RE: Extracting UDP header from skb while forwarding

[Vankam Maheswar]

Hi,
You can access UDP header like this:

udp_header = (struct udphdr *)(skb->data + (skb->nh.iph->ihl *4));

Regards,
Mahesh.

-----Original Message-----
From: linux-net-owner@xxxxxxxxxxxxxxx
[mailto:linux-net-owner@xxxxxxxxxxxxxxx] On Behalf Of Shrikrishna Khare
Sent: Wednesday, April 30, 2008 7:14 AM
To: linux-net@xxxxxxxxxxxxxxx
Subject: Extracting UDP header from skb while forwarding

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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