VMWare Virtual Network
                                          (CISS-150 – William Jojo)


Hereafter, the ...
Network View

The guests and the host all have their own view of networking within their world. We can map the
complete ne...
ways from identifying important servers, gateways to other networks and for help in multicasting.

With all of this information, we can now develop a complete network diagram as depicted in
Illustration 5.

Dynamic Versus...
Simply gather the data of each guest as
                                                               shown above, record...

In the directory /etc/vmware/vmnet8/nat there is a file nat.conf. The following line should be added as a
Wrap Up

The guest network changes thus far are still a little incomplete. The main purpose here was to illustrate
what is...
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VMWare Virtual Network


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VMWare Virtual Network

  1. 1. VMWare Virtual Network (CISS-150 – William Jojo) Terminology Hereafter, the term host will refer to the computer and operating system that is hosting the VMWare server software. The term guest will refer to any virtual machine running in the VMWare environment on the host. Introduction When we set up the guests we will have chosen Network Address Translation (NAT) for the network connection. The VMWare environment not only virtualizes the hardware such as hard drives, CDROM, CPU's and memory, but also the network. The host system running VMWare for a guest operating system (OS) has three additional adapters know to the host system: vmnet1 and vmnet8. The adapter vmnet0 is also available, but no necessarily visible. The vmnet0 adapter is used for the bridging mode. Bridging mode is used when the guest OS will have an IP address on the same network as the host system. This allows the guest OS to participate in all communications as if it were an independent physical server on the network. The vmnet1 adapter is for host-only mode where the guest OS will communicate with other guests and the host. There is no method to access beyond the host in this mode. The adapter vmnet8 is used for Network Address Translation (NAT). The NAT feature allows the guest OS to be on a private network, but have access to the Internet and other services by using the host network adapter. All external requests are done on behalf of the guest as if the host OS where making the request itself through a method of remapping ports and noting the originator. Results of the request are then passed back to the guest OS that originated the request. Illustration 1: Ubuntu host network settings. VMware Virtual Network (20100208) 1
  2. 2. Network View The guests and the host all have their own view of networking within their world. We can map the complete network by simply gathering the details for each guest and the host. We'll start with the host. The host in Illustration 1 shows the setting of a laptop running VMWare server. The eth0 adapter (not shown) is wired and eth1 is wireless. The loopback adapter (lo0) is present as are the host-only (vmnet1) and NAT (vmnet8) adapters. This specific example shows a wireless adapter on the laptop (eth1) connected to Verizon DSL via private network ( which is likely Illustration 2: Windows XP guest OS network settings. NAT connected to Verizon for internet access. The guest OS will still have access to the internet, there's just additional translation happening from the guest to the host out to DSL modem and finally to the internet. Notice that the two vmnet networks have 24 bits ( of subnet mask. This means that 24 of the 32 IP bits represent the subnet and 8 bits represent the hosts in that network yielding 256 addresses available in the network, but only 254 (1-254) are usable. In the fourth octet, the value 0 (all workstation bits off) represents the network and a value of 255 (all workstations bits on) represents the broadcast address for that network. The first three octets will be fixed in both networks yielding vmnet1 fixed at 172.16.1.x and vmnet8 fixed at 172.16.104.x. It is important to note that these ranges are not identical for every installation of VMWare Server. It is not unusual for one network to be 172.16.89.x and the other to be 192.168.49.x. During the installation of the server software, these networks are selected based on discovery and knowledge of the machines current networking arrangement. The two virtual adapters (vmnet1 and vmnet8) that connect the host to VMWare are using the value 1 for the fourth octet. This is conventional wisdom at work where the lowest IP addresses are often used in a variety of Illustration 3: Windows 2003 guest OS network settings. VMware Virtual Network (20100208) 2
  3. 3. ways from identifying important servers, gateways to other networks and for help in multicasting. The Windows XP guest OS network settings are shown in Illustration 2. We can see in this example that the guest OS is configured for Dynamic Host Configuration Protocol (DHCP) and the guest received a lease from – the same subnetwork as the guest and the same subnetwork of the host's vmnet8 (NAT) adapter. The subnet mask is the same as the host and the default gateway indicates that the guest will send packets to unknown networks at that address. We can now build a flow of data from the Illustration 4: Ubuntu 7.10 guest OS network settings. WinXP guest ( to the internet through its (vitrualized) ethernet adapter into the vmnet8 network by way of the NAT device ( which is received on the other side of the NAT by the host ( It is possible for certain protocols originating external to the host to be forwarded to a guest OS and, therefore, grant a user access to a virtual machine within VMWare. See Advanced NAT Configuration for an example of how to set up access to existing guest SSH or Web servers using the VMWare host system as the gateway. Illustration 3 and Illustration 4 show the network settings for guests Windows 2003 server and Ubuntu Linux. The Linux environment requires the routing table information containing the default gateway to be displayed with a separate command (netstat -nr) whereas this data is contained in the Windows ipconfig information. The default route is shown as or the word default. Illustration 5: VMWare network view. VMware Virtual Network (20100208) 3
