this group.

In fact, the definition of a VLAN member can be divided into 4 categories:

1, according to the Port Division VLAN

This method of dividing VLAN is based on the port of the Ethernet switch, such as S2403 1~4 port for VLAN a,5~17 for VLAN b,18~24 VLAN C, of course, these belong to the same VLAN port can be discontinuous, how to configure, by the administrator decision, If you have multiple switches, for example, you can specify that switch 1 's 1~6 port and switch 2 's 1~4 port is the same VLAN, that is, the same VLAN can span several Ethernet switches, according to the Port division is currently the most common method of defining VLANs, IEEE The 802.1Q protocol provides a way to divide VLANs according to the ports of the switch. The advantage of this partitioning approach is that it is very simple to define a VLAN member, as long as all the ports are defined. The disadvantage is that if a user of VLAN a leaves the original port and has a port on a new switch, it must be redefined.

2, according to the MAC address Division VLAN

This method of dividing the VLAN is based on the MAC address of each host, that is, the host of each MAC address is configured which group he belongs to. The biggest advantage of this method of dividing the VLAN is that the VLAN does not need to be reconfigured when the user's physical location is moved, that is, switching from one switch to another, so it is considered that this method of partitioning the MAC address is based on the user's VLAN, the disadvantage of which is that when initializing, All users must be configured, if there are hundreds of or even thousands of users, the configuration is very tired. And this partitioning method also leads to a reduction in the efficiency of switch execution, because there may be a number of members of the VLAN group on the ports of each switch, so that broadcast packets cannot be restricted. In addition, for users who use laptops, their network cards may often be replaced, so the VLAN must be constantly configured.

3, according to the Network layer Division VLAN

This method of dividing VLANs is based on the network layer address of each host or protocol type (if multiple protocol is supported), although this partitioning method may be based on network address, such as IP address, but it is not a route, do not confuse the network layer routing. Although it looks at the IP address of each packet, but because it is not a route, there is no routing protocol such as RIP,OSPF, but the bridge exchange based on the spanning tree algorithm,

The advantage of this approach is that the physical location of the user has changed, there is no need to reconfigure the VLAN that he belongs to, and the VLAN can be partitioned according to the protocol type, which is important for network administrators, and this method does not require additional frame tags to identify VLANs, which reduces traffic on the network.

The disadvantage of this approach is efficiency, because it is time-consuming to check the network-level address of each packet (as opposed to the previous two methods), the general switch chip can automatically check the network packet Ethernet frame head, but to allow the chip to check the IP frame head, requires a higher technology, but also more time-consuming. Of course, this is also related to the implementation of various vendors.

4, IP multicast as a VLAN

IP multicast is actually the definition of a VLAN, that is to say that a multicast group is a VLAN, this division of the way to expand the VLAN to the WAN, so this method has greater flexibility, but also easy to extend through the router, of course, this method is not suitable for LAN, mainly inefficient, For the multicast of LAN, there are two-layer multicast protocol GMRP.

As can be seen from the above, a variety of different VLAN definition methods have their own advantages and disadvantages, so many manufacturers of switches have implemented more than one method, so that network managers can choose according to their actual needs, in addition, many vendors in the implementation of VLAN, the VLAN configuration complexity, Also provides a degree of automatic configuration and convenient network management tools.

In the past, vendors have claimed that their switches implement VLANs, but the methods implemented by each vendor are not the same, so they cannot interconnect each other, so that once a user buys a switch from a vendor, they cannot buy another vendor. Now, the VLAN standard is the IEEE 802.1Q protocol, only support the same open standards to ensure network interconnection, and protect network equipment investment.