Very Computer

Hi,

I need to prototype sone networking software.  Since I can pick how
and where this is done, I'm choosing FreeBSD 2.2.1

First, I need to be able to send and receive my own "layer 3" packets
but continue to use the FreeBSD IP.  Put simply, I want to replace
TCP and UDP with my own.  What is the proper way to do this?  Is it
even possible?

Second, I need to put my own 802.2 packets (ie. no IP layer) for my
own "layer 2" on the LAN.  What is the proper way to do this?

In both cases, I need the OS transparently pass thru what I'm sending
and receiving (if possible.)  I've looked thru Stevens "Unix Network
Programming", the sockets FAQ and briefly at the sources.  I've a
feeling the sources will be the only way, so I'm looking for help
on where to look first.

For my own "layer 3":
I've looked at: socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) a bit, since
"ping" lets one build their own ICMP header and the OS will prefix
what I send with the IP header.  Should this be used?  It doesn't
"feel right" as the protocol I'm using is not ICMP.

I've also considered: socket(PF_INET, SOCK_RAW, IPPROTO_RAW)
but I'm _guessing_ that this would be the way to send/rcv directly
on the wire myself (ie. build my own "layer 2").

Thanks for any help, pointers etc.

MikeC

--
Michael C. Cambria                          Voice: 617 643 6250
Systems & Communications Sciences, Inc.       Fax: 617 643 6251

Arlington, Ma. 02174                   CompuServe: 71552,2531

Quote:> Hi,

> I need to prototype sone networking software.  Since I can pick how
> and where this is done, I'm choosing FreeBSD 2.2.1

> First, I need to be able to send and receive my own "layer 3" packets
> but continue to use the FreeBSD IP.  Put simply, I want to replace
> TCP and UDP with my own.  What is the proper way to do this?  Is it
> even possible?

I've just put Ari Suutaris natd program in the ports collection at
ftp://ftp.freebsd.org/pub/FreeBSD/FreeBSD-current/ports/net/natd.
It uses divert sockets.  The man page is about to be added.  If
you want it now, give me a shout, but it's not very technical.

Quote:> Second, I need to put my own 802.2 packets (ie. no IP layer) for my
> own "layer 2" on the LAN.  What is the proper way to do this?

Quote:> In both cases, I need the OS transparently pass thru what I'm sending
> and receiving (if possible.)  I've looked thru Stevens "Unix Network
> Programming", the sockets FAQ and briefly at the sources.  I've a
> feeling the sources will be the only way, so I'm looking for help
> on where to look first.

> For my own "layer 3":
> I've looked at: socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) a bit, since
> "ping" lets one build their own ICMP header and the OS will prefix
> what I send with the IP header.  Should this be used?  It doesn't
> "feel right" as the protocol I'm using is not ICMP.

> I've also considered: socket(PF_INET, SOCK_RAW, IPPROTO_RAW)
> but I'm _guessing_ that this would be the way to send/rcv directly
> on the wire myself (ie. build my own "layer 2").

Quote:

> Thanks for any help, pointers etc.

> MikeC

Quote:> Second, I need to put my own 802.2 packets (ie. no IP layer) for my
> own "layer 2" on the LAN.  What is the proper way to do this?

  http://www.serc.rmit.edu.au/~tobbe/bpf_drv.c

/Tobbe
+---------------------------------------------------+
| Torbj?rn T?rnkvist , tel: +61 3 9282 2410         |

| WWW:   http://www.serc.rmit.edu.au/~tobbe         |
+---------------------------------------------------+

Daring to challenge the will of the almighty Leviam00se, Michael C. Cambria

: Hi,

: I need to prototype sone networking software.  Since I can pick how
: and where this is done, I'm choosing FreeBSD 2.2.1

: First, I need to be able to send and receive my own "layer 3" packets
: but continue to use the FreeBSD IP.  Put simply, I want to replace
: TCP and UDP with my own.  What is the proper way to do this?  Is it
: even possible?

: Second, I need to put my own 802.2 packets (ie. no IP layer) for my
: own "layer 2" on the LAN.  What is the proper way to do this?

I think the answer to both these questions is: the Berkeley Packet Filter
(BPF). If you have a) an ethernet card that supports it, and b) have it
configured into your kernel, BPF will let you read raw frames right off
the ethernet card and transmit them as well. I would also look at libpcap,
which uses BPF internally (libpcap is used by tcpdump). One example program
that uses BPF for receiving and tranmitting is rarpd; it needs to receive
and send ETHERTYPE_REVARP frames directly.

The only problem with BPF is that programming it can be tricky; you can
set up instructions to have BPF capture only certain packets with features
that you're interested in. This will cut down on the amount of processing
your program has to do: you can receive all packets that arrive at the
interface if you want, but then your own program will have to analyze them
and decide whether or not they're important.

-Bill

--
=============================================================================
-Bill Paul            (212) 854-6020 | System Manager, Master of Unix-Fu


=============================================================================
  "Now, that's "Open" as used in the sentence "Open your wallet", right?"
=============================================================================

Quote:> The only problem with BPF is that programming it can be tricky;

        Rich Stevens

Quote:> Second, I need to put my own 802.2 packets (ie. no IP layer) for my
> own "layer 2" on the LAN.  What is the proper way to do this?

Quote:

> For my own "layer 3":
> I've looked at: socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) a bit, since
> "ping" lets one build their own ICMP header and the OS will prefix
> what I send with the IP header.  Should this be used?  It doesn't
> "feel right" as the protocol I'm using is not ICMP.

Quote:> I've also considered: socket(PF_INET, SOCK_RAW, IPPROTO_RAW)
> but I'm _guessing_ that this would be the way to send/rcv directly
> on the wire myself (ie. build my own "layer 2").

Simply open a socket as such:

sockd = socket(AF_INET,SOCK_RAW,IPPROTO_TCP);

you then should only be writing the tcp header + data.

Mind you this doesnt work on all systems, if IP_HDRINCL is not present it
could mean that its always included, or never included. Your better off
using a modern interface to the lower level network layer like
DLPI, BPF, NIT etc etc.

 -shadows