Zero received packet for local bridged network interface

[hk298]

Hi mate,

I am setting up a very simple VPN with one Linux server (Digital Ocean Ubuntu 16.04) and one Window client (Windows 10).
*Ubuntu Linux: version -16.04, network interfaces - eth0 eth1 lo
*Widows 10 Laptop

I installed VPN Server on the Linux and created a local bridge attached to the network interface eth1 (eth1 is for local private network, and eth0 is connecting to the Internet where SoftEther VPN Server is listening on). And I installed VPN Client on the Windows and I assigned static IPs to
*Linux eth1: 192.168.168.80
*Windows vpn virtual network interface: 192.168.168.81

And I tried to have a simple test by pinging the Linux eth1 from the Windows, and it did not work.

To find out the root cause, I ran "tcpdump" on the Linux and the command did show that there was ARP request message arrived:

18:15:01.019824 IP 192.168.168.81.52474 > 239.255.255.250.1900: UDP, length 137
18:15:04.021530 IP 192.168.168.81.52474 > 239.255.255.250.1900: UDP, length 137
18:15:15.190612 ARP, Request who-has 192.168.168.80 tell 192.168.168.81, length 28
18:15:20.270362 IP 192.168.168.81.17500 > 255.255.255.255.17500: UDP, length 133
18:15:20.275895 IP 192.168.168.81.17500 > 255.255.255.255.17500: UDP, length 133
18:15:20.276182 IP 192.168.168.81.17500 > 255.255.255.255.17500: UDP, length 133
18:15:20.276954 IP 192.168.168.81.17500 > 255.255.255.255.17500: UDP, length 133

This indicates the virtual hub and local bridging was somehow working, but there was no ARP reply message. And more interesting the count on received packets on eth1 is always zero:

~$ ifconfig eth1
eth1 Link encap:Ethernet HWaddr 04:01:47:0d:9c:02
inet addr:192.168.168.80 Bcast:192.168.168.255 Mask:255.255.255.0
inet6 addr: fe80::601:47ff:fe0d:9c02/64 Scope:Link
UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:6070 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:1356767 (1.3 MB)

I have verified that there is no rule in iptables setting and the default policy is "accept", and I have disabled ufw firewall. This is really puzzling, it just looks like the packets from virtual bridge is ignored by the network interface completely.

Anyone have some thought, let me know, thanks!

[shobhit]

http://blog.lincoln.hk/blog/2013/05/17/ ... al-bridge/

I created local bridge with the help of above link and it worked for me, at least i can ping bridged adapter through virtual network adapter.

[hk298]

Yes, the instructions in Lincoln's blog works for me too. Thanks very much!

Lincoln's approach is using a virtual/tap network interface for local bridging instead of using one of the existing interfaces. Still don't understand why it doesn't work for physical interface.

[thisjun]

There are some limitation on localbridge on Linux.
http://www.softether.org/4-docs/1-manua ... r_Mac_OS_X