Information Technology Reference
In-Depth Information
Default Gateway
The default gateway is the virtual network's connection to the outside and other networks,
be it virtual or otherwise. In typical networking, the default gateway is often a network
router that sets the path and routes all packets in and out of the network. This router for-
wards traffic to remote subnets on behalf of a host.
In order for your virtual network to connect to the Internet, the easiest and most straight-
forward way is to have the virtual NIC running in bridged mode so that it is connected to your
physical NIC, allowing it to connect to all networks that the host is connected to.
If you are connecting different virtual networks together, there are various methods that
you can use:
The virtual machines themselves can be tricked to blindly route packets to all available
virtual subnets by making the default gateway IP address the same as the address of
the virtual machine. This will trick the virtual machine into sending the packet to itself
since it has been configured as the default gateway. It then sends the packet to the default
route of 0.0.0.0/0, allowing all hosts (VMs) on the subnet to receive it. All the virtual
machines that receive the packet will inspect it and either forward or accept it, depending
on whether they are the recipient or not.
You can create a virtual machine that will act as the routing mechanism for the various
subnetworks.
You can use an external physical router.
Netmask
The implementation for subnetting is the same as in regular networking. You still apply the
netmask through four octets, which determine the number of subnets in the network and
the subnet to which a specific computer belongs.
Bridging
Bridging refers to the connection being made by the virtual NIC to the physical NIC in
order for that particular virtual machine to appear as a unique machine on the host's
network along with other physical machines. It is analogous to a physical Ethernet switch
that is used to connect multiple network interfaces, both virtual and physical, on a single
machine while at the same time they share the same subnet. It is the easiest way to give
a virtual machine access to other machines on the host's physical network and not just the
virtual network. A dedicated IP must be allocated to the virtual machine to be connected
in bridged mode to give it its unique identity.
The following are the requirements for connecting a virtual machine in bridged mode:
A dedicated IP address for each virtual machine to be connected in bridged mode is
essential for the virtual machine to have its own identity on the network; it cannot share
the IP address of the host. This doesn't necessarily mean that it must have a static IP
address; it means that there should be an empty IP slot within the subnet for the DHCP
server to assign one to the VM.
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