Satellite Internet Connection HOW-TO

Introduction

This document briefly explains Satellite technology, how it works, what do you need, configuration and how to sharing it between several clients. So the main focus is the Internet connection, satellite TV is not reviewed.

How does it work?

So first we make the request (using land Internet connection) to the Sat-Server usually via a tunnel, after it will retrieve out info from Internet and it will send it to Satellite; in the end we would receive data from the it to our home using a parabolic antenna and a Sat Card.

Satellite works very well with protocols, which have a little request data and a much bigger answer size. Although, a big time of answer is the biggest problem of satellite connection that may prevent using interactive services such as VoIP. The delay of answer may be considered basing on that a typical Sat distance is like 36.000 km, so an average overall delay time is 300-400 ms.

To install the little satellite system we need:

DVB-S Card
Parabolic Antenna (Satellite Dish)
LNB Digital Converter

Technical Information

A satellite link as a classical Wireless link is very different from Wired link. It may cause some additional problems to solve, such as reachability, privacy problems and so on. Also there could be weather problems, particularly in snow or rain conditions.

Antenna / Converter

A parabolic antenna gives a very high gain in RX. A frequency that is being received from the satellite transponder is from 11GHz up to 12.7 GHz. The Digital Converter transforms it to 1-2 GHz and send signal to the DVB-S card receiver through the coax cable up to 30-40m. This documents assumes that your parabolic antenna is properly mounted and calibrated as well as proper converter (usually Ku-band) is used.

DVB-S Receiver Card

DVB-S card receives analog signals via coax cable and converts it to digital signals pretty like Ethernet card, after that the OS transforms it to a TCP/IP packets.

DVB Setup

1. Install DVB-S Card and check if system recognized it

Please note, that in most cases you need PCI version 2.1 or higher (check DVB card specifications). In practice it is Pentium-III or later systems.

  # lspci | grep -i "multimedia controller"

2. Make sure that kernel modules are loaded

You have to use Alpine 1.7.10 release or higher that should load appropriate kernel modules for DVB card on startup. You may check if DVB devices are installed.

  # ls -la /dev/dvb*

3. Install LinuxTV Applications

  # apk_add linuxtv-dvb-apps

4. Create and edit file channels.conf

This file contains settings for each Satellite you are using. For example the satellite Sirius-2 Nordic Beam has the following parameters: Freq - 12322Mhz, Polarization - vertical, Symbol Rate - 27.670213Ms/s. All parameters you have to receive from ISP or find in the Internet. Please look at Satellite Parameters and SES SIRIUS. The following example is for Sirius-2 Nordic Beam:

  # echo "Sirius2-Nord:12322:v:0:27670:0:0:0" >> /etc/channels.conf

Please, note,that the satellite Sirius-2 will be off soon, Sirius-4 has been lunched instead.

5. Tune DVB Receiver

  # szap -c /etc/channels.conf -n 0

In some cases you may need to run this command permanently in background because of a bug kernel modules for some dvb cards.

  # szap -c /etc/channels.conf -n 0 > /dev/null 2>&1 &

6. Set up DVB network interface

Your ISP provides you the PID, which is used for select a transmission between many signal from same frequency.

  # dvbnet -a 0 -p $PID

  # ifconfig dvb0_0 hw ether $MAC
  # ifconfig dvb0_0 $IP up

Here $IP is any IP address, which does not match with any other adrres in your network. The $MAC you specify here is usually the MAC address of your DVB card, in some cases ISP calculates MAC address for you. In any case ISP sends data only for registered MAC addresses.

Due to nature of satellite connection, the dvb interface receives packets, which have been originated from other sources, actually ether from land internet connection interface or, in most cases, from virtual tunnel device. So in order to allow receiving such packets the source validation should be disabled on dvb0_0 interface.

  # echo "0" > /proc/sys/net/ipv4/conf/dvb0_0/rp_filter

7. Test if satellite interface is receiving data

You should see many packets for other clients of your ISP.

  # apk_add tcpdump
  # tcpdump -n -i dvb0_0

Authentication with ISP

Before you receive your data via satellite your ISP should authenticate you as their registered client. There are several common techniques could be used:

Some ISPs use the "Proxy Authentication", when you used their proxy, you also need to give login and password to continue the request. Once done, the ISP use your IP address to calculate your MAC address, to which send the answer.

Some other ISPs require you make a VPN connection (using your login and password) first, then they will control your registration account (where they retrieve your MAC address) and will send data to your card (your MAC address).

