Virtual PC, Shared Networking and the problems with Ping

Anyone who has spent time troubleshooting networking problems will be more than familiar with the tool - Ping. However - there are two problems with using ping with shared networking under Virtual PC:

1. 192.168.131.254 does not respond to a ping.

   One of the first steps in network troubleshooting is to try and ping your gateway address.  Unfortunately, with Virtual PC and shared networking, the gateway address (192.168.131.254) does not respond to a ping.  This is completely benign behavior - as all other aspects of networking still work - however it has tripped up many people who were trying to diagnose network connectivity with shared networking.

2. You can only ping external computers if you are running Virtual PC with an administrative user account.

   Virtual PC's shared networking implementation is a simple NAT engine.  Virtual PC is responsible for sending and receiving network traffic for the virtual machine as a standard Windows user mode application.  For security reasons, only applications that are running as an administrative user are able to generate translated ICMP packets, such as the ones that are needed to support ping with shared networking.

   N.B. This means that if you are running on Vista and want to use ping inside a virtual machine with shared networking, you will need to manually launch Virtual PC 'as administrator'.

Thankfully neither of these issues are show stopping problems, but are just interesting oddities.

Cheers,
Ben

• Anonymous
  April 30, 2007
  Hi, I have been working for the last two months with Virtual PC R2 under Vista on my Dell Inspiron laptop. For the NAT thing, If I want to ping the host OS and any of the other VMs, I create always two virtual NICs, one to the Microsoft Loopback and another using NAT. But you have to disable the Loopback if you want to access the outside network. My problem right now is that whenever I hibernate the laptop (just closing the laptop or selecting hibernating) the microsoft loopback hangs and I have to reboot the host machine to make it to work it again. It is annoying, since I am using a Windows machine for developing against another machine, and I keep different connections opened and I want to keep the system in the same state as I left it and be able to keep on working where I left the system. I have tried to disable/enable the loopback adapters (from the host or the guest machine) and even try to pause the VM. Nothing works. If someone could help me out, I would be grateful Miguel

• Anonymous
  May 06, 2007
  Miguel - I have not seen this behavior, and do not know what could be causing the problem you are seeing.  I would recommend that you contact Microsoft Product Support for help. Cheers, Ben

• Anonymous
  May 07, 2007
  Hi I have a different problem. I need to set up a testbed which has following topology: A-----B--Corporate Network--C----D A talks to B only and D talks to C only. I have two physical machines (H1 and H2), with Vista running on them. I have installed Virtual PC on H1 and H2, and installed two virtual machines on each of them. A and B are running on H1 and similarly C and D are running on H2. All the virtual machines have vista installed on them, and machines B and C have 2 NIC cards each. Due to policy of corporate network i cannot share the internet connection on my host machines and hence i'm not able to setup them as a NAT server. I tried giving A and 1 of the NIC card of the B as private IP address and using the other NIC card to talk to corpnet. And, I also enabled machines B and C as routers and added routes in their routing table. But the machines A and B (similarly C and D) are not able to talk to each other. Can any one tell me what have I done wrong or how shall i go about setting up this topology using virtual pc? Thanks in advance. Manveer

• Anonymous
  May 09, 2007
  There are cases where the inability to ping can be a show stopper - at least without rewriting some code.  I have a remote server maintenance toolkit that, just to make sure the server is alive, pings selected servers from a web service and returns the results to the server tech.  Not that I foresee it going to a virtual server any time soon but since we are virtualizing heavily so it could happen.  This app obviously won't be a good candidate for virtualization unless I replace the ping with an RPC call or other means of checking for a heartbeat.

• Anonymous
  May 15, 2007
  Hello, I am having trouble setting up the networking in MS virtual Machine 2007 In many places I have seen refrence to "loopback' or NAT, or "switch" In my options I have NAT but no switch or loopback. I have installed ubuntu linux as a web host test bed for testing php scripts before I upload to my live server. I can not ssh into the virtual machine as the network is not configured properly. Can you help?

• Anonymous
  May 24, 2007
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  May 24, 2007
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  May 25, 2007
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• Anonymous
  October 29, 2011
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