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Virtualization with VMWare Infrastructure 3.0

Archive for the ‘Virtual Switch’ Category


Posted by Preetam on April 7, 2008

Maximum amount of memory you can assign to service console is 800MB, 1600 MB is should be the

swap file size. VCB is license per host and not per processor as are VC,ESX,DRS,HA It is important to

note that virtual center uses a heartbeat per 5 min to check if license is up and changes are made to licenses.

HA Services running on the hosts itself and are NOT part of virtual center(VC), they are just configured using VC .

However DRS is controlled and managed by Virtual Center. DRS is driven by default interval of 5 min or when host

is added/moved from the cluster. So ideally DRS queries cluster 12 times in a hour. Based on this it prioritize series

of recommendations to level load across the cluster.


After logging level,Virtual Machine is the major factor in deciding the Virtual center database. Beware changing your logging level wipes out all your previous logged data.

One of the physical NICs will be allocated exclusively to the ESX console. It is through this ESX Server Service Console NIC that all connections to the ESX node are made, as well as SCP, SSH, or any other tool to access the ESX Server’s file system.

vmxnet virtual NICs can be utilized only after you install the VMware tools onto your virtual machine. When you replace Vlance NIC type to vmxnet NIC, you would have to re-ip the Virtual Machine. 

What is trunk port ?

It is port configured to carry traffic from multiple VLAN’s. This means every packet flowing through this port is tagged and other end(typically switch) knows where this packet belongs to. So in order to enable VLAN’s in Port which connects to NIC on ESX should be trunked(802.1q VLAN Trunk). Never forget to assign Native VLAN. Anything on Native VLAN is not tagged and whichever packet is not tagged it is not seen by Guest on ESX. And also configure port to allow other VLAN on it, this makes sure that all VLAN’s can been seen by the port.

What happens when you do “Service network restart” ?

It restarts eth0, service console nic and lo which is loopback adapter.



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Advance concepts

Posted by Preetam on October 27, 2007


The process by which one VM is unscheduled and another scheduled to execute is known as a world switch. This process involves capturing one VM’s processor registers and writing these registers to memory, and reading the registers for the other VM from main memory and, finally, writing these registers to the processor.

Beacon monitoring allows ESX Server to test the links in a bond by sending a packet from one adapter to the other adapters within a virtual switch across the physical links.

AMD PCNet PCI Ethernet adapter (vlance):. This device is used as the default because of its near-universal compatibility – there are DOS drivers for this adapter, as well as Linux, Netware, and all versions of Windows. However the virtual adapter reports link speeds of 10Mbps with only a half-duplex interface,

Vmxnet adapter: If the vlance adapter is not delivering acceptable throughput or if the physical host is suffering from excessive CPU utilization, higher throughput may be possible by changing to the vmxnet adapter, which is a highly-tuned virtual network adapter for VMs.

To handle multiple source MAC addresses, the physical network interface of the ESX server is put into promiscuous mode. This causes its physical MAC address to be masked; all packets transmitted on the network segment are presented to the VMkernel virtual switch interface. Any packets destined for a VM are forwarded to the virtual network adapter through the virtual switch interface. Packets not destined for a VM are immediately discarded.

In virtualization port-based tagging at the physical switch does not provide VLAN isolation between VMs that share the same physical network connection. To address the scenario where broadcast-domain isolation is required between two VMs sharing the same physical network, virtual switches support the creation of port groups that can provide VLAN tagging isolation between VMs within the confines of a virtual switch. Each port group is identified by a network label, which is unique to the current host, and can optionally have a VLAN tagging ID.

When an application within the VM issues a file read or write request to the operating system, the operating system performs a file-to-block conversion and passes the request to the driver. However, the driver in an ESX Server environment does not “talk“ directly to the hardware; instead, the driver passes the block read/write request to the VMkernel where the physical device driver resides and then the read/write request is forwarded to the actual physical hardware device and forwarded to the storage controller.

Unlike Windows and Linux operating systems, ESX Server does not lock a LUN when it is mounted. VMFS is inherently a distributed file system, allowing more than one ESX Server to view the same LUN. This means that, while numerous ESX Server instances may view the contents of a VMFS LUN, only one ESX Server may open a file at any given moment. To an ESX Server and VMFS, when a VM is powered on, the VM disk file is locked.

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Networking – VMWARE

Posted by Preetam on March 21, 2007

If you are using VLAN, in the VLAN ID field, enter a number between 1 and 4094. If you use VLAN ID 4095, port group would see traffic on any VLAN. Blade servers have limited number of NIC, it will be likely be necessary to use VLANs to separate traffic for SVC Console,Vmotion,IP Storage and various group of VMs.

IP Storage refers to any form of storage that uses TCP/IP to access SCSI devices

VMKernel TCP/IP networking stack has been extended to include

iSCSI & NFS (Virtual Machine Datastore,ISO files)

and Vmotion

Service Console and VMKernel Services have completely separate TCP/IP Stacks.

When only one service console connection is present, changing service console configuration is not allowed. Using DHCP for SVC Console, DNS server should be able to map SVC Console’s hostname to dynamically generated IP address. Otherwise you can use IP Address which again might change if lease expires, DHCP is supported only when virtual interface is configured and attached to the network where DHCP server resides.

iSCSI also has service console components, so networks that are used to access targets should be reachable by both Service console and VMKernel TCP/IP Stacks. As result, after you create VMKernel port for iSCSI you must create a SVC Console connection on the same vSwitch as the Vmkernel port.

When you select “Use this port group for VMotion” you broadcasting other ESX server to send Vmotion traffic on this network connection.

Uplink adapters default speed is Autonegotiate.

Layer 2 Security policy are promiscuous mode (by default Reject), MAC address change and forged transmits.Layer is data link layer.

Traffic shaping policies are set to each virtual adapter attached to the port group and not the vSwitch as a whole

Load balancing and failover policy allow you to determine how network traffic is distributed between adapters and how to re-route in case of failure of NIC. Outgoing traffic is controlled by this policy and incoming traffic by physical switch.

Use port group with different sets of active adapters in their teaming policy to separate VM into groups. These can use separate adapters as long as all adapters are up.

esxcfg-vswif -l

Provides a list of the service console’s current network interfaces.

Check that vswif0 is present and that the current IP address and Netmask are


esxcfg-vswitch -l

Provides a list of current virtual switch configurations.

Check that the uplink adapter configured for the service console is connected to the

appropriate physical network.

exscfg-nics -l

Provides a list of current network adapters along with their names

Check that the uplink adapter configured for the service console is up and that the

speed and duplex are both correct.

esxcfg-nics -s <speed> <nic>

Changes the speed of a network adapter.

esxcfg-nics -d <duplex> <nic>

Changes the duplex of a network adapter.

esxcfg-vswif -i <new ip address> vswifX

Changes the service console’s IP address.

esxcfg-vswif -n <new netmask> vswifX

Changes the service console’s netmask.

esxcfg-vswitch -U <old vmnic> <service console vswitch>

Removes the NIC for the service console

esxcfg-vswitch -L <new vmnic> <service console vswitch>

Changes the uplink for the service console.

If you encounter long waits when using esxcfg-* commands, it is possible that DNS is misconfigured.

Connection from Virtual network adapters to port group is made by name, any change in the name would cause loss of connection when VMs are rebooted. It won’t affect already running VMs. Best practise is to avoid renaming networks after they are in use.

Networking - VMWARE

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