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I am running OS X 10.6.8 on a Santa Rosa MacBook Pro (MBP) (2.4Ghz). I have an ethernet connection that I share with an iPad and iPhone via the built-in WiFi (AirPort). In other words, my MBP is used as an Access Point (AP). So far so good. However, in addition, at times I want to share the VPN that I use from the Mac, via the ethernet, to the internet, over the wifi as well.

Is it actually possible to share an VPN L2TP (tunnelling through ethernet) connection over Airport, using the OS's Control Panel GUI? Or must I resort to the command line and scripts? I can easily share a PPTP (tunnelling through ethernet) connection in the Sharing Control Panel, and use that airport connection with my ipad, and the ipad can get to the internet.

PTPP Network connected

PTPP Shared

However, when I set up the L2TP share, in the same manner, the ipad connects to the wifi (airport) well enough, but refuses to get to the internet. The MBP itself can reach the internet, no problem.

L2TP Network Connected

L2TP Shared

I have researched this for a couple of weeks now, and not got very far in figuring out the difference between L2TP and PTPP, w.r.t. why L2TP fails, whereas the PTPP succeeds. The article Setup PPTP/L2TP VPN server on Mac OSX client OS using VPN Activator seems to suggest that there is a bug in Apple's Bonjour code. Is that true..? However, it states that the Bonjour code can not work across as VPN (PTPP and L2TP alike), but as my PTPP connection works correctly, I wonder whether the Bonjour bug is a red herring.

Nor am I using "Back to My Mac" (BTMM) as these two sites apply to imply there would be a port conflict:

The latter link is, yet again, a bit of a red herring as I am not using an Airport base station, just the built -in wifi on the MBP.

Another link, bemoaning L2TP whilst praising PPTP, Leopard Server VPN L2TP Not receiving connections, PPTP works fine? seems to suggest that Airport 7.5 is to blame, whereas Airport 7.4.2 works fine, however my AirPort Utility** claims to be version 5.6.1. Yet another red herring? I am starting to clutch at straws here.

I had originally followed Rodrigo Sieiro's excellent tutorial Using (and sharing) a VPN connection on your Mac , but it fails for L2TP, as it is more about OpenVPN and Tunnelblick.

When I start sharing the L2TP, the log messages are as follows:

04/01/2015 13:05:07 racoon[527] IKE Packet: transmit success. (Information message).
04/01/2015 13:05:07 racoon[527] IKEv1 Information-Notice: transmit success. (R-U-THERE? ACK).
04/01/2015 13:05:07 racoon[527] IKE Packet: receive success. (Information message).
04/01/2015 13:05:09 InternetSharing[559]    InternetSharing starting
04/01/2015 13:05:09 pppd[524]   l2tp_wait_input: Address added. previous interface setting (name: en0, address: 10.42.0.60), current interface setting (name: en1, family: Ether, address: 10.0.2.1, subnet: 255.0.0.0, destination: 10.0.2.255).
04/01/2015 13:05:09 named[564]  starting BIND 9.6-ESV-R4-P3 -c /etc/com.apple.named.conf.proxy -f
04/01/2015 13:05:09 named[564]  built with '--prefix=/usr' '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--disable-dependency-tracking' '--sysconfdir=/private/etc' '--localstatedir=/private/var' '--enable-atomic=no' '--with-libxml2=/usr/include/libxml2' 'CFLAGS=-arch x86_64 -arch i386 -arch ppc -g -Os -pipe ' 'LDFLAGS=-arch x86_64 -arch i386 -arch ppc ' 'CXXFLAGS=-arch x86_64 -arch i386 -arch ppc -g -Os -pipe '
04/01/2015 13:05:09 named[564]  running
04/01/2015 13:05:10 bootpd[563] server name MacBook-Pro.local
04/01/2015 13:05:10 bootpd[563] interface en0: ip 10.42.0.60 mask 255.255.255.0
04/01/2015 13:05:10 bootpd[563] interface en1: ip 169.254.7.184 mask 255.255.0.0
04/01/2015 13:05:10 bootpd[563] interface en1: ip 10.0.2.1 mask 255.255.255.0
04/01/2015 13:05:10 bootpd[563] interface ppp0: ip 46.246.115.250 mask 255.0.0.0
04/01/2015 13:05:10 bootpd[563] DHCP REQUEST [en1]: 1,8c:fa:ba:5a:bf:d0 <users-iPad>
04/01/2015 13:05:10 bootpd[563] DHCP REQUEST [en1]: 1,c8:6f:1d:d1:9d:ef <Roses-iPhone>
04/01/2015 13:05:11 bootpd[563] DHCP REQUEST [en1]: 1,c8:6f:1d:d1:9d:ef <Roses-iPhone>
04/01/2015 13:05:12 bootpd[563] DHCP REQUEST [en1]: 1,8c:fa:ba:5a:bf:d0 <users-iPad>
04/01/2015 13:05:14 bootpd[563] DHCP REQUEST [en1]: 1,8c:fa:ba:5a:bf:d0 <users-iPad>
04/01/2015 13:05:14 bootpd[563] ACK sent users-iPad 10.0.2.3 pktsize 300
04/01/2015 13:05:14 bootpd[563] DHCP REQUEST [en1]: 1,c8:6f:1d:d1:9d:ef <Roses-iPhone>
04/01/2015 13:05:14 bootpd[563] ACK sent Roses-iPhone 10.0.2.4 pktsize 300
04/01/2015 13:05:16 racoon[527] IKE Packet: transmit success. (Information message).
04/01/2015 13:05:16 racoon[527] IKEv1 Information-Notice: transmit success. (R-U-THERE? ACK).
04/01/2015 13:05:16 racoon[527] IKE Packet: receive success. (Information message).
04/01/2015 13:05:26 racoon[527] IKE Packet: transmit success. (Information message).
04/01/2015 13:05:26 racoon[527] IKEv1 Information-Notice: transmit success. (R-U-THERE? ACK).
04/01/2015 13:05:26 racoon[527] IKE Packet: receive success. (Information message).
04/01/2015 13:05:36 racoon[527] IKE Packet: transmit success. (Information message).

Thereafter, the associated log messages when attempting to use L2TP are a repetition of the following three messages:

03/01/2015 14:53:23 racoon[3818]    IKE Packet: receive success. (Information message).
03/01/2015 14:53:33 racoon[3818]    IKE Packet: transmit success. (Information message).
03/01/2015 14:53:33 racoon[3818]    IKEv1 Information-Notice: transmit success. (R-U-THERE? ACK).

Now, the AirPort Extreme and VPN Server question mentions that IKE packets use port 500/UDP, the same port that BTMM uses. However, as I have already stated, I am not using BTMM.

Finally, if I turn the MBP firewall off, then the ipad still can not reach the internet.

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