Strange result as DHCP client after connected to VPN

weilun.huang@outlook.com

I'm evaluating OpenVPN before buying a license.
I've setup OpenVPN Access Server and in Admin Web UI I set:

    Dynamic IP Address Network: 192.168.100.0/24
    Static IP Address Network:192.168.10.0/24
    Should VPN clients have access to private subnets: Yes, using NAT
    Should client Internet traffic be routed throught the VPN: Yes
    Have clients use the same DNS server as the Access Server host

However, after connected to VPN with a Windows 7 client download from Web Client UI, network configuration is different from what I expected. I was expecting to see subnet mask length equals 24 but it resulted in 25 and for some reason, default gateway is missing thus my client does not have any access outside the subnet nor the internet.

Ethernet adapter Local Area Connection 2:
   Connection-specific DNS Suffix  . : lab.honeywell.com
   Description . . . . . . . . . . . : TAP Adapter OAS NDIS 6.0
   Physical Address. . . . . . . . . : 00-FF-46-B6-73-00
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   Link-local IPv6 Address . . . . . : fe80::b4cd:8620:f44f:3b51%37(Preferred)
   IPv4 Address. . . . . . . . . . . : 192.168.100.133(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.128
   Lease Obtained. . . . . . . . . . : Thursday, April 14, 2016 3:01:53 PM
   Lease Expires . . . . . . . . . . : Friday, April 14, 2017 3:01:53 PM
   Default Gateway . . . . . . . . . :
   DHCP Server . . . . . . . . . . . : 192.168.100.129
   DHCPv6 IAID . . . . . . . . . . . : 620822342
   DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-1E-0C-BB-DC-34-E6-D7-86-99-6E
   DNS Servers . . . . . . . . . . . : 10.202.72.116
                                       10.202.72.118
   NetBIOS over Tcpip. . . . . . . . : Enabled

I've setup OpenVPN Access Server on Ubuntu 14.04 with installation package

openvpn-as-2.0.25-Ubuntu14.amd_64.deb

On my Access Server host there are two NICs, one to the internet and the other connects to the 10.202.72.0/24 subnet where DNS servers should be routed to. Route table should be fine as internet access is good on Access Server host.

The Johan

The network configuration looks fine. I assume 192.168.100.0/24 is the subnet configured as the VPN subnet, and I assume that that subnet is unique and not in use elsewhere in your network. The reason the subnet is split up is because OpenVPN at the moment is single-thread and to make use of both TCP and UDP connections and to make use of multiple processors, there will be multiple OpenVPN daemons, and each will have their share of the subnet. No worries, they can all connect to each other just fine.

There is no default gateway defined on the virtual network adapter, because a system can have only one default gateway. That is why it is called the default gateway. Routing to the target subnet(s) is handled in the routing table. There should be two routes present that override the default gateway. 0.0.0.0/1 and 128.0.0.0/1. You can verify this by looking at the route table on your client computer or by using traceroute to trace the route of some test ping packets. It should go through the VPN server first.