Kernel 2.6 IPSEC and Firewall

Hi,

I am using Kernel 2.6.1 with ipsec-tools. I have two LANs and I try to
dig a tunnel between them.

When I try to ping a computer on the other network the logs indicate
that the tunnel was established, but the iptables firewall thinks that
the ICMP packets is routed through ppp0 and blocks it.

When I allow packets with destination or source 192.168.xxx.yyy to go
through my ppp interface, the ping works.

It seems like a security risk. Is it reasonable to allow this?

Nadav