Routing traffic from Linux through a VirtualBox Windows install

routingvirtualboxvpn

I am trying to connect to an internal client network with my Ubuntu laptop, but the client uses Nortel's Contivity VPN, so it only works in Windows. My idea is to use VirtualBox with Windows XP Guest for establishing the VPN connection, and then using Windows XP as a router to route traffic from my Ubuntu Host via the VPN.

I configured the first adapter in VirtualBox to be a NAT, to make Internet access easy. I configured the 2nd adapter as "Host-only", so I can now see a new vboxnet0 interface on Ubuntu Host, and a 2nd adapter in Windows Guest, which I configured with a static IP.

I've verified that I can ping Ubuntu to Windows and Windows to Ubuntu.

The routing table looks like this:

C:\Documents and Settings\val>route print
===========================================================================
Interface List
0x1 ........................... MS TCP Loopback interface
0x2 ...08 00 27 55 ee 35 ...... AMD PCNET Family PCI Ethernet Adapter #2 - Packet Scheduler Miniport
0x3 ...08 00 27 5f 3e 93 ...... AMD PCNET Family PCI Ethernet Adapter - Packet Scheduler Miniport
0x4 ...44 45 53 54 42 00 ...... Nortel IPSECSHM Adapter - Packet Scheduler Miniport
0x5 ...00 00 00 00 00 01 ...... AGN Virtual Network Adapter - Packet Scheduler Miniport
===========================================================================
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0         10.0.2.2       10.0.2.15       20
         10.0.2.0    255.255.255.0        10.0.2.15       10.0.2.15       20
        10.0.2.15  255.255.255.255        127.0.0.1       127.0.0.1       20
   10.255.255.255  255.255.255.255        10.0.2.15       10.0.2.15       20
        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1
     192.168.56.0    255.255.255.0     192.168.56.2    192.168.56.2       20
     192.168.56.2  255.255.255.255        127.0.0.1       127.0.0.1       20
   192.168.56.255  255.255.255.255     192.168.56.2    192.168.56.2       20
        224.0.0.0        240.0.0.0        10.0.2.15       10.0.2.15       20
        224.0.0.0        240.0.0.0     192.168.56.2    192.168.56.2       20
  255.255.255.255  255.255.255.255        10.0.2.15       10.0.2.15       1
  255.255.255.255  255.255.255.255     192.168.56.2               5       1
  255.255.255.255  255.255.255.255     192.168.56.2               4       1
  255.255.255.255  255.255.255.255     192.168.56.2    192.168.56.2       1
Default Gateway:          10.0.2.2
===========================================================================
Persistent Routes:
  None

192.168.56.2 is the 2nd adapter that is connected to 192.168.56.1 on the Ubuntu Host side.

Now, when I establish the VPN connection, the routing table is changed by Contivity and I can no longer ping the host, and the host can't ping the guest. Here is the routing table with VPN running:

C:\Documents and Settings\val>route print
===========================================================================
Interface List
0x1 ........................... MS TCP Loopback interface
0x2 ...08 00 27 55 ee 35 ...... AMD PCNET Family PCI Ethernet Adapter #2 - Packet Scheduler Miniport
0x3 ...08 00 27 5f 3e 93 ...... AMD PCNET Family PCI Ethernet Adapter - Packet Scheduler Miniport
0x4 ...44 45 53 54 42 00 ...... Nortel IPSECSHM Adapter - Packet Scheduler Miniport
0x5 ...00 00 00 00 00 01 ...... AGN Virtual Network Adapter - Packet Scheduler Miniport
===========================================================================
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0         10.0.2.2       10.0.2.15       21
          0.0.0.0          0.0.0.0    192.168.32.29   192.168.32.29       1
         10.0.2.0    255.255.255.0        10.0.2.15       10.0.2.15       20
         10.0.2.0    255.255.255.0    192.168.32.29   192.168.32.29       1
        10.0.2.15  255.255.255.255        127.0.0.1       127.0.0.1       20
   10.255.255.255  255.255.255.255        10.0.2.15       10.0.2.15       20
        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1
     192.168.32.0    255.255.248.0    192.168.32.29   192.168.32.29       30
    192.168.32.29  255.255.255.255        127.0.0.1       127.0.0.1       30
   192.168.32.255  255.255.255.255    192.168.32.29   192.168.32.29       30
     192.168.56.0    255.255.255.0     192.168.56.2    192.168.56.2       20
     192.168.56.0    255.255.255.0    192.168.32.29   192.168.32.29       1
     192.168.56.2  255.255.255.255        127.0.0.1       127.0.0.1       20
   192.168.56.255  255.255.255.255     192.168.56.2    192.168.56.2       20
   192.197.71.160  255.255.255.255         10.0.2.2       10.0.2.15       1
        224.0.0.0        240.0.0.0        10.0.2.15       10.0.2.15       20
        224.0.0.0        240.0.0.0     192.168.56.2    192.168.56.2       20
        224.0.0.0        240.0.0.0    192.168.32.29   192.168.32.29       1
  255.255.255.255  255.255.255.255        10.0.2.15       10.0.2.15       1
  255.255.255.255  255.255.255.255    192.168.32.29   192.168.32.29       1
  255.255.255.255  255.255.255.255     192.168.56.2               5       1
  255.255.255.255  255.255.255.255     192.168.56.2    192.168.56.2       1
Default Gateway:     192.168.32.29
===========================================================================
Persistent Routes:
  None

By looking at the routing table, I can't see why I'm losing ability to ping 192.168.56.1, so I'd appreciate some help, or ideas on how to further troubleshoot this.

