How to configure Ubuntu as router in Vagrant

user_5254851 0
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I'm trying to configure a simple network structure using Vagrant as depicted in the following figure:

enter image description here

As you can see I aim to simulate a hacker attack which goes from attacker through router and reaches victim, but that's not important for the problem I'm struggling with.

This is my Vagrantfile so far (VritualBox is used as provider):

Vagrant.configure("2") do |config|

  config.vm.define "router" do |router|
    router.vm.box = "hashicorp/bionic64"

    router.vm.network "private_network", ip: "192.168.232.1"
    router.vm.network "private_network", ip: "192.168.248.1"

    router.vm.provision "shell", inline: <<-SHELL
      sudo apt-get install traceroute
      echo -e "\nnet.ipv4.ip_forward=1" >> /etc/sysctl.conf
    SHELL
    router.vm.provision :reload
  end

  config.vm.define "attacker" do |attacker|
    attacker.vm.box = "hashicorp/bionic64"

    attacker.vm.network "private_network", ip: "192.168.232.2"

    attacker.vm.provision "shell",
      inline: "sudo apt-get install traceroute"
    attacker.vm.provision "shell",
      run: "always",
      inline: "sudo route add default gw 192.168.232.1"
  end

  config.vm.define "victim" do |victim|
    victim.vm.box = "hashicorp/bionic64"

    victim.vm.network "private_network", ip: "192.168.248.2"

    victim.vm.provision "shell",
      inline: "sudo apt-get install traceroute"
    victim.vm.provision "shell",
      run: "always",
      inline: "sudo route add default gw 192.168.248.1"
  end

end

Please note that I am using the vagrant-reload plugin so you have to install it before doing vagrant up

vagrant plugin install vagrant-reload

What the Vagrantfile does:

  • set the net.ipv4.ip_forward to 1 in router machine
  • add default gateway 192.168.232.1 to attacker machine
  • add default gateway 192.168.248.1 to victim machine

Just to confirm that enabling net.ipv4.ip_forward worked on router:

$ cat /proc/sys/net/ipv4/ip_forward
1

Unfortunately, I can't get it to work. When I try to ping 192.168.248.2 from the attacker machine then I get no response. Output from traceroute seems to be going through the router machine but it stucks there and never reaches victim:

traceroute to 192.168.248.2 (192.168.248.2), 30 hops max, 60 byte packets
 1  legion (192.168.232.1)  0.300 ms  0.454 ms  0.439 ms
 2  * * *
 3  * * *
 4  * * *
 5  * * *
 6  * * *
 7  * * *

Output from netstat -r on attacker machine:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
default         legion          0.0.0.0         UG        0 0          0 eth1
default         _gateway        0.0.0.0         UG        0 0          0 eth0
10.0.2.0        0.0.0.0         255.255.255.0   U         0 0          0 eth0
_gateway        0.0.0.0         255.255.255.255 UH        0 0          0 eth0
192.168.232.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1

I don't know why the new gateway I have added is named legion but I assume it's somehow taken from my laptop hostname (it's Lenovo Legion named as legion).

Output from netstat -r on victim machine:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
default         legion          0.0.0.0         UG        0 0          0 eth1
default         _gateway        0.0.0.0         UG        0 0          0 eth0
10.0.2.0        0.0.0.0         255.255.255.0   U         0 0          0 eth0
_gateway        0.0.0.0         255.255.255.255 UH        0 0          0 eth0
192.168.248.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1

Output from netstat -r on router machine:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
default         _gateway        0.0.0.0         UG        0 0          0 eth0
10.0.2.0        0.0.0.0         255.255.255.0   U         0 0          0 eth0
_gateway        0.0.0.0         255.255.255.255 UH        0 0          0 eth0
192.168.232.0   0.0.0.0         255.255.255.0   U         0 0          0 eth1
192.168.248.0   0.0.0.0         255.255.255.0   U         0 0          0 eth2

