Basic knowledge about port initialization of A vswitch

There are many things worth learning about vswitch ports. Here we mainly introduce the process of accelerating vswitch port initialization. It may take 30 seconds or more to connect a computer to a vswitch before the computer can communicate over the network. If you are waiting for a long time, 30 seconds of waiting will make you feel very long. Let's take a look at how to accelerate the port initialization process of the switch.

Understanding the process of vswitch port Initialization

When you connect a device to the port of a started vswitch, The vswitch Port usually goes through four steps. Let's take a closer look.

Spanning Tree Protocol (STP) initialization

STP is an IEEE 802.1d protocol that prevents loops in a LAN. It is necessary to test the vswitch port. When STP is enabled, a loop is formed within the LAN. If a hub, vswitch, or vro is connected, STP is very important. On the other hand, if a computer, printer, server, or laptop is connected, the STP initialization process is not needed. During the STP initialization phase, the port goes through five stages of STP: blocking, listening, learning, forwarding, and failure. The entire process takes 15 seconds. Therefore, if you are sure what you want to connect to, you can terminate this process.

Test the Ethernet Channel Configuration

The next step is to test the Ethernet channel, which is bound with the switch port to provide more Ethernet connections. If one channel fails, the Ethernet channel usually provides redundancy. This process uses the port aggregation protocol (PAgP), which takes about 15 seconds.

Trunk configuration test wired and wireless networks

Next, the switch starts to test whether the port is Trunk (the port used for intercommunication between switches ). TRUNKING exchanges data between multiple VLANs through a single switch port. The test on the Trunk port takes very little time. Of course, you can disable it and save 1 or 2 seconds.

Adaptive switch port speed and full duplex

Finally, the switch port entry speed and full-duplex automatic handshake. For example, a vswitch port can support full duplex speed of 1000 Mb (1 Gb), but the client only supports full duplex of Mb, the maximum rate that the switch and customer can automatically negotiate with each other.

You can hard-code the process during vswitch initialization to save time. However, this is not always a good choice, because it may not know how fast the client supports. This adaptive time is not long, so consider whether it is worthwhile to perform hard encoding on each vswitch port.

Now we have reviewed the different phases of vswitch port initialization. Let's see how much time can be saved. Perform the following steps to save a port initialization time of more than 30 seconds for a Cisco IOS-based switch: Set the switch port to Access mode. This can cancel the Trunk negotiation and prevent the port from entering the Ethernet channel negotiation. This can save the initialization process 15 seconds. Configure PortFast. This can prevent the port from entering STP negotiation and save 15 seconds. The following is an example:

 
 

  
  
Switch(config)# int fa0/21  
  
  
Switch(config-if)# switchport mode access  
  
  
Switch(config-if)# spanning-tree portfast  
  
  
%Warning: Only enable PortFast on ports connected to a single host.  
  
  
Connecting hubs, concentrators, switches, bridges, etc. to this  
  
  
interface when you've PortFast can cause temporary bridging loops.  
  
  
Use with CAUTION.  
  
  
%This has configured PortFast on FastEthernet0/21 but will only  
  
  
have an effect when the interface is in a non-trunking mode.  
  
  
Switch(config-if)# no shutdown  
  
  
Switch(config-if)#  
  
  
Switch(config)# int range fastEthernet 0/1 - 24  
  
  
Switch(config-if-range)# switchport mode access  
  
  
Switch(config-if-range)# spanning-tree portfast  
  
  
Switch(config-if)# speed 100  
  
  
Switch(config-if)# duplex full 
 
 

By disabling STP initialization and Trunk negotiation, Ethernet channel negotiation can save 30 seconds for the initialization process. In addition, you can use the Range Command of the interface to set all ports of the switch.