Best Answer

Split tunneling has probably been disabled as part of the VPN policy - standard security practice. You might check with your VPN administrator(s) to see if split tunneling can be allowed for your VPN sessions (you might not want to hold your breathe as slit tunneling is generally consider poor security practice).

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How does my router know whether to send traffic via the internet connection or through the vpn?

With routes; you can do this from pfsense's Static Routes menu.

You need to have a route in place that tells your router where to forward packets to: either a host on the same network or another router that knows where to forward the packets to, and so on, until it reaches it's destination.

However, 171.28.18.50 is not a RFC1918 private address, so unless this is just an example IP for ServerFault, you likely don't have a route for this on either router besides the default route, which would be your next-hop gateway given to you by your ISP.

Linux – How to configure dual homed server in order for both network segments to communicate

There are two problems with this setup:

The hosts on LAN1 know nothing about the LAN2 segment. When you ping a host on LAN1 (let's call it host1) from SRV-02, the packet will be routed through SRV-01 and will reach host1. However, host1 will send the reply to it's default gateway (ISP router) as it doesn't have a specific route to LAN2. (The ISP router will either a) also send it to it's default gateway as it also doesn't know about LAN2, or b) drop the packet as it comes from an unknown source not it's local LAN.)
When trying to reach WAN from LAN2, the packets will be routed through SRV-02 to ISP router where two situations are possible:
- The router will not NAT translate the packet as the source of the packet (LAN2) is not it's local LAN (this is the more probable situation), or
- The router will NAT translate the packet and send it to the Internet. However, when the reply comes and the destination is translated back to the LAN2 address, the packet will not be delivered as the ISP router doesn't have a route for that network. The packet will be sent incorrectly to the default gateway (ISP).

These issues could be fixed by adding a static route to LAN2 to ISP router and adding a source NAT configuration for LAN2 on SRV-01. However, that is not possible due to no admin access to the ISP router.

There are two solutions that get around it:

A. Make SRV-01 a full router for LAN1 and LAN2 hosts

Add another network adapter to SRV-01 (making it 3 in total)
Change the topology as follows:

WAN -> ISP router -> LAN1 -> SRV-01 +-> LAN3 (for hosts originally in LAN1)
                                    +-> LAN2 -> SRV-02

Basically, we're making SRV-01 a router for both LAN segments.

This will require moving hosts originally in LAN1 to a new subnet LAN3 - let's say we use 10.0.1.0/24
The network configuration of SRV-01 will need to be changed as follows:

/etc/network/interfaces:

# LAN1 - to ISP router
auto eth0
iface eth0 inet dhcp
# we can even use dhcp as the IP address is not really important
# - there are no more hosts on LAN1 apart from ISP router and SRV-01

# LAN3 - for hosts originally in LAN1
iface eth1
    address 10.0.1.1
    netmask 255.255.255.0

# LAN2
iface eth2
    address 10.0.2.1
    netmask 255.255.255.0

iptables rules to make WAN access work:

iptables -t nat -A POSTROUTING -o eth0 -s 10.0.1.0/24 -j MASQUERADE
iptables -t nat -A POSTROUTING -o eth0 -s 10.0.2.0/24 -j MASQUERADE

Alternatively, if you choose to keep the static IP address on SRV-01 on eth0 the rules could be changed (although MASQUERADE would still work):

iptables -t nat -A POSTROUTING -o eth0 -s 10.0.1.0/24 -j SNAT --to-source 192.168.5.8
iptables -t nat -A POSTROUTING -o eth0 -s 10.0.2.0/24 -j SNAT --to-source 192.168.5.8

DHCP will need to be configured on SRV-01 on eth1 (LAN3, for hosts originally on LAN1), and possibly on eth2 (LAN2) as well if required. (In both cases the gateway will be the local address of eth1 or eth2 respectively, but that goes without saying :)

This will make communication possible between LAN3 and LAN2 (via SRV-01 which is the default gateway for both). WAN access will also work from both LAN3 and LAN2 thanks to the double source NAT.

B. Make SRV-01 a DHCP server for LAN1

This approach is not as clean as above but is slightly simpler. It assumes you are able to disable DHCP on ISP router

Disable DHCP on ISP router
Set up DHCP for LAN1 on SRV-01 and make SRV-01 (192.168.5.8) the default gateway for LAN1
Set up source NAT translation for LAN2 on SRV-01 so that the WAN access works from LAN2:

iptables -t nat -A POSTROUTING -o eth0 -s 10.0.2.0/24 -d 192.168.5.4 -j SNAT --to-source 192.168.5.8
iptables -t nat -A POSTROUTING -o eth0 -s 10.0.2.0/24 ! -d 192.168.5.0/24 -j SNAT --to-source 192.168.5.8

The first line enables SNAT so that LAN2 hosts can access the ISP router itself and the second line disables SNAT for LAN2-LAN1 access.

Again, this approach is not as clean as the one above as there are two routers in the same subnet (SRV-01, ISP router). When I used this approach myself I noticed my second router (SRV-01 in this scenario) would send ICMP redirects to the ISP router as it would see that the client (host on LAN1) and the upstream router (ISP router) are on the same LAN. This might not be desired as network policies implemented on SRV-01 could be circumvented.

Hope that helps.

Best Answer

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Linux – How to configure dual homed server in order for both network segments to communicate

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