Question : Cisco 3000 vpn concentrator Transparent Tunneling issue

I have a Cisco 3000 VPN concentrator using the 4.6 client. Under Transport on the VPN client, if I use Transparent Tunneling , I connect and login fine using Kerberos to a 2003 DC, but cannot ping or see anything on the inside network. If I turn off Transparent Tunneling, it works fine. I have the base group and user group set to allow IPSEC over UDP. Have a PIX 515E in front of it, but have bypassed/removed the PIX and still the same result. Some users it works, others it does not. Hit or miss with some ISP's. Looked at a connection with the problem and no blocking of protocols/ports on the local router. No other filters on the VPN are active except for the default private and public on the interfaces. Strange thing is we have a concentrator in another location which is an older IOS on it and it works fine. Tried playing with default gateway and routes on the VPN , and still no luck. Basically IPSEC over UDP does not work , only IPSEC. Turned on IPSEC /NAT-T on the concentrator, and then refuses to authenticate.

Answer : Cisco 3000 vpn concentrator Transparent Tunneling issue

Every symptom you have described so far is exactly what I was experiencing, and the problem was a firewall somewhere (usualy ISP) was blocking UDP Encapsolation.  BTW this can also be blocked by some NAT devices.

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