Question about tunnels, IPsec and redirect

Hi, I am looking at this patch: http://lists.openwall.net/netdev/2007/08/24/29 and I cannot understand it. Can somebody please try to explain ? more specifically: Can somebody please give an example of some setup of IPsec tunnel where the ip_rt_send_redirect() method should not be called when the skb->sp is not NULL ? (in other words, why if the SKB is and IPsec SKB, we should not send a redirect in such a case while forwarding a packet; note I am talking about IPv4) Note that the check for skb->sp was changed in recent kernels to skb_sec_path(skb), but it is essentially the same. Regards, Kevin