Extracting UDP header from skb while forwarding

[Shrikrishna Khare]

Hello All,

   My queuing discipline requires me to access destination port for UDP packets that I am sending. When I have machine A sending to machine B, a simple code like
struct udphdr* udp_header = udp_hdr(skb) works fine. 

 However, when I have A sending data to C through B (i.e. B as forwarding engine), I find that both, 
skb->transport_header and skb_network_header are equal when accessed from queuing discipline code. How can I access transport_header then? 

I tried extracting it from skb->data but the code keeps crashing. Could anyone please tell me how can I access transport header from queuing disciplines code then? I know machine B should not be looking at transport layer fields. But I need to do it for testing some functionality.

Thanks in advance!
Shrikrishna



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