Re: [ns] Linux TCP/IP Stack Modifications

[Eric Weigle <ehw@lanl.gov>]

Good morning-

The only way this is relevant to the ns mailing list is if you are referring to
ns running on linux, or asking if the tcp implementation in ns correlates to
that of linux.

In the first case, I suggest you look at the files tcp.cc and tcp.h in your ns
directory, you are interested in the maxrto_ variable (search for "rto" in the
files). You can also alter this variable from your tcl scripts by $tcp set
maxrt_ <value>.

In the second case, no. Real implementations (such as linux) usually do some
weird stuff to get it all to work.

If you're asking a question totally unrealated to ns and the list topic, I would
ask that you find a more appropriate forum, such as the linux kernel networking
mailing list (linux-net@vger.kernel.org, subscribe by sending an email
containing "subscribe linux-net linuxdj@lycos.com" to
majordomo@vger.kernel.org).

But, in this case, here are a few quick pointers to help you anyway: First, you
will need kernel source (see www.kernel.org to find it for your architecture,
you may also already have it installed in /usr/src/linux/). Once you get that,
look in the net/ipv4/ directory of said kernel source, where there are several
files concerning tcp. The relevant headers are include/linux/tcp.h and
include/net/sock.h. You are interested in the rto field in the tcp_opt structure
defined in sock.h, and the places it is altered by the c files in
(net/ipv4/tcp*.c). To alter this variable, you will need to edit these files as
appropriate, and recompile your kernel (you need root access to do this). Refer
to documentation at places like
www.redhat.com/mirrors/LDP/HOWTO/Kernel-HOWTO.html, www.linuxdoc.org, or the
before mentioned www.kernel.org.


Thanks,
-Eric

--------------------------------------------
 Eric H. Weigle   CCS-1, RADIANT team
 ehw@lanl.gov     Los Alamos National Lab
 (505) 665-4937   http://home.lanl.gov/ehw/
--------------------------------------------