Information Technology Reference
In-Depth Information
Spanning Tree Protocol
In physical sw itches, Spanning Tree Protocol (STP) off ers redundancy for paths and prevents loops
in the network topology by locking redundant paths in a standby state. Only when a path is no
longer available will STP activate the standby path.
It is possible to link vSwitches together using a VM with layer 2 bridging software and mul-
tiple virtual NICs, but this is not an accidental coni guration and would require some effort to
establish.
vSwitches and physical switches have some other differences:
A vSwitch authoritatively knows the MAC addresses of the VMs connected to it, so there is
no need to learn MAC addresses from the network.
◆
Trafi c received by a vSwitch on one uplink is never forwarded out another uplink. This is
yet another reason why vSwitches do not run STP.
◆
A vSwitch does not need to perform Internet Group Management Protocol (IGMP) snoop-
ing because it knows the multicast interests of the VMs attached to it.
◆
As you can see from this list of differences, you simply can't use virtual switches in the same
way you can use physical switches. You can't use a virtual switch as a transit path between two
physical switches, for example, because trafi c received on one uplink won't be forwarded out
another uplink.
With this basic understanding of how vSwitches work, let's now take a closer look at ports
and port groups.
Understanding Ports and Port Groups
As described previously in this chapter, a vSwitch allows several different types of commu-
nication, including communication to and from the VMkernel and between VMs. To help dis-
tinguish between these different types of communication, ESXi uses ports and port groups. A
vSwitch without any ports or port groups is like a physical switch that has no physical ports;
there is no way to connect anything to the switch, and it is, therefore, useless.
Port groups differentiate between the types of trafi c passing through a vSwitch, and they
also operate as a boundary for communication and/or security policy coni guration. Figure 5.3
and Figure 5.4 show the two different types of ports and port groups that you can coni gure on
a vSwitch:
VMkernel port
◆
VM port group
◆