If you have static public IP, perhaps, the most convenient way is when ISPs suggest making a GRE/IPIP tunnel, which is used to sent authenticated requests to ISP satellite server. Consequently ISP sends back answers via satellite you are connected to.

Here is an example of setting up GRE tunnel with a ISP:

1. Make static routes

All queries to DNS servers of your land ISP should go via land line.

  # route add $DNS1 gw $DEFAULT_LAND_GATEWAY
  # route add $DNS2 gw $DEFAULT_LAND_GATEWAY

GRE packets should always go via land default gateway.

  # route add $SAT_ISP_GRE_IP gw $DEFAULT_LAND_GATEWAY

It is assumed that $DEFAULT_LAND_GATEWAY is default gateway given by the land ISP, $DNSx are your DNS servers provided by the land ISP and $SAT_ISP_GRE_IP is remote IP of GRE tunnel of the satellite ISP.

Changes of default route will be made after a tunnel interface is created.

2. Make GRE tunnel and setup tunnel interface

  # apk_add iproute2

  # modprobe ip_gre
  # modprobe tun

  # ip tunnel add tun0 mode gre local $MY_STATIC_IP remote $SAT_ISP_GRE_IP ttl 250
  # ifconfig tun0 $LOCAL_TUN_IP pointopoint $REMOTE_TUN_IP up

Now make new default route that goes via tunnel interface. So most requests will go via GRE tunnel to satellite ISP with source IP as $LOCAL_TUN_IP. Answers expected via dvb interface for destination IP as $LOCAL_TUN_IP.

  # route del default
  # route add default dev tun0

Parameters of a tunnel such as $SAT_ISP_GRE_IP, $LOCAL_TUN_IP, $REMOTE_TUN_IP are provided by the satellite ISP.

3. Test satellite internet connectivity

  # ping wiki.alpinelinux.org

  # tcpdump -n -i tun0
  # tcpdump -n -i dvb0_0 host $LOCAL_TUN_IP

Sharing Satellite Internet Connection

It is assumed that we need to share the satellite internet with clients in a local network that already is connected via second Ethernet interface to satellite internet machine. This requires enabling IP forwarding, set up simple SNAT masquerading and traffic filtering rules. The easiest way is to use Shorewall for that purpose.

1. Install shorewall

  # apk_add shorewall

2. Set up shorewall.conf

 IP_FORWARDING=yes
 ROUTE_FILTER=No
 CLAMPMSS=Yes # See RFC2923

3. Set up zones

  inet ipv4
  loc  ipv4
  tun  ipv4
  dvb  ipv4

4. Set up interfaces

  loc   eth1    detect   routefilter
  inet  eth0    detect   norfc1918,routefilter
  tun   tun0    -        norfc1918,routefilter
  dvb   dvb0_0  -

5. Set up policy

  loc   all  REJECT  info
  dvb   all  REJECT  info
  all   all  DROP    info

6. Set up SNAT masquerading in masq

  tun0  eth1

7. Set up params

  #This IP address are provided by the satellite ISP
  SAT_ISP_GRE_IP=
  LOCAL_TUN_IP=

7. Set up rules

  SECTION ESTABLISHED
  REJECT        dvb  fw:!$LOCAL_TUN_IP

  SECTION RELATED
  REJECT        dvb  fw:!$LOCAL_TUN_IP
 
  SECTION NEW
  DNS/ACCEPT    fw   inet
  Ping/ACCEPT   fw   inet

  #Allow Web/FTP queries via GRE tunnel to ISP
  # Answers come as RELATED/ESTABLISHED traffic via DVB
  Web/ACCEPT    fw   tun
  Web/ACCEPT    loc  tun            
  FTP/ACCEPT    fw   tun           
  FTP/ACCEPT    loc  tun            
  Ping/ACCEPT   fw   tun           
  Ping/ACCEPT   pr   tun

8. Set up tunnels

  gre  inet   $SAT_ISP_GRE_IP

Conclusion

This document reviewed just basic ideas how to setup and share satellite internet connection. Further releases of Alpine Linux will include start up and configuration scripts. Note, that more advanced traffic routing is beyond of scope of this document.

More information

Satellite Dish
Ku-band
LinuxTV Wiki
Satellite HOW-TO
IP Tunnelling HOW-TO
Satellite Parameters 
SES SIRIUS
Shorewall
Linux Advanced Routing & Traffic Control HOWTO