This is a really old reply to a really old post but I finally found a solution to this mess. I too couldn't ping my virtual cisco pix running in GNS3 from my host (Windows 7 32 bit). In XP I could. What I finally realized was that even wireshark was reporting bad checksums. After some heavy digging I ran into this wiki on the wireshark sitehttp://wiki.wireshark.org/CaptureSetup/Offloading. Ladies and gentlemen TCP, UDP, and IP checksumming being offloaded to the nic card is killing us all. Cool feature but something that really F's up WinPCAP. If the OS is no longer doing the packet checksums it appears to all software using WinPCAP that the packet is bad and it just drops. As soon as I disabled this feature on my laptop so that the OS does the checksumming again everything works great again. SNORT also suffered from this issue which is why I'm heading to their support forum next.
On my machine to turn off Offloading
I did the following: In Windows, go to Control Panel->Network and Internet -> Network and Sharing Center, click Local Area Connection Link of the connection to change then choose 'Properties' button. Press the 'Configure...' button, choose the 'Advanced' tab to modify the "IP V4 Checksum Offload" and "TCP Checksum Offload (IPV4)" and "UDP Checksum Offload (IPV4)".
I changed the setting from RX and TX Enable to Disabled so that the OS will compute the checksum. Note: I had to reboot my machine after the setting changes.
Hope this works for you as it did for me!
On my machine to turn off Offloading
I did the following: In Windows, go to Control Panel->Network and Internet -> Network and Sharing Center, click Local Area Connection Link of the connection to change then choose 'Properties' button. Press the 'Configure...' button, choose the 'Advanced' tab to modify the "IP V4 Checksum Offload" and "TCP Checksum Offload (IPV4)" and "UDP Checksum Offload (IPV4)".
I changed the setting from RX and TX Enable to Disabled so that the OS will compute the checksum. Note: I had to reboot my machine after the setting changes.
Hope this works for you as it did for me!
