Error on custom packet creation

[Bobby, Paul]

Here is my simple program.

 

# Sending raw packets

 

seq = rand();

 

ip1 = forge_ip_packet (
        ip_hl:5,
        ip_v:4,
        ip_tos:0,
        ip_len:20,
        ip_id:69,
        ip_off:0,
        ip_ttl:200,
        ip_p:IPPROTO_TCP,
        ip_src:this_host()
        );
tcp1 = forge_tcp_packet (
        ip:ip1,
        th_sport:1234,
        th_dport:80,
        th_flags:TH_SYN,
        th_seq:seq,
        th_ack:0,
        th_x2:0,
        th_off:0,
        th_win:2048,
        th_urp:0
        );

 

send_packet(tcp1,pcap_active:FALSE);

 

When I run nasl -t target script, and sniff, the packet goes out on the wire, but ethereal decodes the packet with the following error:

 

"Bogus TCP Header length (0, must be at least 20)"

 

Indeed, if the SYN was sent to my destination on port 80, I should receive a SYN/ACK back from the destination, but nothing is received.

 

Within Nasl however, I'm unable to set the header length. It does not appear to be auto-calculated.

 

Paul