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Configuring Linux routing for use with multi link MLVPN¶

Introduction¶

This short guide will try to help you configure linux for multi-link routing.

MLVPN will need to have a way to communicate from one end to the other using multiple links in order to aggregate them.

Example case¶

                                                       128.128.128.128
                                                      +---------------+
                                         +----------->| Fast internet |--> OUT
                                         |            +---------------+
                      mlvpn0: 10.42.42.1 |
                            +------------+-+
                  +-------->| MLVPN server |<--------+
                  |         +--------------+         |
                  |             ^      ^             |
                  |             | T  A |             |
            +-----+------+      | U  G |      +------+-----+
            |   ADSL 1   |      | N  G |      |   ADSL 2   |
            +------------+      | /  R |      +------------+
            192.168.1.1/24      | T  E |      192.168.2.1/24
                  ^             | A  G |             ^
                  |             | P  A |             |
                  |             |    T |             |
                  |             |    E |             |
       internet 1 |             |    D |             | internet 2
                  |             v      v             |
                  |         +---+------+---+         |
                  +---------| MLVPN client |---------+
                            +--------------+
                   mlvpn0: 10.42.42.2 eth0: 192.168.0.1
                                   ^
   +------+                        |
   | LAN  |------------------------+
   +------+
192.168.0.0/24

In this setup we have multiple machines:

  • MLVPN server which has a fast internet connection (100Mbps).
    • Public IP Address: 128.128.128.128/32
    • Private mlvpn IP address: 10.42.42.1/30
  • ADSL 1 router LOCAL IP address 192.168.1.1/24
  • ADSL 2 router LOCAL IP address 192.168.2.1/24
  • Local AREA network (where your standard “clients” are) on 192.168.0.0/24
  • And finally our MLVPN client router:
    • Private IP address 192.168.1.2/24 to join ADSL1
    • Private IP address 192.168.2.2/24 to join ADSL2
    • Private IP address 192.168.0.1/24 for LAN clients
    • Private IP address 10.42.42.2/30 on mlvpn0.

Yeah seems a bit complicated, but that’s not that hard after all, we just have 4 routers.

Testing the basic configuration¶

At this time from “MLVPN client” you should be able to ping 192.168.2.1 and 192.168.1.1.

You should be able to access the internet using both links.

You can test it using standard routing.

Before we do anything: (Note: you may require installing iproute2)

root@mlvpnclient:~# ip route show
default via 192.168.1.1 dev eth0
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.1
192.168.1.0/24 dev eth0  proto kernel  scope link  src 192.168.1.2
192.168.2.0/24 dev eth0  proto kernel  scope link  src 192.168.2.2

This routing table means every packet to the internet will go thru 192.168.1.1. We can test it:

root@mlvpnclient:~# ping -n -c2 -I192.168.1.2 ping.ovh.net
PING ping.ovh.net (213.186.33.13) 56(84) bytes of data.
64 bytes from 213.186.33.13: icmp_req=1 ttl=51 time=42.1 ms
64 bytes from 213.186.33.13: icmp_req=2 ttl=51 time=41.7 ms

Ok I started to use “-I192.168.1.2” here. That’s not mandatory in this example, but this will become handy later.

“-I” means we tell the ping command to use 192.168.1.2 as source address of the packets we are sending to ping.ovh.net.

Now, we know our ADSL1 link is working properly.

Testing the second link will need us to modify the routing table.

root@mlvpnclient:~# ip route add 213.186.33.13 via 192.168.2.1
root@mlvpnclient:~# ip route show
default via 192.168.1.1 dev eth0
213.186.33.13 via 192.168.2.2 dev eth0
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.1
192.168.1.0/24 dev eth0  proto kernel  scope link  src 192.168.1.2
192.168.2.0/24 dev eth0  proto kernel  scope link  src 192.168.2.2

Notice the new 213.186.33.13 (ping.ovh.net) added to the routing table.

