4 Replies Latest reply: May 15, 2013 2:56 PM by jtooo RSS

Unable to connect to the MKS: Failed to connect to server

alan833 Lurker
Currently Being Moderated

I receive this error trying to open a console session on a VM on host1 using the Vsphere Client from my computer.

I can do this fine on all the other hosts (which are all ESXi5)


From my computer I also cannot ping host1.

From my virtual center server I can both ping and open a console session just fine.


I am suspecting a firewall issue.  What would next steps be?


  • 1. Re: Unable to connect to the MKS: Failed to connect to server
    mrksiddiqui Hot Shot
    Currently Being Moderated

    In order for Mouse Keyboard Screen (MKS) you need to have proper network resolution. Are you able to resolve the host from your computer? if not I would start by looking at the reason why.

  • 2. Re: Unable to connect to the MKS: Failed to connect to server
    grasshopper Master vExpert
    Currently Being Moderated

    In addition to proper DNS, MKS depends on port 902 end to end (i.e. telnet <hostipaddress> 902).  MKS errors are almost always DNS or firewall.  The only exception to the 902 requirement is when using vCloud Director which can proxy that connection across 443 for your users.

  • 3. Re: Unable to connect to the MKS: Failed to connect to server
    StewartCollins Lurker
    Currently Being Moderated

    Here is a more clear answer:  it is recommend to always use FQDN for all server names including your vSphere client connection to your vCenter server and the vCenter server connection to each ESX(i) host.  So proper DNS registration is required.  vCenterServer and each ESXi host must have a FQDN A record established in your internal DNS servers.  My vCenter is on a Windows server, so it was auto created.  I manually added each ESX host with a FQDN A record.


    I was having the same issue "Unable to connect to the MKS: Failed to connect to server" while connected to vCenter while using just the NETBIOS name.  Realized I was using just the NETBIOS name for my vCenter server connection with the vSphere client.  I already added the ESX server record in DNS and vCenter was connected to it using a FQDN.  But since I was using only NETBIOS and a bad DNS server on my desktop computer, it apparently was unable to connect to the server name (either vCenter or the host) in order to launch a VM console screen.  I tested using the vCenter server's IP only as suggested in other post, but that had the same failed results.  It doesn't have anything to do with the port 902.  Closed vSphere again and reconnected to vCenter using FQDN, opened a VM Console window, and worked perfectly.

  • 4. Re: Unable to connect to the MKS: Failed to connect to server
    jtooo Lurker
    Currently Being Moderated

    I started to have this issue as well recently.

    The cause of problem for me is a little bit different. and I m posting here for some other people's reference.


    I found out that at the end, it's our network problem because I m on VPN.

    Port 902/903 is blocked I believe.


    I've asked a coworker of mine (not in VPN) and he can successfully telnet to the ESX --> telnet <ESX IP> 902

    But I can't while I am on VPN, even if I disabled all firewall.

    So I contact the IT dept and they resolved this.


    Hope this helps some people.

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