Output from ifconfig on attacker machine:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.2.15  netmask 255.255.255.0  broadcast 10.0.2.255
        inet6 fe80::a00:27ff:febb:1475  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:bb:14:75  txqueuelen 1000  (Ethernet)
        RX packets 1271  bytes 129981 (129.9 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 926  bytes 141073 (141.0 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.232.2  netmask 255.255.255.0  broadcast 192.168.232.255
        inet6 fe80::a00:27ff:fe5f:4829  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:5f:48:29  txqueuelen 1000  (Ethernet)
        RX packets 20  bytes 1704 (1.7 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 137  bytes 10188 (10.1 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 16  bytes 1628 (1.6 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 16  bytes 1628 (1.6 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Output from ifconfig on victim machine:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.2.15  netmask 255.255.255.0  broadcast 10.0.2.255
        inet6 fe80::a00:27ff:febb:1475  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:bb:14:75  txqueuelen 1000  (Ethernet)
        RX packets 973  bytes 101812 (101.8 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 725  bytes 111966 (111.9 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.248.2  netmask 255.255.255.0  broadcast 192.168.248.255
        inet6 fe80::a00:27ff:fe98:9693  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:98:96:93  txqueuelen 1000  (Ethernet)
        RX packets 6  bytes 486 (486.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 38  bytes 2812 (2.8 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 44  bytes 3574 (3.5 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 44  bytes 3574 (3.5 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Output from ifconfig on router machine:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.0.2.15  netmask 255.255.255.0  broadcast 10.0.2.255
        inet6 fe80::a00:27ff:febb:1475  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:bb:14:75  txqueuelen 1000  (Ethernet)
        RX packets 1866  bytes 164707 (164.7 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1301  bytes 165459 (165.4 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.232.1  netmask 255.255.255.0  broadcast 192.168.232.255
        inet6 fe80::a00:27ff:fe90:2720  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:90:27:20  txqueuelen 1000  (Ethernet)
        RX packets 1  bytes 60 (60.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 34  bytes 2466 (2.4 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

eth2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.248.1  netmask 255.255.255.0  broadcast 192.168.248.255
        inet6 fe80::a00:27ff:fe3b:238b  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:3b:23:8b  txqueuelen 1000  (Ethernet)
        RX packets 2  bytes 120 (120.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 34  bytes 2466 (2.4 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 10  bytes 714 (714.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 10  bytes 714 (714.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Do you have any ideas on what could be wrong here? Maybe I'm missing something obvious.

vagrant router ubuntu ip networking
2 Answers

You've got a redundant default gateway on victim and attacker called _gateway. You should delete it and leave only the one going to the router via eth1 interface.

user_131592580

While the answer from @thejazzroot clearly pointed the root cause of my problem, it was not everything I had to do to make it work. For some reason, I was unable to ping victim from attacker (and the other way round) until I pinged one of those machines from router.

That was strange. Why would the network start working only after machines pinged each other? Now I've found an answer: vagrant automatically assigns host machine with the .1 IP in each subnet (so in my case it was 192.168.232.1 and 192.168.248.1). Unluckily, those are exactly the same IPs I assigned to my router VM and which attacker/victim machines have set as their gateways! So there were 2 machines with the very same IPs assigned and it seems that when attacker/victim was pinged from router then it somehow chose router over legion. Now it also makes sense where the legion name came from in the output of netstat -r.

TL;DR
I've changed the router IPs in both subnets because there was a conflict with IPs which vagrant automatically assignes to the host machine:

192.168.232.1 -> 192.168.232.10
192.168.248.1 -> 192.168.248.10

In case someone is looking for the full solution, I'm posting my final Vagrantfile here:

Vagrant.configure("2") do |config|

  config.vm.define "attacker" do |attacker|
    attacker.vm.box = "hashicorp/bionic64"
    
    attacker.vm.network "private_network", ip: "192.168.232.2"
    
    attacker.vm.provision "shell",
      run: "always",
      inline: <<-SHELL
        ip route delete default
        ip route add default via 192.168.232.1
      SHELL
  end

  config.vm.define "victim" do |victim|
    victim.vm.box = "hashicorp/bionic64"
    
    victim.vm.network "private_network", ip: "192.168.248.2"
    
    victim.vm.provision "shell",
      run: "always",
      inline: <<-SHELL
        ip route delete default
        ip route add default via 192.168.248.1
      SHELL
  end

  config.vm.define "router" do |router|
    router.vm.box = "hashicorp/bionic64"
    
    router.vm.network "private_network", ip: "192.168.232.1"
    router.vm.network "private_network", ip: "192.168.248.1"
    
    router.vm.provision "shell",
      inline: <<-SHELL
        echo -e "\nnet.ipv4.ip_forward=1" >> /etc/sysctl.conf
        sysctl -p
      SHELL
  end
end
user_52548510
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