newbie: need help joining lans

[Peter Lees - SE <Peter.Lees@Aus.Sun.COM>]

g'day,

i'm trying to simulate two lans joined by a duplex link, but am having
a bit of trouble.  the first packet makes it from lan A to lan B, but
never seems to get any responding packet.  i guess this is a routing
thing, but i'm at a loss to work out what's going on or how i can fix it.

the script is attached - any help would be *greatly* appreciated.

thanks

p

--
Peter Lees * Cluster Technology Consultant * Sun Microsystems Asia-Pacific
peter.lees@sun.com   *   tel: +61 2 9466 9441    *    fax: +61 2 9466 9415
## copyright disclosure: incorporates code from ns example scripts and
##                       documentation.

## setup environment #########################################################

Agent/TCP/FullTcp set segsize_ 1460
Http set TRANSPORT_ FullTcp

set ns [new Simulator]
set namfile [open "2lans.nam" w]
set log [open "2lans.log" w]
$ns namtrace-all $namfile



## create the network ########################################################

# home network
set n1 [$ns node]
set n2 [$ns node]

$ns make-lan "$n1 $n2" 10Mb 2ms LL Queue/DropTail Mac/802_3 Channel


# work network
set n3 [$ns node]
set n4 [$ns node]

$ns make-lan "$n3 $n4" 100Mb 2ms LL Queue/DropTail Mac/802_3 Channel


# dialup line from home to work
#$ns duplex-link $n2 $n3 36kb 10ms DropTail
$ns duplex-link $n2 $n3 5Mb 5ms DropTail


$ns rtproto Static $n2 $n3


## create the server & client ################################################

# use pagepool/compmath to create a compound page, which includes
# several embedded object (eg gifs, etc)

set pgpool [ new PagePool/CompMath ]
$pgpool set main_size_ 1024        ;# Size of main page =~ 1k
$pgpool set comp_size_ 5000        ;# Size of embedded object =~ 5k
$pgpool set num_pages_ 3           ;# Number of objects per compound page


# set random page lifetime (used by cache) to 100 sec
# embedded objects last forever
set tmp [new RandomVariable/Constant]
$tmp set val_ 100
$pgpool ranvar-main-age $tmp

# create the server on webserver
set server [new Http/Server/Compound $ns $n4]
$server set-page-generator $pgpool
$server log $log

set client [new Http/Client/Compound $ns $n1]
set tmp [new RandomVariable/Constant]
$tmp set val_ 10
$client set-interval-generator $tmp
$client set-page-generator $pgpool
$client log $log


## start-connection procedure ################################################

proc start-connection {} {
  global ns server  client
  $client connect $server

  # Comment out following line to continuously send requests
  $client start-session $server $server
  # Comment out following line to send out ONE request
  # DON't USE with start-session!!!
#  set pageid $server:[lindex [$client gen-request] 1]
#  $client send-request $server GET $pageid
}


## finish procedure ##########################################################

proc finish {} {
  global ns namfile client server
  $client stop-session $server
  $ns flush-trace
  close $namfile
  exec nam 2lans.nam &
  exit 0
  }



## run script ################################################################

$ns at 1.0 "start-connection"
$ns at 50.0 "finish"


$ns run