When setting up OpenVPN on GCE, many developers encounter connectivity issues where clients can connect but cannot route traffic properly. The root cause typically lies in three areas:

1. GCE's network firewall rules blocking VPN traffic
2. Missing IP forwarding configuration
3. Incorrect NAT/masquerading setup

First, ensure these firewall rules exist in your GCE project:

gcloud compute firewall-rules create allow-openvpn \
--direction=INGRESS \
--priority=1000 \
--network=default \
--action=ALLOW \
--rules=udp:1194 \
--source-ranges=0.0.0.0/0

Also allow forwarded traffic:

gcloud compute firewall-rules create allow-forwarded-vpn-traffic \
--direction=INGRESS \
--priority=1000 \
--network=default \
--action=ALLOW \
--rules=all \
--source-ranges=10.8.0.0/24

On your GCE instance, enable IP forwarding:

echo 1 > /proc/sys/net/ipv4/ip_forward
sysctl -p

Make this persistent by adding to /etc/sysctl.conf:

net.ipv4.ip_forward = 1

Here's a working server.conf template for GCE:

port 1194
proto udp
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh.pem
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist /var/log/openvpn/ipp.txt
push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DNS 8.8.4.4"
client-to-client
keepalive 10 120
cipher AES-256-CBC
persist-key
persist-tun
status /var/log/openvpn/openvpn-status.log
verb 3
explicit-exit-notify 1

Add these iptables rules on your GCE instance:

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
iptables -A FORWARD -i tun0 -o eth0 -j ACCEPT
iptables -A FORWARD -i eth0 -o tun0 -m state --state RELATED,ESTABLISHED -j ACCEPT

Make them persistent:

apt install iptables-persistent
netfilter-persistent save

If issues persist:

• Check OpenVPN logs: journalctl -u openvpn@server -f
• Verify routing: ip route show
• Test connectivity: tcpdump -i tun0
• Check GCE quotas to ensure you're not hitting limits

When deploying OpenVPN on Google Compute Engine (GCE), the main obstacle isn't the OpenVPN configuration itself - it's GCE's unique networking architecture. Unlike traditional VPS providers, GCE implements additional network abstraction layers that require specific handling.

Here's what you need to verify for a working OpenVPN setup:

# Required GCE firewall rules (run via gcloud CLI)
gcloud compute firewall-rules create allow-openvpn \
    --direction=INGRESS \
    --priority=1000 \
    --network=default \
    --action=ALLOW \
    --rules=udp:1194 \
    --source-ranges=0.0.0.0/0

gcloud compute firewall-rules create allow-openvpn-traffic \
    --direction=INGRESS \
    --priority=1000 \
    --network=default \
    --action=ALLOW \
    --rules=all \
    --source-tags=openvpn

GCE instances don't enable IP forwarding by default. You must configure both the instance and GCE network settings:

# On the GCE instance:
echo 1 > /proc/sys/net/ipv4/ip_forward
sed -i 's/#net.ipv4.ip_forward=1/net.ipv4.ip_forward=1/' /etc/sysctl.conf
sysctl -p

# For persistent forwarding after reboots
echo "net.ipv4.ip_forward = 1" >> /etc/sysctl.conf

Here's a working server configuration template (server.conf) that handles GCE's special requirements:

port 1194
proto udp
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh.pem
server 10.8.0.0 255.255.255.0
push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DNS 8.8.4.4"
keepalive 10 120
cipher AES-256-CBC
user nobody
group nogroup
persist-key
persist-tun
status openvpn-status.log
verb 3
# Critical for GCE
push "route 10.128.0.0 255.128.0.0"

The most common point of failure is proper NAT setup. This iptables configuration works reliably on GCE:

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o ens4 -j MASQUERADE
iptables -A FORWARD -i ens4 -o tun0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i tun0 -o ens4 -j ACCEPT

# Save rules for persistence
apt-get install iptables-persistent -y
netfilter-persistent save

After configuration, test these critical paths:

# On server:
tcpdump -i tun0
ping 10.8.0.1

# On client:
traceroute 8.8.8.8
curl ifconfig.me

If connections work but no internet access, check:

• GCE instance metadata: Enable "IP forwarding" in VM instance settings
• VPC network routes: Should show default internet gateway
• Firewall logs: gcloud compute firewall-rules describe [RULE_NAME]