[Click] No network header/Segmentation fault

[Beyers Cronje]

Hi,

I think you forgot to use Strip or specified the offset to MarkIPHeader in
your configuration. Also remember to use Classifier to only push proper IP
packets to MarkIPHeader, i.e. to get rid of ARP packets etc.
Your config should start with something like this:

FromDevice(eth0) -> Classifier(12/0800) -> Strip(14) -> MarkIPHeader ->
.......

Beyers

On Mon, Jul 7, 2008 at 10:33 AM, Tushar Soni <omega_marines at yahoo.com>
wrote:

>  Hi,
>
> Thanks for your reply. I tried both MarkIPHeader and CheckIPHeader, but
> when I use them it gives me segmentation fault. I think the
> reinterpret_cast<const click_ip *>(p->data()) is not working for this
> particular decoded packet.
>
> But I did try something. In my code after I decode I added the following
> lines:
>
> p->push(sizeof(struct click_ether));
> p->set_mac_header(p->data(), 14); //This sets the mac header as well as the
> network header
> click_ip *iph = p->ip_header(); //Now this works and returns the ip header
> p->set_network_header(20); //This essentially sets the transport header
> click_udp *udph = p->udp_header(); //This also works now
>
> After doing this when I push the packet, then the IPPrint() element (after
> stripping 14 bytes that i added) is able to print and there are no
> segmentation faults. So far so good. I send this packet to the tun. But
> somehow the packet is being dropped or not processed and it never reaches
> the application layer. I am thinking the initial reason why this packet does
> not have any network or transport header maybe causing the kernel to drop
> it. I checked the checksums of both ip and udp header and they seem to be
> correct. Would you have any ideas why this is happening???
>
> Thanks a lot for your help.
>
> Best Regards,
>
> Tushar
>
> Tºüçhé §übt!é
>
>
> ----- Original Message ----
> From: Beyers Cronje <bcronje at gmail.com>
> To: Tushar Soni <omega_marines at yahoo.com>
> Cc: click at pdos.csail.mit.edu
> Sent: Friday, July 4, 2008 5:27:59 PM
> Subject: Re: [Click] No network header/Segmentation fault
>
> Hi,
>
> You have to use either MarkIPHeader of CheckIPHeader elements to set the IP
> header annotations.
>
> Beyers
>
> On Fri, Jul 4, 2008 at 5:06 PM, Tushar Soni <omega_marines at yahoo.com>
> wrote:
>
>> Hi everyone,
>>
>> I have a scenario where coding some packets at the access point and
>> decoding the packets at receiver side using click. Now when i decode the
>> packet and use Print() element, the packet structure and ip header looks ok.
>> But when i use IPPrint it gives me segmentation fault. When i try to get the
>> ip header(Packet::ip_header()) or the udp header(Packet::udp_header()) it
>> returns null (so this is the reason why IPPrint does not work). The
>> commented code should explain better about what i am doing and the problems
>> i am facing. I would be glad if someone could help me figure out what i am
>> doing wrong. Thanks.
>>
>> Tushar
>>
>> For coding i combine a certain number of packets, from ip header
>> onwards(ip header included). So when i decode i should have a packet from
>> ipheader onwards.
>>
>> void
>> Decoder::check_uncoded(Packet *p) //p is the coded packet
>> {
>>    FoundPacketsList found_pkts_list;// this is typedef of type :
>> Vector<Packet *>
>>    WritablePacket *wp = p->uniqueify();
>>   xor_header *xor_h_cod = (xor_header *)wp->data();//i have created my own
>> header
>>    int entries_cod = xor_h_cod->get_entries();
>>    int coded_hlen = xor_header::get_header_length(entries_cod);
>>    for( int i = 0; i < entries_cod; i++)
>>    {
>>        //_ddhq is a type if queue and here i am basically checking if the
>> ipid of the unocoded packet
>>       //is present in the coded header that i created
>>        int location =  _ddhq.is_present(xor_h_cod->get_entry_ipid(i));
>>        if( location >= 0 )
>>        {
>>                //if the id is in the coded header i add it to a list
>>            found_pkts_list.push_back(_ddhq.packet(location));
>>        }
>>    }
>>    if(found_pkts_list.size() > 0)
>>    {
>>
>>        bool decodable = false;
>>        //this is the condition for decodability
>>        if( entries_cod - found_pkts_list.size() == 1)
>>        {
>>            decodable = true;
>>        }
>>        //remove my header
>>        wp->pull(coded_hlen);
>>        FoundPacketsList::iterator x = found_pkts_list.begin();
>>        //here i combine the packets in the list with the coded packet to
>> decode it
>>        while( x < found_pkts_list.end())
>>        {
>>            Packet *p_i = (*x);
>>            unsigned char *xored_data = (unsigned char *)wp->data();
>>            unsigned char *data = (unsigned char *)(p_i->ip_header());
>>            int len = p_i->length();
>>            for (int i = 0; i < len; i++) {
>>                xored_data[i] ^= data[i];
>>            }
>>            x++;
>>        }
>>        if(decodable)
>>        {
>>            //wp = wp->uniqueify();
>>            click_chatter("WOOHOO Packet Decoded");
>>            click_chatter("Length: %u", wp->length());
>>
>>            click_ip *iph = wp->ip_header();
>>            //PROBLEM IS HERE ip_header() returns nothing
>>            if(!iph)
>>                click_chatter("Shitty packet"); // this is always called
>> because the iph is never created
>>            else
>>            {
>>                click_udp *udph = wp->udp_header();
>>                if(!udph)
>>                    click_chatter("UDP header not found");
>>            }
>>                //here i push the packet to the higher layers
>>                //i use a tun element for this and when i run it gives: no
>> network header as the error
>>            output(1).push(wp);
>>        }
>>
>>    }
>>    else
>>    {
>>        click_chatter("None of the packets found in uncoded queue.");
>>        _codedq.push(0,p);
>>    }
>> }
>>
>>
>>
>>
>>  Tºüçhé §übt!é
>>
>>
>>
>>
>>
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>> click at amsterdam.lcs.mit.edu
>> https://amsterdam.lcs.mit.edu/mailman/listinfo/click
>>
>
>
>