Symptoms:

• Cannot connect or reconnect the ESX\ESXi host to vCenter Server.
• Adding an ESX\ESXi host to vCenter Server fails with the error:
  
  Cannot contact the specified host hostname\IP. The host may not be available on the network, a network configuration problem may exist, or the management services on this host may not be responding.
  
  
• After upgrading vCenter Server, a host does not reconnect to vCenter Server.
• You see the error:
  
  
  • Unable to access the specified host. It either does not exist, the server software is not responding, or there is a network problem.
  • Unable to add host to vCenter.
    
    
• In the /var/log/vmware/vpx/vpxa.log file, you see entries similar to:
  
  'App' 7338928 error] [VpxaHalCnxHostagent] Failed to discover namespace: Success
  'App' 7338928 warning] [VpxaHalCnxHostagent] Could not resolve namespace for authenticating to host agent
  'App' 4283312 verbose] [SchedulePolling] Last stats polling used [0] ms
  'App' 3076461728 verbose] [VpxaHalCnxHostagent] Creating temporary connect spec: localhost:443
  'App' 3076461728 error] [VpxaHalCnxHostagent] Failed to discover namespace: Success
  'App' 3076461728 warning] [VpxaHalCnxHostagent] Could not resolve namespace for authenticating to host agent
  'App' 5815216 verbose] [SchedulePolling] Last stats polling used [0] ms
  'App' 4017072 verbose] [VpxaHalCnxHostagent] Creating temporary connect spec: localhost:443
  
  
• In the /var/log/vmware/hostd.log file, you see entries similar to:
  
  
  • F66C36D0 panic 'App'] error: Invalid argument : No IP addresses found for addr='localhost', port=12001 : (0) 'Unknown error'
    F66C36D0 panic 'App'] backtrace:
    [00] eip 0xf7d21965
    [01] eip 0xf7c0e5c0
    
    
  • <YYYY-MM-DD>T<time>Z [FF8B5D20 info 'Solo'] webServer/port: 8309
    *** In-memory logs end ***
    error: N7Vmacore24InvalidArgumentExceptionE(Invalid argument : No IP addresses found for addr='localhost', port=8309 : (0) 'Unknown error')
    backtrace:
    backtrace[00] rip 16cff6e3 Vmacore::System::Stacktrace::CaptureWork(unsigned int)
    backtrace[01] rip 16b24268 Vmacore::System::SystemFactoryImpl::CreateQuickBacktrace(Vmacore::Ref<Vmacore::System::Backtrace>&)
    backtrace[02] rip 16ac2c95 Vmacore::Throwable::Throwable(std::string const&)
    backtrace[03] rip 16cc2b61 Vmacore::System::TCPServerSocketPosix::BindAndListen(std::string const&, int)
    backtrace[04] rip 050c4558 hostd [0x50c4558]
    backtrace[05] rip 050c87f0 hostd [0x50c87f0]
    backtrace[06] rip 050cbde6 hostd [0x50cbde6]
    backtrace[07] rip 16ae141b Vmacore::Service::AppImpl::StartPlugins()
    backtrace[08] rip 16adfd3f Vmacore::Service::InitApp(Vmacore::Service::Config*)
    backtrace[09] rip 05d4fe33 hostd [0x5d4fe33]
    backtrace[10] rip 05d45a28 hostd [0x5d45a28]
    backtrace[11] rip 05d53e52 hostd [0x5d53e52]
    backtrace[12] rip 1c886efc /lib/libc.so.6(__libc_start_main+0xdc) [0x1c886efc]
    backtrace[13] rip 050c4141 hostd [0x50c4141]</time>

Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.

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

This issue occurs when these entries are missing from the ESXi or ESX host file:

• 127.0.0.1 localhost.localdomain localhost
• ::1localhost.localdomain localhost

• Ensure that the /etc/hosts file is using 127.0.0.1 pointing to localhost.localdomain localhost.
  
  For more information, see:
  
  
  • Editing files on an ESX host using vi or nano (1020302)
  • Identifying issues with and setting up name resolution on ESX Server (1003735)
    
    
• Ensure that the host field within the /etc/nsswitch.conf file is set to hosts:files. Reboot the host to reflect your changes.
  
  Note: If using DNS for authentication, ensure that the hosts field is set to hosts:dns files.
  
  For more information, see Editing files on an ESX host using vi or nano (1020302).

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Restarting the Management agents in ESXi
Identifying issues with and setting up name resolution on ESX/ESXi Server
Editing files on an ESX host using vi or nano
VMware ESXi/ESX ホストの VMware vCenter Server への追加に失敗する
将 VMware ESXi/ESX 主机添加到 VMware vCenter Server 失败