Connection and VPN Bonding

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Perferablly bond multiple 3G modems together to create a stable faster connection. I am trying to aggregate 3 unstable connections into one.


  • Bond 2-3 OpenVPN tun interfaces.
    • LAGG
    • Kernel Bonding
      • LACP (Stable connections, same BW)
  • Linux Advanced Routing & Traffic Control -


Custom Linux

I tested with debian. Once it get greater then two modems I will post some real results. I was able to get what I wanted working but it did not seem that much faster over the 2x 3g modems. I do not know if it was the latent speed or whatnot but we will see.

I would like to try 3 to 4 of them and really see what happends.

Server Configuration

I used a Debian VPS because I wanted to route all my traffic out to the internet through the bond.


su -
aptitude update
aptitude upgrade
aptitude install openvpn

tap configuration is a bit different then tun configuration. Since it works via layer two you do not need to worry about layer 3 stuff like IPs in the config file.

Setup a CA, Certs, ta.key: but here are some commands for reference:

mkdir /etc/openvpn/easy-rsa
cp /usr/share/doc/openvpn/examples/easy-rsa/2.0/* /etc/openvpn/easy-rsa
cd /etc/openvpn/easy-rsa/
source ./vars
./build-key-server servername
cd keys
openvpn --genkey --secret ta.key
cd ..
./build-key-pkcs12 clientx

You need some openvpn config files in /etc/openvpn/ and here is an example of a tap server openvpn config file:

proto udp
dev tap1

port 36214

ca /etc/openvpn/easy-rsa/keys/ca.crt
cert /etc/openvpn/easy-rsa/keys/server.crt
key /etc/openvpn/easy-rsa/keys/server.key
dh /etc/openvpn/easy-rsa/keys/dh1024.pem
tls-auth /etc/openvpn/easy-rsa/keys/ta.key 0

keepalive 2 10



max-clients 10
tun-mtu 1500

verb 3

cipher AES-256-CBC


#status /var/log/openvpn-status35214.log


log-append openvpn.36214.log

You need a vpn server for each modem that you want to bond. You will need to configure a different port and ip for each one while also a different tap interface.

You need to stop and disable openvpn from starting because the script will call openvpn.

/etc/init.d/openvpn stop
update-rc.d openvpn disable

Bonding Script

You also need the utilities that this script calls

aptitude install uml-utilities ifenslave

modprobe bonding mode=0 miimon=100
modprobe tun

ifconfig tap0 down
ifconfig tap1 down

tunctl -u root -g root -t tap0
tunctl -u root -g root -t tap1

ifconfig tap0 up
ifconfig tap1 up

openvpn /etc/openvpn/server1.conf &
openvpn /etc/openvpn/server2.conf &
sleep 10

ifconfig bond0 hw ether 00:11:22:33:44:55
ifconfig bond0 netmask broadcast up

ifenslave bond0 tap0 tap1

ip addr add dev tap0 scope link
ip addr add dev tap1 scope link

Take note of the 'modprobe bonding mode=0 miimon=100' line. I use zero because I would like to try and combine the BW of both modems. The bonding mode is important depending on what you would like to do:

Possible values are:

  • balance-rr or 0 - Round-robin policy: Transmit packets in sequential order from the first available slave through the last. This mode provides load balancing and fault tolerance.
  • active-backup or 1 - Active-backup policy: Only one slave in the bond is active. A different slave becomes active if, and only if, the active slave fails. The bond's MAC address is externally visible on only one port (network adapter) to avoid confusing the switch.
  • balance-xor or 2 - XOR policy: Transmit based on the selected transmit hash policy. The default policy is a simple ( {source} \oplus {destination} ) % n_{slaves} - Alternate transmit policies may be selected via the xmit_hash_policy option. This mode provides load balancing and fault tolerance.
  • broadcast or 3 - Broadcast policy: transmits everything on all slave interfaces. This mode provides fault tolerance.
  • 802.3ad or 4 - IEEE 802.3ad Dynamic link aggregation. Creates aggregation groups that share the same speed and duplex settings. Utilizes all slaves in the active aggregator according to the 802.3ad specification. (Need Switch Support)
  • balance-tlb or 5 - Adaptive transmit load balancing: channel bonding that does not require any special switch support. The outgoing traffic is distributed according to the current load (computed relative to the speed) on each slave. Incoming traffic is received by the current slave. If the receiving slave fails, another slave takes over the MAC address of the failed receiving slave. Need Switch Support)
  • balance-alb or 6 - Adaptive load balancing: includes balance-tlb plus receive load balancing (rlb) for IPV4 traffic, and does not require any special switch support. The receive load balancing is achieved by ARP negotiation.

