From: Gyoung-Yoon Noh <nohmad@...>
Date: 2006-07-25T13:17:54+09:00
Subject: Re: bit-struct and constructing ARP messages.

You can achieve the goal using Array#pack / String#unpack by
hand. But there are already good libraries supporting C function
calling and type conversion in Ruby: ruby-dl2[1], ruby-dlx[2].

[1]: http://rubyforge.org/cgi-bin/viewvc.cgi/ruby-dl2/doc/struct.txt?revision=1.2&root=ruby-dl2&view=markup
[2]: http://ruby-dlx.rubyforge.org/

HTH,

On 7/25/06, Kevin Waters <ooberyoozer@gmail.com> wrote:
> Hello all.
>
> I have been trying to write a ARP packet injector script for Ruby
> and did quite a bit of research on how to construct ARP Reply datagrams
> and what not, and now that I think I have an idea how to construct them
> but also I'd like to transmit them to a host.
>
> Courtesy of bit-struct I am able to craft and fill in the headers of an
> IPv4 datagram with ease, but transmitting this information is not so
> easy. What I'd like to know is is there some specific syntax using
> Socket#new for just transmitting packets not to any specific TCP port?,
> this is a snippet from the script:
>
> ------------------------------------------------------------------------------
> class IP < BitStruct
>           unsigned    :ip_v,     4,     "Version"
>           unsigned    :ip_hl,    4,     "Header length"
>           unsigned    :ip_tos,   8,     "TOS"
>           unsigned    :ip_len,  16,     "Length"
>           unsigned    :ip_id,   16,     "ID"
>           unsigned    :ip_off,  16,     "Frag offset"
>           unsigned    :ip_ttl,   8,     "TTL"
>           unsigned    :ip_p,     8,     "Protocol"
>           unsigned    :ip_sum,  16,     "Checksum"
>           octets      :ip_src,  32,     "Source addr"
>           octets      :ip_dst,  32,     "Dest addr"
>           rest        :body,            "Body of message"
>
>           note "     rest is application defined message body"
>
>           initial_value.ip_v    = 4
>           initial_value.ip_hl   = 5
> end
>
> def mk_dgram(src_ip,dst_ip,src_h,dst_h)
>         arp_msg = ['1', '0x800', '6', '4', '2', src_h, src_ip, dst_h,
> dst_ip]
>
>         ip = IP.new
>         ip.ip_tos = 0
>         ip.ip_len = 0
>         ip.ip_id  = 0
>         ip.ip_off = 0
>         ip.ip_ttl = 255
>         ip.ip_p   = 255
>         ip.ip_sum = 0
>         ip.ip_src = src_ip
>         ip.ip_dst = dst_ip
>         ip.body   = arp_msg.to_s
>         ip.ip_len = ip.length
>         puts ip.inspect_detailed
>
>         # TRANSMISSION CODE WOULD GO HERE
>         # .....
> end
> -----------------------------------------------------------------------------
>
> Now I'm stuck with transmitting this datagram, any idea how I would
> implement this?. Also I'm just taking a guess there as how to craft an
> ARP Message encapsulated in an IP datagram so if you know the correct
> way of doing that too your feedback is much appreciated.
>
> I apologize in advance if this was not an appropriate place to post this
> subject .
>
>
> --
> Posted via http://www.ruby-forum.com/.
>
>


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