Tag Archives: pvlan

VCAP-DCA Study guide – 6.3 Troubleshooting Network Performance and Connectivity


  • Identify virtual switch entries in a Virtual Machine’s configuration file
  • Identify virtual switch entries in the ESX/ESXi Host configuration file
  • Identify CLI commands and tools used to troubleshoot vSphere networking configurations
  • Identify logs used to troubleshoot network issues

Skills and Abilities

  • Utilize net-dvs to troubleshoot vNetwork Distributed Switch configurations
  • Utilize vicfg-* commands to troubleshoot ESX/ESXi network configurations
  • Configure a network packet analyzer in a vSphere environment
  • Troubleshoot Private VLANs
  • Troubleshoot Service Console and vmkernel network configuration issues
  • Troubleshooting related issues
  • Use esxtop/resxtop to identify network performance problems
  • Use CDP and/or network hints to identify connectivity issues
  • Analyze troubleshooting data to determine if the root cause for a given network problem originates in the physical infrastructure or vSphere environment

Tools & learning resources

Identify virtual switch entries in a VMs configuration file

Contains both vSS and vDS entries;


In the example VM below it has three vNICs on two separate vDSs. When troubleshooting you may need to coordinate the values here with the net-dvs output on the host;

  • NetworkName will show “” when on a vDS.
  • The .VMX will show the dvPortID, dvPortGroupID and port.connectid used by the VM – all three values can be matched against the net-dvs output and used to check the port configuration details – load balancing, VLAN, packet statistics, security  etc

NOTE: Entries are not grouped together in the .VMX file so check the whole file to ensure you see all relevant entries.


Identify virtual switch entries in the ESX/i host configuration file

The host configuration file (same file for both ESX and ESXi);

  • /etc/vmware/esx.conf

Like the .VMX file it contains entries for both switch types although there are only minimal entries for the vDS. Most vDS configuration is held in a separate database and can be viewed using net-dvs (see section 6.3.7).

Command line tools for network troubleshooting

The usual suspects;

  • vicfg-nics
  • vicfg-vmknic
  • vicfg-vswitch (-b) for CDP
  • vicfg-vswif
  • vicfg-route
  • cat /etc/resolv.conf, /etc/hosts
  • net-dvs
  • ping and vmkping

Continue reading VCAP-DCA Study guide – 6.3 Troubleshooting Network Performance and Connectivity

VCAP-DCA Study Notes – 2.2 Configure and Maintain VLANs and PVLANs

This is one of the smaller objectives plus only the PVLAN concepts and practices are new – VLAN support remains relatively unchanged from VI3 (although the vDS and it’s associated VLAN support is new).


  • Identify types of VLANs and PVLANs

Skills and Abilities

  • Determine use cases for and configure VLAN Trunking
  • Determine use cases for and configure PVLANs
  • Use command line tools to troubleshoot and identify VLAN configurations

Tools & learning resources

Types of VLAN

VLANs are a network standard (802.1q) which are fully supported in vSphere. They can be used to minimise broadcast traffic and as a security measure to segregate traffic (although like any technology there are weaknesses). Typical uses for VLANs with vSphere are to isolate infrastructure (vMotion, iSCSI and NFS) traffic and VM traffic.

There are three main ways of using VLANs with vSphere (covered in this VMware whitepaper);

  • Virtual guest tagging (VGT) – requires VLAN driver support in the guest OS
  • Virtual Switch tagging (VST) – common option, requires VLAN trunking on external switches
  • External switch tagging (EST) – less flexible and requires more physical NICs

In the Cisco world you set a port to be an ‘access port’ or a ‘trunk port’ if it’s going to carry multiple VLANs. VLAN IDs are 16 bit values giving a range of 0-4095. 4095 is used within vSphere to mean ‘all VLANs’ and is how you configure a portgroup when using VGT.

Configuring VLANs and VLAN trunking

For standard vSwitches you configure VLAN tags on portgroups. This configuration is done at the ESX host using the VI client (Configuration -> Networking);

  • Use VLAN 0 when no VLAN tags are present (EST)
  • Use VLAN 4095 to pass all VLANs (VGT)

Use a specific VLAN ID depending on the isolation required (VST)

Continue reading VCAP-DCA Study Notes – 2.2 Configure and Maintain VLANs and PVLANs