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For the iPhone and iPad running iOS 4.1 or later (multitasking) you need to download the free Cisco AnyConnect client. This is available from the Apple App Store. Enter the server as vpn.slac.stanford.edu. The native client is not supported.
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I could not ping vpn.slac.stanford.edu
From the internet, you should be able to ping vpn.slac.stanford.edu. However, after you have connected to the VPN servers, you will no longer be able to ping the vpn servers.
In order to test VPN connectivity, you should ping an internal SLAC only server; an example would be www-lanmonYou can't ping the vpn servers directly if you have established a VPN connection. You should be able to ping www.slac.stanford.edu to test your connection.