Again, we can test the link:

root@mlvpnclient:~# ping -n -c2 -I192.168.2.2 ping.ovh.net
PING ping.ovh.net (213.186.33.13) 56(84) bytes of data.
64 bytes from 213.186.33.13: icmp_req=1 ttl=51 time=62.4 ms
64 bytes from 213.186.33.13: icmp_req=2 ttl=51 time=61.1 ms

Noticed we changed the source address, and the latency is higher on ADSL2 by ~ 20ms.

Everything is fine, let’s cleanup the routing table:

root@mlvpnclient:~# ip route del 213.186.33.13

Configuring the source routing¶

Concepts¶

Now you have two internet access, one fast internet access on the server side, but you have only one IP address on this server... How can you use your multiple ADSL links at the same time ?

That’s fairly simple, but a bit complicated to setup. It’s called “source routing”.

Source routing means the kernel will take the decision to route a packet not only based on it’s destination (like we have done just before), but also from where it came.

In our example, we want a packet coming from 192.168.2.2 to go thru ADSL 2 and a packet from 192.168.1.2 to go thru ADSL1. Simple yah?

Let’s configure it¶

First, you need to create multiple routing tables in the kernel.

That’s better to name them, so yo do it by modifing /etc/iproute2/rt_tables.

root@mlvpnclient:~# echo 101 adsl1 >> /etc/iproute2/rt_tables
root@mlvpnclient:~# echo 102 adsl2 >> /etc/iproute2/rt_tables

Your configuration file should now look like this

root@mlvpnclient:~# cat /etc/iproute2/rt_tables
#
# reserved values
#
255 local
254 main
253 default
0   unspec
#
# local
#
#1  inr.ruhep
101 adsl1
102 adsl2

We have “named” two new routing tables, but we did not create them. /etc/iproute2/rt_tables file is optional.

We must add some routes to each table to activate them.

# Inserting routes in the adsl1 table
ip route add 192.168.1.0/24 dev eth0 scope link table adsl1
ip route add default via 192.168.1.1 dev eth0 table adsl1

# Inserting routes in the adsl2 table
ip route add 192.168.2.0/24 dev eth0 scope link table adsl2
ip route add default via 192.168.1.1 dev eth0 table adsl1

# ip rule is the source routing magic. This will redirect
# packets coming from source "X" to table "adsl1", "adsl2" or "default".
ip rule add from 192.168.1.0/24 table adsl1
ip rule add from 192.168.2.0/24 table adsl2

I’ve stripped root@machine for you, so you can copy paste ;-)

Testing¶

First, show me your configuration! The first thing you should always do is displaying ip rules. (Which routing table will be used when ?)

(Please note rules are applied in order from 0 to 32767)

root@mlvpnclient:~# ip rule list
  0:      from all lookup local
  32764:  from 192.168.1.0/24 lookup adsl1
  32765:  from 192.168.2.0/24 lookup adsl2
  32766:  from all lookup main
  32767:  from all lookup default

Then the routing tables:

root@mlvpnclient:~# ip route show table adsl1
  192.168.1.0/24 dev eth0  scope link
  default via 192.168.1.1 dev eth0
root@mlvpnclient:~# ip route show table adsl2
  192.168.2.0/24 dev eth0  scope link
  default via 192.168.2.1 dev eth0
root@mlvpnclient:~# ip route show table main
  default via 192.168.1.1 dev eth0
  213.186.33.13 via 192.168.2.2 dev eth0
  192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.1
  192.168.1.0/24 dev eth0  proto kernel  scope link  src 192.168.1.2
  192.168.2.0/24 dev eth0  proto kernel  scope link  src 192.168.2.2

Ping test

root@mlvpnclient:~# ping -c2 -n -I192.168.1.1 ping.ovh.net
PING ping.ovh.net (213.186.33.13) 56(84) bytes of data.
64 bytes from 213.186.33.13: icmp_req=1 ttl=51 time=40.6 ms
64 bytes from 213.186.33.13: icmp_req=2 ttl=51 time=41.5 ms

root@mlvpnclient:~# ping -c2 -n -I192.168.2.1 ping.ovh.net
PING ping.ovh.net (213.186.33.13) 56(84) bytes of data.
64 bytes from 213.186.33.13: icmp_req=1 ttl=51 time=62.0 ms
64 bytes from 213.186.33.13: icmp_req=2 ttl=51 time=64.1 ms

Hey that’s working fine !

