http://www.balabit.com/download/files/tproxy/

Apa sih arti arti 'proxy'?
--------------------------------

Proxy adalah program yang menyerupai server, menerima permintaan dari klien lalu meneruskan permintaan tadi ke server sebenarnya yang diinginkan pengguna dan mengirim kembali hasilnya begitu diterima.
Proxy membaca dan mengartikan protokol aplikasi dan menolak lalulintas yang tidak diinginkan. Seperti kebanyakan serangan pada protokol aplikasi, tidak menginjinkan pelanggaran pada protokol biasanya melindungi terhadap serangan.

What is transparent proxying?
-----------------------------
Untuk menyederhanakan tugas managemen klien yang berada dibelakang firewall proxy
firewalls, teknik 'transparent proxying' perlu dipikirkan.
Transparent proxy berarti keberadaan proxy tidak kelihatan oleh user. Transparent Proxy sendiri membutuhkan dukungan kernel.

We have a 'REDIRECT' target, isn't that enough?
----------------------------------------------

Real transparent proxying requires the following three features from
the IP stack of the computer it is running on:
1. Redirect sessions destined to the outer network to a local process
using a packet filter rule.
2. Make it possible for a process to listen to connections on a
foreign address.
3. Make it possible for a process to initiate a connection with a
foreign address as a source.

Item #1 is usually provided by packet filtering packages like
Netfilter/IPTables, IPFilter. (yes, this is the REDIRECT target)

All three were provided in Linux kernels 2.2.x, but support for this
was removed.

How to install it?
------------------

Download the latest tproxy-kernel-*.tar.bz2 tarball
for your kernel (from v2.6.24), with the tproxy-iptables-*.patch file.

Patch your kernel using:

cd /usr/src/linux
cat /00*.patch | patch -p1

then enable tproxy support, `socket' and `TPROXY' modules
(with optional conntrack support if you need SNAT), compile your kernel
and modules.

The required modules are automatically loaded if the iptables commands
are used.

The IPtables patches:

cd /usr/src/iptables-1.4.X
cat /tproxy-iptables*.patch | patch -p1

then compile it on the usual way:

./autogen.sh
./configure && make && make install

Squid-3 has official support of TProxy v4.1:

checkout the source code of squid-3 as in

http://wiki.squid-cache.org/Squid3VCS

then compile it:

cd ~/source/squid
./bootstrap.sh
./configure --enable-linux-netfilter && make && make install

Of course you might need to change the path in the examples above.

How to start using it?
----------------------

This implementation of transparent proxying works by marking packets and
changing the route based on packet mark. The foreign address bind and tproxy
redirection is enabled via a new socket option, IP_TRANSPARENT, without it
neither the bind nor the tproxy target works.

Now let's see what happens when a proxy tries to use the required tproxy
features I outlined earlier.

1. Redirection

This is easy, as this was already supported by iptables. Redirection is
equivalent with the following nat rule:

iptables -t nat -A PREROUTING -j DNAT --to-dest --to-port

is one the IP address of the interface where the packet
entered the IP stack
is the port where the proxy was bound to

To indicate that this is not simple NAT rule, a separate target, 'TPROXY'
was created:

iptables -t mangle -A PREROUTING -p tcp --dport 80 -j TPROXY --on-port \
--tproxy-mark 0x1/0x1

The local IP address is determined automatically, but can be overridden
by the --on-ip parameter.

The marked sockets has to be routed locally:

ip rule add fwmark 1 lookup 100
ip route add local 0.0.0.0/0 dev lo table 100

2. Listening for connections on a foreign address

There are protocols which use more than a single TCP channel for
communication. The best example is FTP which uses a command channel for
sending commands, and a data channel to transfer the body of files. The
secondary channel can be established in both active and passive mode,
active meaning the server connects back to the client, passive meaning
the client connects to the server on another port.

Let's see the passive case, when the client establishes a connection to
the address returned in the response of the PASV FTP command.

As the presence of the proxy is transparent to the client, the target
IP address of the secondary channel (e.g. the address in the PASV
response) is the server (and not the firewall) and this connection must
also be handled by the proxy.

The first solution that comes to mind is to add a a TPROXY rule
automatically (e.g. to redirect a connection destined to a given server
on a given port to a local process), however it is not feasible, adding
rules on the fly should not be required as it would mess the
administrator's own rules, the NAT translation should be done
implicitly without touching the user rulebase.

