problems with netfilter hook function for DHCP

[Subhash Gopinath <subhashg@xxxxxxxxx>]

Hello all,

I am facing problems capturing DHCP packets sent from a client to a server....
Basically, the hook function (defined below) is not getting called for
each packet going out of the system.. Any ideas ?

Thanks in adv,
Subhash

-------------------------------------------------------------------------------

#define DHCP_SERVER_PORT 67

unsigned int out_hook_func(unsigned int hooknum,
                      struct sk_buff **skb,
                      const struct net_device *in,
                      const struct net_device *out,
                      int (*okfn)(struct sk_buff *))
{

       struct udphdr *udp_hdr;
       struct sk_buff *sb = *skb;
       unsigned char *dhcp_hdr, *ptr;
       unsigned int len, sub_id, xid;

       printk (KERN_INFO "Here\n");
       /* Check if the message is valid and is a UDP message */
       if(!sb || !sb->nh.iph || sb->nh.iph->protocol != IPPROTO_UDP)
               return NF_ACCEPT;

       /* Check if the UDP message contains DHCP in the payload */
       udp_hdr = (struct udphdr *)(sb->data + ((sb->nh.iph->ihl)<<2));
       if(udp_hdr->dest != htons(DHCP_SERVER_PORT))
               return NF_ACCEPT;

       printk(KERN_INFO "DHCP packet\n");
       return NF_ACCEPT;

}

int init_module()
{
       /* Register Hook for packets sent */
       out_nfho.hook     = out_hook_func;
       //out_nfho.hooknum  = NF_IP_LOCAL_OUT;
       out_nfho.hooknum  = NF_IP_POST_ROUTING;
       out_nfho.pf       = PF_INET;
       out_nfho.priority = NF_IP_PRI_FIRST;
       nf_register_hook(&out_nfho);
}

void cleanup_module()
{
       nf_unregister_hook(&out_nfho);
}

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