Arch Linux

szczurcio

Member

Registered: 2016-03-31

Posts: 3

Two IP addresses assigned to the same network card - OpenVPN issues?

I have a laptop running Arch Linux. At home, I can connect to my OpenVPN server without problems; however, my college network seems to use some odd configuration where upon connection I'm assigned two IP addresses by DHCP.

ip addr:

    2: wlp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
        link/ether 18:5e:0f:90:55:29 brd ff:ff:ff:ff:ff:ff
        inet xx.xx.127.167/24 brd xx.xx.127.255 scope global wlp3s0
           valid_lft forever preferred_lft forever
        inet xx.xx.127.227/24 brd xx.xx.127.255 scope global secondary wlp3s0
           valid_lft forever preferred_lft forever
        inet6 xx::xx:xx:fe90:5529/64 scope link 
           valid_lft forever preferred_lft forever

I have hidden the addresses because there's no NAT, so those are my actual public IPs.

When I connect to OpenVPN, I'm unable to send any traffic anywhere; even the local IP of the VPN gateway in the LAN, let alone any outside hosts. I suspect the dual IP configuration is responsible for this, because judging from ip route there's no route added for packets originating at that IP:

    0.0.0.0/1 via 10.8.0.5 dev tun0 
    default via xx.xx.127.254 dev wlp3s0  src xx.xx.127.227  metric 302 
    10.8.0.1 via 10.8.0.5 dev tun0 
    10.8.0.5 dev tun0  proto kernel  scope link  src 10.8.0.6 
    <vps ip> via xx.xx.127.254 dev wlp3s0 
    128.0.0.0/1 via 10.8.0.5 dev tun0 
    xx.xx.127.0/24 dev wlp3s0  proto kernel  scope link  src xx.xx.127.227  metric 302 

The default entry restricts the source address to what is listed above as the "secondary address"; I suspect this is what causes the packets not to be sent anywhere. Oddly enough, even if I configure the connection manually, I will still be assigned another, "secondary" IP (I'm using NetworkManager).

I tried addding another route for the .167 address, but to no avail; nothing changes. I should add that the network definitely doesn't block VPN traffic because I can use it on Windows 8 (dual boot on the same laptop) and on my Android phone without problems (same server). Also, there are no warnings or errors displayed during the OpenVPN connection sequence.

Am I correct in my suspicions that this dual IP configuraiton is causing VPN problems?