Scripting for startup ?¶

On Debian GNU/Linux that’s pretty easy, just copy this script to /usr/local/sbin/source_routing:

#!/bin/sh

# Inserting routes in the adsl1 table
/sbin/ip route add 192.168.1.0/24 dev eth0 scope link table adsl1
/sbin/ip route add default via 192.168.1.1 dev eth0 table adsl1

# Inserting routes in the adsl2 table
/sbin/ip route add 192.168.2.0/24 dev eth0 scope link table adsl2
/sbin/ip route add default via 192.168.1.1 dev eth0 table adsl1

# ip rule is the source routing magic. This will redirect
# packets coming from source "X" to table "adsl1", "adsl2" or "default".
/sbin/ip rule add from 192.168.1.0/24 table adsl1
/sbin/ip rule add from 192.168.2.0/24 table adsl2

Verify permissions: chmod +x /usr/local/sbin/source_routing

You can use post-up scripts of /etc/network/interfaces to run this script.

/etc/network/interfaces

auto eth0
iface eth0 inet static
    address 192.168.0.1
    netmask 255.255.255.0
    post-up /usr/local/sbin/source_routing

auto eth0:adsl1
iface eth0:adsl1 inet static
    address 192.168.1.2
    netmask 255.255.255.0
    gateway 192.168.1.1

auto eth0:adsl2
iface eth0:adsl2 inet static
    address 192.168.2.2
    netmask 255.255.255.0

Don’t forget to execute the script once by hand or thru service networking restart.

Configuring MLVPN¶

MLVPN have two configuration files on each side.

Client side¶

mlvpn0.conf¶

I’ve made the configuration file as small as possible to have a good overview.

Take a look at example config files for more details. (man mlvpn.conf can be usefull)

/etc/mlvpn/mlvpn0.conf

[general]
statuscommand = "/etc/mlvpn/mlvpn0_updown.sh"
tuntap = "tun"
loglevel = 4
mode = "client"
protocol = "udp"
interface_name = "mlvpn0"
timeout = 30

[adsl1]
bindhost = "192.168.1.2"
remotehost = "128.128.128.128"
remoteport = 5080
bandwidth_upload = 61440
bandwidth_download = 512000
latency_increase = 10

[adsl2]
bindhost = "192.168.2.2"
remotehost = "128.128.128.128"
remoteport = 5081
bandwidth_upload = 61440
bandwidth_download = 512000

Little note, we are adding 10 ms of latency on adsl1 to match the latency of adsl2. This is a little trick to help mlvpn aggregation. (Latency must be matched)

mlvpn0_updown.sh¶

This file MUST be chmod 700 (rwx——) owned by root.

chmod 700 /etc/mlvpn/mlvpn0_updown.sh; chown root:root /etc/mlvpn/mlvpn0_updown.sh

Again I stripped the script to the minimum.

/etc/mlvpn/mlvpn0_updown.sh

#!/bin/bash

error=0; trap "error=$((error|1))" ERR

tuntap_intf="$1"
newstatus="$2"
rtun="$3"

[ -z "$newstatus" ] && exit 1

(
if [ "$newstatus" = "tuntap_up" ]; then
    echo "$tuntap_intf setup"
    /sbin/ifconfig $tuntap_intf 10.42.42.2 netmask 255.255.255.252 mtu 1400 up
    route add proof.ovh.net gw 10.42.42.2
elif [ "$newstatus" = "tuntap_down" ]; then
    echo "$tuntap_intf shutdown"
    route del proof.ovh.net gw 10.42.42.2
    /sbin/ifconfig $tuntap_intf down
elif [ "$newstatus" = "rtun_up" ]; then
    echo "rtun [${rtun}] is up"
elif [ "$newstatus" = "rtun_down" ]; then
    echo "rtun [${rtun}] is down"
fi
) >> /var/log/mlvpn_commands.log 2>&1

exit $errors

Again ensure permissions are correct or mlvpn will NOT execute the script.

