Information Technology Reference
In-Depth Information
Between VMs and physical machines on the network
◆
For VMkernel access to networks for vMotion, iSCSI, NFS, or Fault Tolerance logging (and
management on ESXi)
◆
Take a look at Figure 5.2, which shows the vSphere Web Client depicting a vSwitch on an
ESXi host.
Figure 5.2
Virtual switches
alone can't provide
connectivity; they
need ports or port
groups and uplinks.
In this i gure, the vSwitch isn't depicted alone; it also requires ports or port groups and
uplinks. Without uplinks, a virtual switch can't communicate with the upstream network; with-
out ports or port groups, a vSwitch can't provide connectivity for the VMkernel or the VMs. It is
for this reason that most of our discussion about virtual switches centers on ports, port groups,
and uplinks.
First, though, let's take a closer look at vSwitches and how they are similar to yet different
from physical switches in the network.
Comparing Virtual Switches and Physical Switches
Virtual switches in ESXi are constructed by and operate in the VMkernel. Virtual switches
(referred to in the general sense as vSwitches) are not managed switches and do not provide all
the advanced features that many new physical switches provide. You cannot, for example, telnet
into a vSwitch to modify settings. There is no command-line interface (CLI) for a vSwitch, apart
from the vSphere CLI commands such as esxcli. Even so, a vSwitch operates like a physical
switch in some ways. Like its physical counterpart, a vSwitch functions at layer 2, maintains
MAC address tables, forwards frames to other switch ports based on the MAC address, supports
VLAN coni gurations, can trunk VLANs using IEEE 802.1q VLAN tags, and can establish port
channels. Similar to physical switches, vSwitches are coni gured with a specii c number
of ports.
Despite these similarities, vSwitches do have some differences from physical switches. A
vSwitch does not support the use of dynamic negotiation protocols for establishing 802.1q
trunks or port channels, such as Dynamic Trunking Protocol (DTP) or Link Aggregation
Control Protocol (LACP). A vSwitch cannot be connected to another vSwitch, thereby eliminat-
ing a potential loop coni guration. Because there is no possibility of looping, the vSwitches do
not run Spanning Tree Protocol (STP). Looping can be a common network problem, so this is a
real benei t of vSwitches.