  4. 4. With all of this information, we can now develop a complete network diagram as depicted in Illustration 5. Dynamic Versus Static IP Addressing There are many schools of thought on whether an IP should be static, meaning never changing unless acted upon by another human, or dynamic using a protocol like DHCP. Using the DHCP protocol, if there are situations where you may run out of IP addresses for a given subnetwork because of unexpected growth, you have the flexibility to modify the DHCP configuration such that you can change the subnet mask and effectively double the number of clients that can be on that subnetwork. Users simply reboot their computers and the previous leases will not be honored and new leases granted. Of course, you could also create another subnetwork altogether. The network and system administrators must determine what makes the most sense in this situation. Consider the amount of work necessary to change systems that are statically configured when this situation presents itself. Still there are situations where statically configured hosts makes sense. Long-lived servers such as Oracle RDBMS and Web servers should be configured statically. If these are expected to be accessed via the Internet one cannot wait for DNS servers around the world to age their cached entries and finally update them with the new data. This can take hours, days and sometimes weeks to complete. In practice, the use of static IP addressing should be Illustration 6: Static Assignment of IP address in Windows XP limited to long-lived servers and DHCP used elsewhere when possible and appropriate. The configuration and restrictions placed upon the use of DHCP may vary depending on the internal politics and needs of your IT department. Now, all that information aside, we will statically assign the IP addresses in the virtual machines once the VMWare environment has assigned them through DHCP. This is done for several reasons, not the least of which being certain IP's haven't changed over the course of time during the semester, but also because the simple installation of Active Directory on a guest machine configured with DHCP will force a hard coded IP for the virtualized Ethernet adapter. The IP chosen by Windows is often in a different IP range than what was configured in the vmnet1 or vmnet8 networks. VMware Virtual Network (20100208) 4
  5. 5. Simply gather the data of each guest as shown above, record the information in a safe place and then proceed to configure each guest. Configuration of Windows XP is show in Illustration 6. Select Control Panel from the Start Menu and switch to classic view. Double-click Network Connections, right click on Local Area Connection and double-click Internet Protocol. Configuration of Windows 2003 is show in Illustration 7. From the Start menu, select Control Panel/Network Connections/Local Area Connection. Click Properties and double-click Internet Protocol. Illustration 7: Static assignment of IP address in Windows 2003 Server Configuration of Ubuntu 7.10 is shown in Illustration 8. From the Gnome menu, select System/Administration/Network. You'll be prompted for the superuser password. Double- click the Wired Connection, select Static IP Address under Configuration. If the network for Ubuntu does not start correctly, you may need to stop and start the network from a terminal as root using: sudo /etc/init.d/networking  stop sudo /etc/init.d/networking  start Advanced NAT Configuration To allow access to a guest on the vmnet8 network via the host, one only need add a line to the configuration file controlling the NAT setup on the host. Since the guests on the NAT side of the network cannot be directly accessed, we need to create a mapping that says, “Any connection coming in to the host on this port should be routed to this other host on this other port.” Our example will show the use of port 9022 inbound to Illustration 8: Static assignment of IP address the host as a means of accessing port 22 of the Ubuntu in Ubuntu 7.10 guest. This will redirect a SSH connection into the VMware Virtual Network (20100208) 5
  6. 6. guest. In the directory /etc/vmware/vmnet8/nat there is a file nat.conf. The following line should be added as a superuser (sudo) to this file under the [incomingtcp] stanza to allow access via ssh to the Ubuntu guest: 9022 = yourVMwareGuestIP:22 STOP! Be sure to substitute your VMware guest IP for yourVMwareGuestIP, save the configuration and shutdown all virtual guests and run the following from the host: sudo /etc/init.d/vmware stop sudo /etc/init.d/vmware start Restart the Ubuntu guest try to connect to the guest from a remote system that is not the host nor another guest. Illustration 9: SSH from academ into the Ubuntu guest via NAT. We are attempting to prove that we can travel through the NAT from the exterior side of the host, so try using ACADEM or another Windows PC as a means to get there. The pathway to the guest is shown in Illustration 9. From the ACADEM host, use the command below, substituting the real username and the DNS name or IP of the system hosting your guests. For example if your username is test1 and the hostname is bt05401 you would use the following. ssh ­p 9022 test@bt05401 It is important to note that we are attempting to access the Ubuntu guest from outside the host. This means that the attempt to connect to the guest must originate from somewhere that isn't related to the VMware host in any way. By connecting from ACADEM or from another PC in the lab we satisfy the requirement of starting from the outside and working our way in. VMware Virtual Network (20100208) 6
  7. 7. Wrap Up The guest network changes thus far are still a little incomplete. The main purpose here was to illustrate what is happening behind the scenes in the virtual network and to statically set the IP addresses of the guests to proceed with the next projects. Hopefully we've learned a bit more along the way. Command Review For Windows use ipconfig /all to find network information quickly. For Ubuntu use ifconfig ­a and netstat ­nr for interface and routing information. References: VMWare Guest OS Installation Guide – Item: GSTOS-ENG-Q207-198 – Revision: 20070530 Virtual Machine Guide – VMWare Server 1.0 – Item: SVR-ENG-Q206-227 – Revision: 20060706 VMware Virtual Network (20100208) 7