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I am trying to setup a PPTP VPN using RRAS on Server 2008 R2. I've got RRAS setup and working, and clients can connect to it using Windows XP or Windows 7 (my two target platforms.)

However, my clients are experiencing problems when they start sending multicast packets. Everyone is joined to the same multicast group / port, but no client can see the multicast packets from another client. However, all clients can see the multicast packets that the server sends out, and the server can see the multicast packets from all the clients.

Here's a little picture:


CLIENT <---> CLIENT [FAILS : packet is not seen by other client]

So, it seems like there is some kind of isolation between the clients. This is not the desired behavior with IPv4 multicasting, everyone should see everyone else's packets. Strangely, the clients can ping each other, see each other's shares, etc. I didn't do any fancy RRAS setup, I just did the standard setup (VPN only) accepting all the defaults, using 172.17.*.* as my VPN network block.

Also, the server is running in a VM (Virtualbox 4.1.0, bridged networking) -- I don't think the VM is causing the problem though, since the client <---> server piece works ok. The host OS is Windows 7 x64.

So - I was wondering if you guys had any thoughts on this. All help is appreciated.


Apparently I was not entirely clear --- the clients experience problems if they join up to the VPN and then start multicasting over the VPN network. If they don't join up to the VPN (some people are in the same network/office so they can do that) everything works fine. However, I need to fix it so multicasting over the VPN because the clients are connecting from a variety of different networks....

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1. How is this related to the VPN? 2. What is the target multicast ip address? –  joeqwerty Jul 22 '11 at 0:59
"172.17.*.*" a flat /16 net or are there additional subnets? –  user48838 Jul 22 '11 at 1:07
Its related to the VPN because the clients are multicasting through the VPN (ie. the program binds to the VPN, then starts multicasting.) The multicast IP is port 8621. ---- Its a flat structure, 172.17.*.*/16 is the only network/subnet. –  debracey Jul 22 '11 at 2:38
On the VPN client end, what does the client see it's subnet mask as being? –  Chris Thorpe Jul 22 '11 at 3:29
The subnet mask is -- but that's the same mask that my server 2003 VPN (which is working) is using. So I dont think that's the problem... Interestingly the subnet mask in the RRAS configuration says –  debracey Jul 22 '11 at 15:03
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