Find the answer to your Linux question:
Results 1 to 2 of 2
Enjoy an ad free experience by logging in. Not a member yet? Register.
  1. #1

    openvpn interface, local routing and linux kernel routing table

    from this article: Tun/Tap interface tutorial \1
    the author created a tun interface
        # openvpn --mktun --dev tun2
        # ip link set tun2 up
        # ip addr add dev tun2
    then he did a ICMP ping to
        # ping
        PING ( 56(84) bytes of data.
        From icmp_seq=2 Destination Host Unreachable
        From icmp_seq=3 Destination Host Unreachable
    and he used tshark or tcpdump to capture packets on interface tun2, and he can capture packets as below:
         0.000000 ->     ICMP Echo (ping) request
         0.999374 ->     ICMP Echo (ping) request
         1.999055 ->     ICMP Echo (ping) request
    I followed the same procedures, but I can't capture packets like he did, and I don't get `Destination Host Unreachable`. I think the problem is due to local routing, in his test, it seems that the system regard `` as the default gateway for subnet, but in my test, it is not the case.

    so how can I get the same result as the author's?

    BTW, on my machine:
            tun2      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
                      inet addr:  P-t-P:  Mask:
                      UP POINTOPOINT NOARP MULTICAST  MTU:1500  Metric:1
                      RX packets:7 errors:0 dropped:0 overruns:0 frame:0
                      TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
                      collisions:0 txqueuelen:100
                      RX bytes:420 (420.0 b)  TX bytes:0 (0.0 b)
        route -n
        Kernel IP routing table
        Destination     Gateway         Genmask         Flags Metric Ref    Use Iface         UG    0      0        0 wlan0   U     0      0        0 tun2   U     2      0        0 wlan0
    I don't understand what is the meaning of `` for gateway, so I did add a route:
        route add -net netmask gw
    and get
            Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
           UG    0      0        0 wlan0
     UG    0      0        0 tun2
     U     0      0        0 tun2
     U     2      0        0 wlan0
    still it doesn't work. I really don't understand why.

  2. #2
    Linux Enthusiast Steven_G's Avatar
    Join Date
    Jun 2012
    Western US
    I haven't gotten as far in to it yet as you have. I've been looking at setting up a Tun/Tap for GNS3 instead of OpenVPN. Here's the one I've been looking at. Maybe it will help you?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts