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Re: [Openvpn-users] No ping to the other side of tunnel


  • Subject: Re: [Openvpn-users] No ping to the other side of tunnel
  • From: Leonard Isham <leonard.isham@xxxxxxxxx>
  • Date: Fri, 23 Sep 2005 08:55:01 -0400

On 9/21/05, Attila Fulop <bata@xxxxxxxx> wrote:
> Thanks Leonard for your reply.
>
> /I forgot to wrote in my prior mail, I also made sure *echo 1 >
> /proc/sys/net/ipv4/ip_forward/
>
> *The client receives IP address 10.8.77.6
>
> The server side:
> tun0      Link encap:Point-to-Point Protocol
>          inet addr:10.8.77.1  P-t-P:10.8.77.2  Mask:255.255.255.255
>
>
> Tracerouting from the server:
> -----------------------------
> mosoly:/home/fulop # traceroute -n 10.8.77.6
> traceroute to 10.8.77.6 (10.8.77.6), 30 hops max, 40 byte packets
>  1  * * *
>  2  * * *
>  3  * * *
>  4  * * *
>  5  * * *
>  6  * * *
>
> Tracerouting from the client:
> -----------------------------
>
> C:\Documents and Settings\fulop.BP>tracert -d -h 4 10.8.77.5
>
> Tracing route to 10.8.77.5 over a maximum of 4 hops
>
>  1    43 ms    58 ms    42 ms  10.8.77.1
>  2     *        *        *     Request timed out.
>  3     *        *        *     Request timed out.
>  4     *        *        *     Request timed out.
>
> Trace complete.
>
>
> C:\Documents and Settings\fulop.BP>tracert -d -h 6 10.8.77.1
>
> Tracing route to 10.8.77.1 over a maximum of 6 hops
>
>  1     *        *        *     Request timed out.
>  2     *        *        *     Request timed out.
>  3     *        *        *     Request timed out.
>  4     *        *        *     Request timed out.
>  5     *        *        *     Request timed out.
>  6     *        *        *     Request timed out.
>
> Trace complete.
>
> I've made two pings on the client (ping 10.8.77.1, ping 10.8.77.5),
> and here's what I got on the server:
> mosoly:/home/fulop # tcpdump -n -i tun0
> tcpdump: listening on tun0
> 15:55:20.227786 10.8.77.6 > 10.8.77.1: icmp: echo request
> 15:55:25.391548 10.8.77.6 > 10.8.77.1: icmp: echo request
> 15:55:29.446354 10.8.77.6 > 10.8.77.5: icmp: echo request
> 15:55:29.446416 10.8.77.6 > 10.8.77.5: icmp: echo request
>
> mosoly:/home/fulop # tcpdump -n -i eth0 udp port 1194
> tcpdump: listening on eth0
> 15:59:05.167704 192.168.77.10.1194 > 62.68.166.251.1862: udp 53 (DF)
> 15:59:09.399931 62.68.166.251.1862 > 192.168.77.10.1194: udp 53
> 15:59:14.596933 62.68.166.251.1862 > 192.168.77.10.1194: udp 101
> 15:59:15.727704 192.168.77.10.1194 > 62.68.166.251.1862: udp 53 (DF)
> 15:59:20.915199 62.68.166.251.1862 > 192.168.77.10.1194: udp 101
> 15:59:25.917726 192.168.77.10.1194 > 62.68.166.251.1862: udp 53 (DF)
>
> 6 packets received by filter
> 0 packets dropped by kernel
>
> Sorry, I don't exactly know how I should tcpdump on the server,
> and what should I watch in order to obtain where the replies are sent.
>
> Best regards
>
> >
> >Packets are unidirectional.  Requests are sent, but replies are not received.
> >
> >Run tcpdump on the destination (10.8.77.1.137) and confirm the packets
> >are received.  Check where the replies are sent to if there are any.
> >
> >Run traceroute/tracert from both systems (10.8.77.6.137 &
> >10.8.77.1.137) to see where the packets route.
> >

Please stop posting it makes it difficult to follow the thread, and
harder to help you.

1. Install winpcap and ethereal on the windows systems.
2. Make sure system times are in sync.
3. start a capture on both systems, and Open VPN Interfaces (Ethernet
and tunnel).

Test and compare the captures.

--
Leonard Isham, CISSP
Ostendo non ostento.

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