Vigor 2860 on each site.

I have three sites, all connected together with a LAN to LAN VPN in a triangle type link.

If I then dial in to one of the routers with a L2TP with IPSEC Policy, I can access the 192.168.0.1 LAN at that site, and also the 192.168.1.1 and 192.168.2.1 LANS on the other sites too.
I can only achieve this when I dial into one of the sites, and it won't work when I dial into the others. I have the same firmware on each (3.8.5_RC6a_BT), and have tried to check settings are the same on all routers, but must be missing something?

Thanks for any advice!

I have just realised, the only difference is that on the site where it does work (should it by design?), the LAN DHCP server is external to the router, and I have reserved a block of IPs on the server for the router to use for VPN.