More info here:

Cleanup Script

You will also want to cleanup the bonding script after exit or when you need to:
ip addr del dev lo
ip addr del dev tap1
ip addr del dev tap0

killall -9 openvpn

rmmod bonding
rmmod tap

Client Configuration

Configuring the modems, vpns, bonding, forwarding, to connect adn route to the vpn server.

USB Drive/Modem CD Rom Eject

I have some novatel wireless usb modems. They have built in mini sd card holders and emulated cdrom drives on them for drivers. To get them to work in linux or bsd you need to eject the drive.

The first step is to disble some settings for the usb devices in windows. You cannot get around it. I had to disable "Enable Removable Disk" and Enable CD-ROM Disk in my software card manager that I installed in windows. (VZAccess Manager)

You would think that disabling the drive would disable it all the way. It does not. You have to make the OS eject it on plugin.

The next step is to get the OS to eject the CD drive:

After you plug the device in edit /etc/udev/70-persistent-cd.rules find your device (Novatel_Mass_Storage) and add:

, RUN+="/usr/bin/eject %k"

You will have to do this for each of these type of modems.

Testing Modem with wvdial

I used wvdial to test the modem. It looks like pppd accepts .chat scripts too. Here is my wvdial conf script:

[Dialer Defaults]
Init1 = ATZ
#Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Init2 = ATQ V1 E1 S0=0 &C1 &D2 +FCLASS=0
Init3 - ATQ V1 E1 S0=0 &C1 &D2 +FCLASS=0
#? - Init5 = AT+CGDCONT=1,"IP",""
Carrier Check = yes
Dial Command = ATX1DT
Modem Type = Analog Modem
Baud = 460800
New PPPD = yes
Modem = /dev/ttyUSB0
ISDN = 0
Phone = #777
Password = JustAnyOldPW
Username =

Replace 5555555555 with your devices phone number. I cant remember what the no auth option is. It was actually working with any

ppd and chat scripts

We are going to use pppd to manage and connect to the modems.

I used the commands:

pppd updetach defaultroute usepeerdns noipdefault debug noauth asyncmap 0 ipcp-accept-local ipcp-accept-remote modem crtscts  noauth connect '/usr/sbin/chat -t5 -v -e -E -f /etc/ppp/peers/vzw_chat' 100 460800 /dev/ttyUSB0
pppd updetach defaultroute usepeerdns noipdefault debug noauth asyncmap 0 ipcp-accept-local ipcp-accept-remote modem crtscts  noauth connect '/usr/sbin/chat -t5 -v -e -E -f /etc/ppp/peers/vzw_chat' 100 460800 /dev/ttyUSB4

I put the command in a file along with an & char and they would not finish running. I have to look into it.

This is the chat script I use for verizon:

"" 	"ATZ"
OK 	'ATQ V1 E1 S0=0 &C1 &D2 +FCLASS=0'
OK 	'ATQ V1 E1 S0=0 &C1 &D2 +FCLASS=0'
SAY 	"Dialing"
OK	"ATX1DT#777"

OpenVPN on the Client

Install openvpn:

aptitude install openvpn

Disable automatic startup:

/etc/init.d/openvpn stop
update-rc.d openvpn disable

You need your ta.key and client.p12 file from the server. Get them to the client.

You need a client config for each modem:


remote 55555


dev tap1
proto udp

ping 2
ping-restart 10

resolv-retry infinite

cipher AES-256-CBC



tun-mtu 1500

pkcs12 /etc/openvpn/thenameofyourcert.p12
tls-auth /etc/openvpn/ta.key 1

ns-cert-type server


verb 3

txqueuelen 10


Once again you will have to change the tap interface number and remote server port.

