Help & DocumentationVirtual Private CloudBest PractiseAllow VPC CVMs without Public IPs to Access Internet via Public Network Gateway

Allow VPC CVMs without Public IPs to Access Internet via Public Network Gateway

Last updated: 2018-10-18 15:57:12


1. Environment Description

If you need to access the public network but the CVM on the Tencent Cloud VPC has no public IP, you can purchase a CVM with public network gateway as the public network egress during access to the Internet for the CVM without public IP. The public network gateway CVM will carry out source address translation for outbound traffic, and the source IP of traffic by all other CVMs accessing the public network is converted to the IP address of public network gateway CVM after passing through the public network gateway, as shown below:

Ordinary CVM has no public IP, but it can use the public network gateway to access the Internet.

Please perform several steps below to complete the above architecture.

2. Architecture Building

2.1. Creating a Gateway Subnet

The public network gateway can only forward the route forwarding request of the subnet to which it does not belong, so the public network gateway cannot be in the same subnet with the CVM which needs to access the public network through the public network gateway. Therefore, it is necessary to set up a separate gateway subnet first.

2.2. Purchasing a Public Network Gateway

To purchase the public network gateway in the gateway subnet created above, please refer to Purchasing a VPC Public Network Gateway

2.3. Creating the Routing Table of Gateway Subnet

Gateway subnet and ordinary subnet cannot be associated with the same routing table. You need to create a separate gateway routing table and associate it with the gateway subnet.

2.4. Configuring the Routing Table of Ordinary Subnet

Configure the routing table of the ordinary subnet, direct the default route to the public network gateway CVM, so that the CVM in ordinary subnet can access the public network through the route forwarding capability of public network gateway.

3. Configuration Optimization

Public network gateway CVM will set the nat rules of iptables by default, and open the kernel ip_forward. By then, all the basic functions public network gateway have been enabled. It is recommended to perform the following configuration to achieve better performance.

1) Write the net.ipv4.ip_forward configuration to the /etc/sysctl.conf file with the following command

echo "net.ipv4.ip_forward = 1" >> /etc/sysctl.conf

2) Increase the nf_conntrack configuration parameter using the following command

echo "echo 1048576 > /proc/sys/net/netfilter/nf_conntrack_max" >> /etc/rc.local
echo "echo 262144 > /sys/module/nf_conntrack/parameters/hashsize" >> /etc/rc.local

3) Set the forwarding nat rules

echo "iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE" >> /etc/rc.local

4) Turn off the timestamp option

echo "iptables -t mangle -A POSTROUTING -p tcp -j TCPOPTSTRIP --strip-options timestamp" >> /etc/rc.local

5) Set the rps of public network gateway

Create a new script in the directory of /usr/local/sbin/ and write the following code into the script:

cpu_nums=`cat /proc/cpuinfo |grep processor |wc -l`
    exit 0

nic_queues=`cat /proc/interrupts |grep -i virtio0-input |wc -l`
    exit 0

echo "cpu number" $cpu_nums "nic queues" $nic_queues

mask=$(echo "obase=16;2^$cpu_nums - 1" |bc)
flow_entries=$(echo "$nic_queues * 4096" |bc)

echo "mask = "$mask
echo "flow_entries = "$flow_entries

#for i in {0..$nic_queues}
while (($i < $nic_queues))  
    echo $mask > /sys/class/net/eth0/queues/rx-$i/rps_cpus
    echo 4096 > /sys/class/net/eth0/queues/rx-$i/rps_flow_cnt

echo $flow_entries > /proc/sys/net/core/rps_sock_flow_entries

Once created, execute the following command:

chmod +x /usr/local/sbin/
echo "/usr/local/sbin/" >> /etc/rc.local

After the above configuration, restart the public network gateway CVM to make the configuration valid, and test whether the submachine without public network IP can access the public network.