Cisco VPN

i am able to connect but can not get on any of the corporate sites (except one).

Typically, when you are able to establish a VPN connection, the VPN client successfully navigated through the router to the VPN server. The AirPorts are VPN "pass-thru" devices for most VPN implementations . However, if you are having issues connecting to specific corporate servers or out from the corporate perimeter to the Internet, then the problem may be either proxy (server) or DNS (Internet) related.

Not to pan it off, but I would first suggest contacting your Corporate IT department to see if they can offer assistance. Of course, that would assume that your company supports Macs.

If that doesn't work, I would check the DNS settings (IP Addresses) that your MacBook gets when it is connects successfully to your corporate VPN when not going through the AirPort Extreme. Then, match these to what it gets when it does. Most VPNs offer two basic modes of operation: 1) Full Tunnel, and 2) Split Tunnel. In the first mode, all communications go through the VPN tunnel to your corporation and back. In this mode, you would NOT be able to access network resources on your local home network simultaneously. In the second mode, you could.

Try changing the mtu to 1400