1. Ether TAP and Ether TUN

these notes came from the NSTX Debian GNU/Linux and the ULM (user mode linux configuration)
is a package which provides pseudo devices which allow a user program to read/write Ethernet packets
more than this it allows the sysadmin to configure an ethertap device to deliver all Ethernet packets destined for an IP address to a device, ie ( /dev/tap0 )
- which in turns means a user level program can read all these packets
- and it allows a user program to write these packets to the /dev/tun0
the user level program can therefore manipulate these Ethernet packets and provide:
- encryption of all Ethernet packets
- tunnelling Ethernet packets over another protocol (say DNS)

2. Configuring TUN and TAP under GNU/Linux

create the device with tunctl (available from the UML (user mode linux) utilities
```
tunctl -u uid
```
uid is the user id or username that UML will be run as
- it will tell you what device was created (assume tap0 )
now configure the device /dev/tap0 to have the IP address 192.168.0.1
```
ifconfig tap0 192.168.0.1 up
```
now enable IP forewarding

bash -c ’echo 1 > /proc/sys/net/ipv4/ip_forward’

bash -c ’echo 1 > /proc/sys/net/ipv4/conf/tap0/proxy_arp’
arp -Ds 192.168.0.2 eth0 pub
chmod 666 /dev/net/tun

now you should be able to ping 192.168.0.2
- you will have to have configured the server 192.168.0.2 in the same way

is a package which, under GNU/Linux, provides IP tunnelling over DNS
to configure this package requires that you have also installed the TUN/TAP package
- and have configured the ethertap on one machine to 192.168.0.1 and the ethertap on the other machine to 192.168.0.2
now a net route must be created through the ethertap on both sides
- see configuring TUN and TAP
now the server is started by:
```
./nstxd your.domain.name.net
```
and the client on your wireless laptop

./nstxcd your.domain.name.net 111.222.333.444

where 111.222.333.444 is the default DNS server which is expected to be used in the network connecting to your wireless laptop
it should be possible to ping 192.168.0.2 from 192.168.0.1 and the other way round

Network attacks occur at many different protocol layers. Choose 3 network protocol example attacks (two at the transport layer and one from the IP layer) and clearly show with the aid of a diagram how these attacks can be mounted.
Critically analyse appropriate countermeasures for such attacks.

For the discussion on DNS
- TCP/IP Illustrated, Volume 1: The Protocols, Addison-Wesley, 1994, ISBN 0-201-63346-9.
For security on various protocols see
- 802.11 Security By Bruce Potter, Bob Fleck 1st Edition December 2002 ISBN: 0-596-00290-4 192 pages
- 802.11 Security
IP over DNS
Secure shell
Python resource

This document was produced using groff-1.21.