Can’t connect to other machines on remote LAN via OpenVPN after dist-upgrade to Debian Jessie

After I dist-upgraded my Debian Squeeze to Jessie, I couldn’t connect to any machine on the remote LAN anymore after connecting via OpenVPN. The VPN connection to the OpenVPN server on my Debian server was successful, but I couldn’t ping or access machines on the remote network.

I found the solution to my problem by chance while searching for another error I found in the OpenVPN server logfile:

Fri Jan 22 16:20:40 2016 us=402991 pc/84.136.146.84:60860 MULTI: bad source address from client [fe80::487c:a5ff:f332:3df7], packet dropped
Fri Jan 22 16:20:44 2016 us=603301 pc/84.136.146.84:60860 UDPv4 WRITE [53] to [AF_INET]84.136.146.84:60860: P_DATA_V1 kid=0 DATA len=52

While routinely checking the OpenVPN server configuration I noticed, that IP forwarding had been turned off. I don’t know how or why this happened during apt-get dist-upgrade, but after re-enabling it, I was able to connect to the remote machines instantly:

cat /proc/sys/net/ipv4/ip_forward
# 0
echo 1 > /proc/sys/net/ipv4/ip_forward
cat /proc/sys/net/ipv4/ip_forward
# 1

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Über Stefan

Polyglot Clean Code Developer

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