I just set up iPhone tethering from my Snow Leopard Macbook Pro to my iPhone 3GS with the Datapro 4GB plan from AT&T. When attempting to connect to my corporate VPN from the MacBook Pro with Cisco VPNClient 4.9.01 (0100) I get the following log information:

Cisco Systems VPN Client Version 4.9.01 (0100)
Copyright (C) 1998-2006 Cisco Systems, Inc. All Rights Reserved.
Client Type(s): Mac OS X
Running on: Darwin 10.6.0 Darwin Kernel Version 10.6.0: Wed Nov 10 18:13:17 PST 2010; root:xnu-1504.9.26~3/RELEASE_I386 i386
Config file directory: /etc/opt/cisco-vpnclient

1      13:02:50.791  02/22/2011  Sev=Info/4 CM/0x43100002
Begin connection process

2      13:02:50.791  02/22/2011  Sev=Warning/2  CVPND/0x83400011
Error -28 sending packet. Dst Addr: 0x0AD337FF, Src Addr: 0x0AD33702 (DRVIFACE:1158).

3      13:02:50.791  02/22/2011  Sev=Warning/2  CVPND/0x83400011
Error -28 sending packet. Dst Addr: 0x0A2581FF, Src Addr: 0x0A258102 (DRVIFACE:1158).

4      13:02:50.792  02/22/2011  Sev=Info/4 CM/0x43100004
Establish secure connection using Ethernet

5      13:02:50.792  02/22/2011  Sev=Info/4 CM/0x43100024
Attempt connection with server "209.235.253.115"

6      13:02:50.792  02/22/2011  Sev=Info/4 CVPND/0x43400019
Privilege Separation: binding to port: (500).

7      13:02:50.793  02/22/2011  Sev=Info/4 CVPND/0x43400019
Privilege Separation: binding to port: (4500).

8      13:02:50.793  02/22/2011  Sev=Info/6 IKE/0x4300003B
Attempting to establish a connection with 209.235.253.115.

9      13:02:51.293  02/22/2011  Sev=Warning/2  CVPND/0x83400018
Output size mismatch. Actual: 0, Expected: 237. (DRVIFACE:1319)

10     13:02:51.894  02/22/2011  Sev=Warning/2  CVPND/0x83400018
Output size mismatch. Actual: 0, Expected: 237. (DRVIFACE:1319)

11     13:02:52.495  02/22/2011  Sev=Warning/2  CVPND/0x83400018
Output size mismatch. Actual: 0, Expected: 237. (DRVIFACE:1319)

12     13:02:53.096  02/22/2011  Sev=Warning/2  CVPND/0x83400018
Output size mismatch. Actual: 0, Expected: 237. (DRVIFACE:1319)

13     13:02:53.698  02/22/2011  Sev=Warning/2  CVPND/0x83400018
Output size mismatch. Actual: 0, Expected: 237. (DRVIFACE:1319)

14     13:02:54.299  02/22/2011  Sev=Warning/2  CVPND/0x83400018
Output size mismatch. Actual: 0, Expected: 237. (DRVIFACE:1319)

15     13:02:54.299  02/22/2011  Sev=Info/4 IKE/0x43000075
Unable to acquire local IP address after 5 attempts (over 5 seconds), probably due to network socket failure.

16     13:02:54.299  02/22/2011  Sev=Warning/2  IKE/0xC300009A
Failed to set up connection data

17     13:02:54.299  02/22/2011  Sev=Info/4 CM/0x4310001C
Unable to contact server "209.235.253.115"

18     13:02:54.299  02/22/2011  Sev=Info/5 CM/0x43100025
Initializing CVPNDrv

19     13:02:54.300  02/22/2011  Sev=Info/4 CVPND/0x4340001F
Privilege Separation: restoring MTU on primary interface.

20     13:02:54.300  02/22/2011  Sev=Info/4 IKE/0x43000001
IKE received signal to terminate VPN connection

21     13:02:54.300  02/22/2011  Sev=Info/4 IPSEC/0x43700008
IPSec driver successfully started

22     13:02:54.300  02/22/2011  Sev=Info/4 IPSEC/0x43700014
Deleted all keys

23     13:02:54.300  02/22/2011  Sev=Info/4 IPSEC/0x4370000D
Key(s) deleted by Interface (192.168.0.171)

24     13:02:54.300  02/22/2011  Sev=Info/4 IPSEC/0x43700014
Deleted all keys

25     13:02:54.300  02/22/2011  Sev=Info/4 IPSEC/0x43700014
Deleted all keys

26     13:02:54.300  02/22/2011  Sev=Info/4 IPSEC/0x43700014
Deleted all keys

27     13:02:54.300  02/22/2011  Sev=Info/4 IPSEC/0x4370000A
IPSec driver successfully stopped

The key line is 15:

15     13:02:54.299  02/22/2011  Sev=Info/4 IKE/0x43000075
Unable to acquire local IP address after 5 attempts (over 5 seconds), probably due to network socket failure.

I can't find anything online about this. I found a single entry for the error message in Google, and it was a swedish (or some other nordic language site) that didn't have an answer to the question.

I've tried connecting through both USB and Bluetooth tethering to the iPhone, and they both return the exact same results.

I don't have direct control over the firewall, but if changes are necessary to make it work, I may be able to get the powers-that-be to make adjustments. A solution that doesn't require reconfiguring the firewall would be far better of course...

Does anyone know what I can do to make this behave?

Thanks,

Dan