i had a similar problem where in i was using SKB_PUSH to add extra
header,,,, i used this... structure called flowi.... which can be used to
define a sort of traffic class...based on some combination of fields


iph->daddr =htonl(xxxxxx);
{
struct rtable *rt;
struct flowi fl;
memset(&fl, 0x0, sizeof(struct flowi));
fl.fl4_dst  = htonl(xxxxxxx);
fl.proto = IPPROTO_TCP;
if (!ip_route_output_key(&init_net, &rt, &fl))
{
iph->saddr= htonl(ntohl(rt->rt_src));

skb_dst_set(skb2, &rt->u.dst);

}

}


On Mon, Apr 2, 2012 at 2:12 PM, Kesava Srinivas [off-list ref]wrote:

HI Friends,
Looking for a Confirmation on my analysis.

Once after Capturing the Socket Buffer in PRE_ROUTING Hook; Manipulated
the Socket Buffer by using the "skb_pull" Kernel Function. Using skb_pull;
stripped 28 bytes (IP+UDP) which are the Part of outer UDP/IP Header. Now;
My intention was to route the skb based on the Inner IP Header which is
sitting after stripping 28 bytes. At the END; returned NF_ACCEPT.

Even though; skb_pull worked Fine., Kernel's Stack is still looking in to
Outer Header only for Routing the Packet.I expected ;Kernel will look the
Inner Header (As data Pointer was incremented by 28 bytes via skb_pull) and
Take decision based on the Inner one. But; that didn't  happened. It looks
to me like; we need to always use NF_STOLEN & should write our own code to
route based on the INNER HEADER. Was my conclusion correct ??

-Thanks in Advance,
VKS



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