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This chapter is from the book

This chapter is from the book

Redundant Physical Connection for Virtual Servers


How can a virtual server be kept connected when its physical connection fails?


If the virtual switch uplink port used by a virtual server fails, the virtual server becomes isolated and unable to connect to the network or any of its hosted IT resources.


A redundant, physical backup network connection is established for virtual servers.


A second physical network card is added to the physical host and is confi gured as a hot standby uplink port for the virtual switch.


Failover System, Hypervisor, Logical Network Perimeter, Physical Uplink, Resource Replication, Virtual Infrastructure Manager (VIM), Virtual Server, Virtual Switch


A virtual server is connected to an external network via a virtual switch uplink port. If the uplink fails (due to, for example, cable disconnection or port failure), the virtual server becomes isolated and disconnects from the external network.

The following steps are shown in Figure 4.23:

  1. A physical network adapter installed on the physical server host is connected to the physical switch on the network.
  2. A virtual switch is created for use by two virtual servers. Because it requires access to the physical external network, the physical network adapter is attached to the virtual switch to be used as an uplink to the network.
  3. The virtual servers communicate with the external network via the attached physical uplink network card.
  4. A connection failure occurs, either because of a physical link connectivity issue between the physical adapter and the physical switch (4.1), or because of a physical network card failure (4.2).
  5. The virtual servers lose access to the physical external network and are no longer accessible by their cloud consumers.

    Figure 4.23

    Figure 4.23 The steps that can lead to the separation of virtual servers from their external network connection.


One or more redundant uplink connections are established and positioned in standby mode. A redundant uplink connection is available to take over as the active uplink connection whenever the primary uplink connection becomes unavailable or experiences failure conditions (Figure 4.24).

Figure 4.24

Figure 4.24 Redundant uplinks are installed on a physical server hosting several virtual servers. When one fails, another takes over to maintain the virtual servers’ active network connections.


While the main uplink is working, virtual servers connect to the outside via that port. As soon as it fails, the standby uplink will automatically become the active uplink, and the server will send the packets to the outside via the new uplink. This process is also transparent to virtual servers and users.

While the second NIC is connected and receives the virtual server’s packets, it is not forwarding any traffic while the primary uplink is alive. If, and when, the primary uplink fails, the secondary uplink starts to forward the packets without any pause or interruption. If the failed uplink happens to come back into operation, it will take over the lead role and the second NIC goes into standby mode again.

The following steps are shown in Figures 4.25 and 4.26:

  1. A new network adapter is added to support a redundant uplink.
  2. Both network cards are connected to the physical external switch.
  3. Both physical network adapters are configured to be used as uplink adapters for the virtual switch.
  4. One physical network adapter is designated as the primary adapter, whereas the other is designated as the secondary adapter providing the standby uplink. The secondary adapter does not forward any packets.
  5. The primary uplink forwards packets to the external network until it becomes unavailable.
  6. When required, the secondary standby uplink automatically becomes the primary uplink and uses the virtual switch to forward the virtual servers’ packets to the external network.
  7. The virtual servers stay connected to the external physical network, without interruptions.

    Figure 4.25

    Figure 4.25 An example scenario of the utilization of a redundant uplink (Part I).

    Figure 4.26

    Figure 4.26 An example scenario of the utilization of a redundant uplink (Part II).


  • Failover System – The failover system is utilized to perform the failover of an unavailable uplink to a standby uplink.
  • Hypervisor – The hypervisor hosts the virtual servers and some of the virtual switches, and provides virtual networks and virtual switches with access to the virtual servers. If a virtual switch’s physical uplink becomes unavailable, this mechanism is responsible for forwarding the virtual servers’ traffic using another available physical uplink on the virtual switch.
  • Logical Network Perimeter – Logical network perimeters ensure that the virtual switches that are allocated or defined for each cloud consumer remain isolated.
  • Physical Uplink – This mechanism is used to establish connectivity between virtual switches and physical switches. Additional physical uplinks can be attached to a virtual switch to improve redundancy.
  • Resource Replication – Resource replication is used to replicate the current status of the active uplink to a standby uplink, so that the connection remains active without disruption.
  • Virtual Infrastructure Manager (VIM) – This mechanism is used to configure virtual switches and their uplinks, and performs the configurations on the hypervisors so that they can use another available uplink should an active uplink fail.
  • Virtual Server – This pattern is primarily applied in support of maintaining the network connections for virtual servers.
  • Virtual Switch – This mechanism uses the attached physical uplinks to establish physical connection redundancy that allows virtual servers to be redundantly connected to cloud consumers and the physical network.
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