Make a scripts dir in /etc/openvpn and put these two files in it:
ip addr add dev tap0
ifenslave bond0 tap0

ip addr add dev tap1
ifenslave bond0 tap1

Bonding Script

Here is the script that you will use to connect to the server and bond the taps. You will first need to install some commands called by it:

aptitude install ipcalc uml-utilities


ip route del default
ip route del default

ppp_ip0=`ip addr show ppp0 | grep inet | awk '{ print $2 }'`
ppp_ip1=`ip addr show ppp1 | grep inet | awk '{ print $2 }'`
ppp_pip0=`ip addr show ppp0 | grep inet | awk '{ print $4 }'`
ppp_pip1=`ip addr show ppp1 | grep inet | awk '{ print $4 }'`
ppp_gwip0=`ipcalc "$ppp_pip0" | grep Address | awk '{ print $2 }'`
ppp_gwip1=`ipcalc "$ppp_pip1" | grep Address | awk '{ print $2 }'`

echo "$ppp_ip0"  "$ppp_ip1"  "$ppp_pip0"  "$ppp_pip1"  "$ppp_gwip0"  "$ppp_gwip1" 

ip route add "$ppp_gwip0" dev ppp0 src "$ppp_ip0" scope link table 100
ip route add "$ppp_gwip1" dev ppp1 src "$ppp_ip1" scope link table 101
ip route add default via "$ppp_gwip0" dev ppp0 table 100
ip route add default via "$ppp_gwip1" dev ppp1 table 101
ip rule add from "$ppp_ip0" table 100 prio 20000
ip rule add from "$ppp_ip1" table 101 prio 20001

modprobe bonding mode=0 miimon=100
modprobe tun

tunctl -d tap0
tunctl -d tap1

echo  "$ppp_ip0" "$ppp_ip1"
openvpn --config /etc/openvpn/client.21456.conf --local "$ppp_ip0" --script-security 2 --up /etc/openvpn/scripts/ &
openvpn --config /etc/openvpn/client.21466.conf --local "$ppp_ip1" --script-security 2 --up /etc/openvpn/scripts/ &

ifconfig bond0 hw ether 55:44:33:22:11:00
ifconfig bond0 netmask broadcast up

ip route add default via dev bond0

Edit it with your openvpn config file locations.

Cleanup Script

To clean the client vpn/routes/bond:

ip addr del dev lo
ip addr del dev tap1
ip addr del dev tap0

killall -9 openvpn
killall -9 openvpn

ppp_ip0=ip addr show ppp0 | grep inet | awk '{ print $2 }'
ppp_ip1=ip addr show ppp1 | grep inet | awk '{ print $2 }'

ip addr del "$ppp_ip0" dev ppp0
ip addr del "$ppp_ip1" dev ppp1

killall -9 pppd
killall -9 pppd

#Still need a way te reset the modems
#pccardctl eject
#pccardctl insert

ip route flush table 100
ip route flush table 101

rmmod bonding
rmmod tap

NAT Forwarding as Internet Gateway

The entire reason I wanted to do this was to forward internet traffic through multiple modems. So on my debian box:

nano /etc/sysctl.conf

Uncomment: #net.ipv4.ip_forward=1

echo 1 > /proc/sys/net/ipv4/ip_forward

You then can forward incoming traffic with:

iptables -t nat -A POSTROUTING -o bond0 -j MASQUERADE

And put the line in it so we can call the file later when we want.

On the server you want to forward traffic from bond0 and on the client from whatever interface your want to share from/turn into a gateway.

If you use ufw you will need to do it in the ufw files.



  • With the USB760 modem you need to eject the drive before it works.
cdcontrol -f /dev/cd0

This needs to be automated. This thread suggests a devd rule:,43285.0.html

bsd router/firewall/more

The modem worked great once I ejected it. I did not see the type of bonding I wanted. I am 99% sure this can do layer 3 loadbalancing though.

I did not go further atm.

  • With the UML290:
    • the dial command is not #777 but instead *99***3#
    • Username is:
    • Password is: vzw



Zeroshell is a Linux distribution for servers and embedded devices aimed at providing the main network services a LAN requires. It is available in the form of Live CD or Compact Flash image and you can configure and administer it using your web browser.

  • Says it supports VPN Bonding
  • 3G support (+It is linux)

I was able to get ZeroShell to work. It has a nice interface but is made to be run off a live cd. I need the flexibility of a custom router.

To get my modem to work I had to move the eject command from a 32bit fedora rpm to the system.

ZeroShell does vpn bonding just like the one that I made in this artical.


udev/cdcontrol Creation