Server side¶

mlvpn0.conf¶

[general]
statuscommand = "/etc/mlvpn/mlvpn0_updown.sh"
tuntap = "tun"
loglevel = 4
mode = "server"
protocol = "udp"
interface_name = "mlvpn0"
timeout = 30

[adsl1]
bindport = 5080
bandwidth_upload = 61440
bandwidth_download = 512000
latency_increase = 10

[adsl2]
bindport = 5081
bandwidth_upload = 61440
bandwidth_download = 512000

mlvpn0_updown.sh¶

#!/bin/bash

error=0; trap "error=$((error|1))" ERR
tuntap_intf="$1"
newstatus="$2"
rtun="$3"
[ -z "$newstatus" ] && exit 1
(
if [ "$newstatus" = "tuntap_up" ]; then
    echo "$tuntap_intf setup"
    /sbin/ifconfig $tuntap_intf 10.42.42.1 netmask 255.255.255.252 mtu 1400 up
    # NAT thru our server (eth0 is our output interface on the server)
    # mlvpn0 link
    /sbin/iptables -t nat -A POSTROUTING -o eth0 -s 10.42.42.0/30 -j MASQUERADE
    # LAN 192.168.0.0/24 from "client"
    /sbin/route add -net 192.168.0.0/24 gw 10.42.42.2
    /sbin/iptables -t nat -A POSTROUTING -o eth0 -s 192.168.0.0/24 -j MASQUERADE
elif [ "$newstatus" = "tuntap_down" ]; then
    /sbin/route add -net 192.168.0.0/24 gw 10.42.42.2
    /sbin/iptables -t nat -D POSTROUTING -o eth0 -s 10.42.42.0/30 -j MASQUERADE
    /sbin/iptables -t nat -D POSTROUTING -o eth0 -s 192.168.0.0/24 -j MASQUERADE
fi
) >> /var/log/mlvpn_commands.log 2>&1
exit $errors

Testing¶

Double check permissions of /etc/mlvpn/*.sh (chmod 700 owned by root)

Don’t forget to accept UDP 5080 and 5081 on your firewall, server side.

root@server:~ # iptables -I INPUT -i eth0 -p udp --dport 5080 -s [ADSL1_PUBLICIP] -j ACCEPT
root@server:~ # iptables -I INPUT -i eth0 -p udp --dport 5081 -s [ADSL2_PUBLICIP] -j ACCEPT

Start mlvpn on server side manually

root@server:~ # mlvpn --user mlvpn -c /etc/mlvpn/mlvpn0.conf

Start mlvpn on client side manually

root@client:~ # mlvpn --user mlvpn -c /etc/mlvpn/mlvpn0.conf

Check logfiles on client

root@client:~ # cat /var/log/mlvpn_commands.log
mlvpn0 setup
rtun [adsl1] is up
rtun [adsl2] is up

Seems good. Some test ping

# Testing connectivity to the server (tunnel address space)
root@client:~ # ping -n -c2 -I10.42.42.2 10.42.42.1
# Testing connectivity to the server (LAN address space)
root@client:~ # ping -n -c1 -I192.168.0.1 10.42.42.1
# Testing connectivity to the internet
root@client:~ # ping -n -c1 -I192.168.0.1 proof.ovh.net
# Download speed testing
root@client:~ # wget -O/dev/null http://proof.ovh.net/files/10Gio.dat

Table Of Contents

  • Configuring Linux routing for use with multi link MLVPN
    • Introduction
    • Example case
    • Testing the basic configuration
    • Configuring the source routing
      • Concepts
      • Let’s configure it
      • Testing
      • Scripting for startup ?
    • Configuring MLVPN
      • Client side
        • mlvpn0.conf
        • mlvpn0_updown.sh
      • Server side
        • mlvpn0.conf
        • mlvpn0_updown.sh
    • Testing

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