To do this on a Linux 2.2 kernel it was enough to call bind() on a
socket with a foreign IP address, and if a new connection to the given
foreign IP was routed through the firewall the connection was
intercepted. This solution however distracted the core network kernel
hackers and removed this feature. This implementation is similar to
the old behaviour although it works a bit differently:

* the proxy sets the IP_TRANSPARENT socket option on the listening
socket
* the proxy then binds to the foreign address
* the proxy accepts incoming connections

It requires additional iptables rules with the socket module of the
tproxy patches:

iptables -t mangle -N DIVERT
iptables -t mangle -A PREROUTING -p tcpo -m socket -j DIVERT
iptables -t mangle -A DIVERT -j MARK --set-xmark 0x1/0xffffffff
iptables -t mangle -A DIVERT -j ACCEPT

the best if the second rule is before using the TPROXY target.

3. Initiating connections with a foreign address as a source

Similarly to the case outlined above, it is sometimes necessary to be
able to initiate a connection with a foreign IP address as a source.
Imagine the active FTP case when the FTP client listens for connections
with source address equal to the server. Another example: a webserver
in your DMZ which does access control based on client IP address. If
the proxy could not initiate connections with foreign IP address, the
webserver would see the inner IP address of the firewall itself.

In Linux 2.2 this was accomplished by bind()-ing to a foreign address
prior calling connect(), and it worked. In this tproxy patch it is done
somewhat similar to the case 2 outlined above.

* the proxy calls setsockopt with IP_TRANSPARENT

* the proxy bind to a foreign address

* the tproxy calls connect()

The iptables rules with the socket match are also required here.

How to use it?
--------------

The following use-case assumes a transparent proxy listening on port
50080 and any ip address (0.0.0.0).

First, set up the routing rules with iproute2:

ip rule add fwmark 1 lookup 100
ip route add local 0.0.0.0/0 dev lo table 100

Or, if you want to use packet marking for anything else, the least
significant bit is enough for transparent proxying.

ip rule add fwmark 0x1/0x1 lookup 100
ip route add local 0.0.0.0/0 dev lo table 100

Note that this latter example is only working with newer versions of
iproute2.

For supporting foreign address bind, the socket match is required with
packet marking:

iptables -t mangle -N DIVERT
iptables -t mangle -A PREROUTING -p tcp -m socket -j DIVERT

# DIVERT chain: mark packets and accept
iptables -t mangle -A DIVERT -j MARK --set-mark 1
iptables -t mangle -A DIVERT -j ACCEPT

The last rule is for diverting traffic to the proxy:

iptables -t mangle -A PREROUTING -p tcp --dport 80 -j TPROXY \
--tproxy-mark 0x1/0x1 --on-port 50080

If it is a Squid-3 proxy, in /etc/squid/squid.conf the following
rule is necessary for transparent proxying:

http_port 50080 tproxy transparent

Then set up the ACL rules according to your local policy.

Saat ini, sy menggunakan Ubuntu ME 8.04.1, Sierra AirCard 875 dan NM versi 0.6.6

Yuk, mulai...

1. Klik pada applet Network Manager yg ada pada systray, lalu pilih Manual Configuration.
2. Unlock, lalu pilih Point to Point Connection. klok ganda atau klik Properties.

3. Check pada Enable This Connection, lalu pilih GPRS/UMTS pada menu drop down Connection Type.

4. Ketikkan APN provider pada Access Point Name. misalnya flash, Indosatm2, indosatgprs.
5. Pada tab General, masukkan user-id dan password account yang anda miliki.
6. Pada tab Modem, masukkan identitas modem yg bisa diketahui dengan cara :

 $ sudo wvdialconf
.....
Found a modem on /dev/ttyUSB0.
Modem configuration written to /etc/wvdial.conf.
ttyUSB0: Speed 9600; init "ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0"

7. Pada tab Options, biasanya dua pililhan teratas yang di check list. Setelah itu klik OK.

8. Alt-F2 >> gksu gedit /etc/chatscripts/ppp0
Edit >> *99***1#
menjadi >> *99#
Save, lalu keluar.
9. Alt-F2 >> gksu gedit /etc/ppp/peers/ppp0
Tambahkan >> connect "/usr/sbin/chat -v -f /etc/chatscripts/ppp0" #pada baris paling atas
Save, lalu keluar.
10. buka terminal, lalu

$ <del datetime="00">sudo su</del></del>
<del datetime="00"># echo “username_anda * password_anda” &gt;&gt; /etc/ppp/pap-secrets
# echo “username_anda * password_anda” &gt;&gt; /etc/ppp/chap-secrets</del>
<del datetime="00"># exi</del>t

11. Sebelum memulai koneksi, coba restart GDM dengan menekan Ctrl+Alt+Backspace. Re-Login. Untuk mulai koneksi, klik applet Network Manager -- Dial Up Connections -- connect to ...

Silahkan bandingkan proses koneksinya dengan menggunakan Wvdial... Selamat berbroadband!