In precision of my previous post : this is what i added to the network.c for see the problem :
(l2tpd: network.c / around line 327) printf("select\n"); select (max + 1, &readfds, NULL, NULL, NULL); printf("select ok\n"); Sure, it's really simple ... But permit to discover the problem : "select" is displayed but "select ok" not ... Moreover, when i send UDP packet on the public interface (not throught IPSEC) l2tpd receive these without problem. For finish, i think it's not a routing porblem since the IP Sec SA was established (but i'm not an IP Sec specialist :)). Again, hope this can help ...