Networking with UMLs -- Robert McCabe, Spring 2008

It is possible to do lab2b with only two machines.  This is my setup::

____Machine #10___   
|   _____        |    	
|   |UML1|       |
|   |.180|       |
|     |          |            Machine    
|   __|__        |            _#11__
|   |UML2|       |            |    |
|   |.181|---.254|.10 ----.11 |    |
|________________|            |____|

On Machine #10 I have two uml's running UML1 is the kernel that will capture the
TCP statistics.  UML2 is the kernel that is running the modified version of 
ip_forward.c (to drop packets in a deterministic manner).  Machine #11 is simply the sink of the sock program.

Unfortunately, to get UML1 to route through UML2 (and not directly to the .254 interface) takes some work.  Here are the steps:

First on the host machine configure the tap0 interface to allow multiple
uml instances (otherwise each uml gets its own tap interface -- which effectively
acts as a point-to-point link):

machine10-host#  uml_switch -tap tap0 -unix /tmp/umlsw -daemon

This will start a background process called uml_switch.

Manually bring up the tap0 interface and do the book-keeping normally
done by the uml_utilities:

machine10-host# ifconfig tap0 192.168.0.254 netmask 255.255.255.0 up
machine10-host# echo 1 > /proc/sys/net/ipv4/ip_forward
machine10-host# route del -net 192.168.0.0 dev tap0 netmask 255.255.255.0
machine10-host# route add -host 192.168.0.181 dev tap0
machine10-host# route add -net 192.168.0.176 dev tap0 netmask 255.255.255.240 gw 192.168.0.181
machine10-host# echo 1 > /proc/sys/net/ipv4/conf/tap0/proxy_arp
machine10-host# arp -Ds 192.168.0.181 eth0 pub



Start your two uml instances:

machine10-host#  ./linux_tcp_show ubd0=root_fs_cow1,root_fs umid=uml1 mem=128M eth0=daemon,,unix,/tmp/umlsw
machine10-host#  ./linux_drop_pkt ubd0=root_fs_cow2,root_fs umid=uml2 mem=128M eth0=daemon,,unix,/tmp/umlsw



In both UML1 and UML2 do:

uml1&2# for f in /proc/sys/net/ipv4/conf/*/*redirects; do echo 0 > $f;done 

(without this UML2 will send back "route re-direct" messages to UML1 and UML1
will start to route directly to .254)

you need to restart the network for setting to take effect

uml1&2# /etc/rc.d/init.d/network restart

Set up routing table in uml1:

ifconfig eth0 192.168.0.180
route del -host 192.168.0.254 dev eth0
route del default gw 192.168.0.254
route del -net 192.168.0.0 dev eth0 netmask 255.255.255.0
route add -host 192.168.0.181 dev eth0
route add default gw 192.168.0.181

set up routing table in uml2:

ifconfig eth0 192.168.0.181
route del -net 192.168.0.0 dev eth0 netmask 255.255.255.0
route add -host 192.168.0.254 dev eth0
route add -host 192.168.0.180 dev eth0
route add default gw 192.168.0.254
echo 1 > /proc/sys/net/ipv4/ip_forward 

Give machine #11 a route to UML1
machine11# route add -host 192.168.0.180 gw 192.168.0.10 dev eth0

IP address : 192.168.0.180
IP network number : 3019942080
IP address : 192.168.0.254
IP network number : 4261456064