Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

I want to send packets to 127.0.0.1:11311 with packETH. However, there are some problems I cannot solve.

Here's some screenshots: (click to zoom in)

enter image description here

enter image description here


  1. In IPv4 data ("Header length")

    Header length of the packets I want to send is 20. However the "Header length" only accepts a one digit number. How can I solve this kind of problem?

  2. The packets I want to send didn't specify "TOS"(In IPv4 data) & "urgent pointer"(In TCP data)

    Are these two arguments important when sending TCP packets?

  3. In IPv4 data ("options 0x")

    The TCP data options of the packets I want to send is 0x12. However it kept showing an error message:

    Wrong length of tcp options field(length mod 8 must be 0)

    0x12 mod 8 should be zero, I also tried 0x08, 0x00...etc but the error message didn't change.

    I have no idea why this happens, is it relevant to "Header length"?

share|improve this question
    
The error tells you that the options field must be multiple of 8's. In most cases the TCP packet is 20 bytes with no options field. –  0xab3d Apr 21 '12 at 18:25

1 Answer 1

up vote 0 down vote accepted
  1. The IPv4 header length field is interpreted as multiples of 4 octets. IPv4 headers are almost always 20 octets long, so this field's value is almost always 5.

  2. Nope, the TOS/DiffServ bits and urgent pointer are usually not important.

  3. This field is looking for a value, not a length. When you entered 0x12 or 0x08 or 0x00 thinking you were entering a length, you were actually just entering a single octet value. 1 mod 8 != 0. I'm guessing the packet you were trying to mimic had a 12-octet TCP Timestamp value in there. Also note that the TCP Timestamp option needs to be aligned on a 4-byte boundary from...the start of the TCP headers, if I recall correctly..., so you might need to put some one-octet 0x00 "Nop"/No-op TCP options in there as well, depending on how things align.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.