{Solved] OpenVPN subnet broadcast packets

g.

I have been using OpenVPN successfully for many years with a Linux server (static IP) and Windows "road warriors". I have recently been trying to get a new bit of software to work, but the software is trying to connect via a broadcast packet which the Windows machine sends, but the Linux machine doesn't see.

My current connection is using 192.168.132.8/30 (I understand that 192.168.132.9 is the server, 192.168.132.10 is the client)

Using Wireshark on the Windows client, I can see packets on the VPN interface from 192.168.132.10 to 192.168.132.11 (this seems fair enough for a broadcast address for that link).

Using tcpdump on the Linux server, I cannot see these packets (however I can see unicast packets from 192.168.132.10)

Note that the software itself has picked the IP address 192.168.132.11. There is no way for me to change this.

I would like to know how to get OpenVPN to pass this broadcast packet through to the Linux server?

I am using OpenVPN 2.1.1 on both the Linux box and the Windows PC.

From the Linux server-
# ifconfig tun0
tun0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:192.168.132.1 P-t-P:192.168.132.2 Mask:255.255.255.255

From the Windows client-
Ethernet adapter VPN:
Connection-specific DNS Suffix . : example.com
Link-local IPv6 Address . . . . . : fe80::9dd7:d4c0:246d:d35d%17
IPv4 Address. . . . . . . . . . . : 192.168.132.10
Subnet Mask . . . . . . . . . . . : 255.255.255.252
Default Gateway . . . . . . . . . : 192.168.132.9

**** Server config
port 1194
proto udp
dev tun
ca ca.crt
cert server.crt
dh dh1024.pem
server 192.168.132.0 255.255.255.0
ifconfig-pool-persist ipp.txt
push "route 192.168.0.0 255.255.0.0"
;Comment out if wanting to use VPN only to access secure network
;Leave uncommented if using VPN for all internet access
push "redirect-gateway"
push "dhcp-option DNS 192.168.131.3"
push "dhcp-option DNS 192.168.131.1"
push "dhcp-option WINS 192.168.131.1"
push "dhcp-option DOMAIN example.com"
client-to-client
keepalive 10 120
comp-lzo
user nobody
group nobody
persist-key
persist-tun
status openvpn-status.log
verb 3

****client config
client
dev tun
proto udp
remote vpn.example.com 1194
float
resolv-retry infinite
nobind
persist-key
persist-tun
ca ca.crt
cert pc36.crt
key pc36.key
comp-lzo
verb 3

maikcat

tun interface operates at layer3...

if you want broadcasts to work you will have to switch to bridging mode..

Michael.

g.

maikcat wrotetun interface operates at layer3...

if you want broadcasts to work you will have to switch to bridging mode..

OK, thanks. I was aware of the layer 2/3 differences between the tun and tap interfaces, but thought it would be OK since it was a layer 3 broadcast. Turns out to not be the case.

Thanks for your help.