[Click] [click]

[Pradeep Pradeep]

Hello,

  
Thanks for the clue.
I have one more question. This is the explanation given for
set_network_header function.
_________________________________

void set_network_header (const unsigned char *header,
Method on Packet
          unsigned len)

Sets the network header annotation to header, which must lie between
buffer_data()
     and buffer_data() + buffer_length(). The network header is len bytes
long, so
     network_header_length() will equal len and transport_header() will
equal header
     + len.
______________________________________

Does this statement mean that transport header annotation's place is taken
immediately after network header annotation.? If this is the case I have a
problem. My packet format is

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

{IP Header}
{QoS Header}
{UDP Header}

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

 How should I use the set_ip_header()/set_network_header() for my case.?

One way I could think is to give the 'len' parameter as
'sizeof(click_ip)+sizeof(qos_header) '. Do I have to change
iph->ip_hl in
this case.(I mean to ask does this 'len' parameter indicates the length
of
the IP header OR placement of transport header relative to iph)

The Other way is to  bring in only the IP and UDP headers first, after
calling the Packe::make and then call 'set_ip_header to set both IP and UDP
header annotations and then insert QoS header between the headers so that
annotations will not change.

 Can you suggest which is a better way among these two and if possible any
other better way?

Regards,
Krishna.

_______________________
Previous
From: Beyers Cronje <bcronje at gmail.com>
Subject: Re: [Click] [click]SetIPChecksum
To: pradeep_addada at yahoo.co.in
Cc: click at pdos.csail.mit.edu
Date: Friday, 8 August, 2008, 6:47 PM

 Hi Pradeep,

p->ip_header() returns a pointer to the ip header of a packet, which is
stored in the ip header annotation of Packet. The ip header annotation is
set by elements such as MarkIPHeader and CheckIPHeader.

Packet::make() does not set this annotatio by itself, so you either have to
set it yourself by calling 'packet->set_ip_header(iph, iph->ip_hl
<< 2)' or
let a downstream element such as MarkIPHeader set it for you.

Beyers

On Fri, Aug 8, 2008 at 11:05 PM, Pradeep Pradeep <pradeep_addada at yahoo.co.in
> wrote:

> Hello,
>
>   In the code for the element SetIPChecksum element  there is part which
> tests if a packet is IP packet or not.
>
> It uses
> ---------------------
> ip=p->ip_header();
> if(!ip)
>
>   When can a situation arise which satisfies   !ip?
> -------------------------
>
>  I am genarating  packets which have the following format
> {IP Header}
>  {QoS Data}
> {UDP Header}
>
>
> The code I used is
> _______________________________
>
> void push(Packet* p)
> {
>
>
> WritablePacket *packet = Packet::make(0, 0, data_len+header_room, 0);
>
>   if (packet == 0) {
>       click_chatter( "cannot make packet!");
>       packet = NULL;
>       return;
>     }
>
>     // fill IP header
>
>    click_ip *iph = (click_ip*) packet->data();
>     memcpy(iph, p->ip_header(), sizeof(click_ip));
>     iph->ip_tos |= 0x0c;  // 12 for QoS
>     iph->ip_tos |= 0x01;  // Set ECN capability
>
>     // fill QoS fields
>     QoSSignalFormat* format =
>       (QoSSignalFormat*)(packet->data()+sizeof(click_ip));
>
>
>     // fill UDP header
>     click_udp *udph =
>       (click_udp*)(packet->data()+sizeof(click_ip)+sizeof(struct
> QoSSignalFormat));
>     memcpy(udph, p->udp_header(), sizeof(click_udp));
>
>        p->kill(); // destroy data packet
>     output(0).push((Packet *)packet);
>   }
>   _______________________________
>
> As you can see I am making some changes to IP header. So I want to
recompue
> the checksum by passing the packets through SetIPChecksum element. When I
> forward the these packets SetIPChecksum (which is slightly modified that
it
> detects the condtion !ip ) the packets are being struck at this !ip
> condtion. Please help me with this.
>
> Regards,
> Pradeep.





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