This article provides steps to verify the configuration of the network and to correct any issues that may be causing the lack of network connectivity. Note: the steps in the article may need to be performed through remote console such as iLo, iDRAC, KVM, etc.

Note: If connection to the default gateway is successful, but connections to other subnets are unsuccessful, then there is an issue in routing/Layer 3. Contact your network team to determine why the Layer 3 connections are failing.

Symptoms:

• An ESXi host is experiencing intermittent connectivity issues.
• An ESXi host cannot connect to the network.

VMware vCenter Server 6.7.x
VMware vCenter Server 4.1.x
VMware VirtualCenter 2.5.x
VMware vSphere ESXi 5.0
VMware vCenter Server Appliance 6.0.x
VMware vSphere ESXi 5.1
VMware VirtualCenter 2.0.x
VMware vCenter Server 5.1.x
VMware ESXi 3.5.x Installable
VMware vCenter Server 6.0.x
VMware vCenter Server Appliance 6.5.x
VMware ESXi 4.0.x Embedded
VMware ESX 4.1.x
VMware vSphere ESXi 5.5
VMware vCenter Server Appliance 6.7.x
VMware ESXi 4.0.x Installable
VMware vSphere ESXi 6.0
VMware ESX Server 3.5.x
VMware ESXi 4.1.x Embedded
VMware vCenter Server 6.5.x
VMware ESXi 4.1.x Installable
VMware vSphere ESXi 6.5
VMware ESXi 3.5.x Embedded
VMware vCenter Server 5.5.x
VMware vSphere ESXi 6.7
VMware ESX 4.0.x
VMware vCenter Server 5.0.x
VMware ESX Server 3.0.x
VMware vCenter Server 4.0.x

Notes: 

• If you are experiencing a complete lack of network connectivity from a particular virtual machine, see Troubleshooting virtual machine network connection issues (1003893).
• For information on how to test network connectivity to and from the ESXi host vmkernels, see Testing VMkernel network connectivity with the vmkping command (1003728).

Validate that each troubleshooting step below is true for your environment. The steps provide instructions or a link to a document, for validating the step and taking corrective action as necessary. The steps are ordered in the most appropriate sequence to isolate the issue and identify the proper resolution. Please do not skip a step.

1. Verify that the network adapter and server hardware are supported. For more information, see Verifying ESX/ESXi host hardware (System, Storage, and I/O devices) are supported (1003916).
    
2. Verify that the network link is up. For more information, see Network adapter (vmnic) is down or fails with a failed criteria code (2014553).
    
3. Verify the physical network adapter has the latest driver/firmware. For more information, see Determining Network/Storage firmware and driver version in ESXi (1027206).
    
4. Verify that proper VLAN IDs exist on the portgroup. For more information, see VLAN configuration on virtual switches, physical switches, and virtual machines (1003806).
    
5. If you are using NIC teaming on the virtual switch, verify that the physical switch ports are configured consistently for each teamed network adapter and that the proper load balancing policy is configured on the virtual switch. VMware recommends you to use the default Route based on the originating virtual port ID load balancing policy. If link aggregation on the physical switch is configured, use the Route based on ip hash load balancing policy. For more information, see NIC teaming in ESX/ESXi (1004088) and Host requirements for link aggregation (etherchannel, port channel, or LACP) in ESXi (1001938).
    
6. Verify that the speed and duplex of the network links are consistent. VMware recommends having the physical adapters set to auto-negotiate. For more information, see Configuring the speed and duplex of an ESX/ESXi Server network adapter (1004089).
    
7. Verify that port security is not configured on the physical switch ports. For more information, see Loss of network connectivity when port security is configured on the physical switch (1002811).
    
8. Verify that portfast (or equivalent) is enabled on all of the ESXi host's physical switch ports. For more information, see STP may cause temporary loss of network connectivity when a failover or failback event occurs (1003804).
    
9. Verify that all the NICs participating as uplinks on the vSS and VDS are observing all the network information. For more information, see Observed IP range does not show network in ESX or ESXi (1006744). 
   
   Note: Until the time the issue of observed IP range is not resolved on external physical network, you can set the problematic NIC in unused mode and then verify the networking functionality again.

If the problem still exists after trying the steps in this article, try to packet capture on the vmkernel or on the physical NIC to determine if the traffic is sent to the physical environment. For more information, see Using the pktcap-uw tool in ESXi 5.5 and later (2051814).