As of December 6, 2019, Tencent Cloud no longer supports Public Network Gateway configuration when purchasing a CVM. If you need to configure a gateway, following these instructions.

Scenario

If some of your CVMs in Tencent Cloud VPC do not have common public IP addresses but need to access the Internet, you can use a CVM with a public IP (common or elastic public IP) as the public gateway to enable them to access the Internet. The public gateway CVM translates the source IP of outbound traffic. When any other CVMs access the Internet through the public gateway CVM, the public gateway CVM translates their IPs to the public IP of the public gateway CVM, as shown in the figure below.

Prerequisites

• Log in to the CVM Console.
• The public gateway CVM and the CVMs that need to access the Internet through the public gateway CVM are located in different subnets because the public gateway CVM can only forward routing requests from other subnets.
• The public gateway CVM must be a Linux CVM. A Windows CVM cannot serve as a public gateway.

Directions

Step 1: Bind an elastic public IP (optional)

If the CVM that serves as the public gateway already has a public IP address, skip this step.

1. In the navigation panel to the left, click EIP to go to the EIP management page.
2. Find the target elastic public IP and select More > Bind in the Operation column to bring up the Bind resources window.
   
3. Select a CVM instance to serve as the public gateway and bind it to the elastic public IP.
   

Step 2: Configure a routing table for the subnet of the gateway

The gateway subnet and other subnets cannot use the same route table. A separate route table must be created for the gateway subnet.

1. Create a custom route table
2. Associate the route table with the subnet where the public gateway CVM is located as prompted.
   

Step 3: Configure a route table for the other subnets

This route table directs all traffic from the CVMs without a public IP to the gateway so they can access public networks as well.
In the route table for the common subnet, add the following routing policy:

• Destination: public IP to be accessed.
• Next-hop type: CVM.
• Next hop: private IP of the CVM instance to which the elastic public IP is bound in Step 1.
  

Step 4: Configure the public gateway

1. Log in to the public gateway CVM, enable network forwarding and NAT proxy, and optimize related parameters.

   1. Run the following command to create a file named vpcGateway.sh in usr/local/sbin.

      vim /usr/local/sbin/vpcGateway.sh

   2. Press i to enter edit mode and add the following code in the script:

      #!/bin/bash
      echo "----------------------------------------------------"
      echo "          `date`"
      
      echo "(1)ip_forward config......"
      file="/etc/sysctl.conf"
      grep -i "^net\.ipv4\.ip_forward.*" $file &>/dev/null && sed -i \
      's/net\.ipv4\.ip_forward.*/net\.ipv4\.ip_forward = 1/' $file || \
      echo "net.ipv4.ip_forward = 1"  >> $file
      echo 1 >/proc/sys/net/ipv4/ip_forward 
      [ `cat /proc/sys/net/ipv4/ip_forward` -eq 1 ] && echo "-->ip_forward:Success" || \
      echo "-->ip_forward:Fail"
      
      echo "(2)Iptables set......"
      iptables -t nat -A POSTROUTING -j MASQUERADE && echo "-->nat:Success" || echo "-->nat:Fail"
      iptables -t mangle -A POSTROUTING -p tcp -j TCPOPTSTRIP --strip-options timestamp && \
      echo "-->mangle:Success" || echo "-->mangle:Fail"
      
      echo "(3)nf_conntrack config......"
      echo 262144 >  /sys/module/nf_conntrack/parameters/hashsize
      [ `cat /sys/module/nf_conntrack/parameters/hashsize` -eq 262144 ] && \
      echo "-->hashsize:Success" ||  echo "-->hashsize:Fail"
      
      echo 1048576 > /proc/sys/net/netfilter/nf_conntrack_max
      [ `cat /proc/sys/net/netfilter/nf_conntrack_max` -eq 1048576 ] && \
      echo  "-->nf_conntrack_max:Success" ||  echo  "-->nf_conntrack_max:Fail"
      
      echo 10800 >/proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established \
      [ `cat /proc/sys/net/netfilter/nf_conntrack_tcp_timeout_established` -eq 10800 ] \
      && echo  "-->nf_conntrack_tcp_timeout_established:Success" ||  \
      echo  "-->nf_conntrack_tcp_timeout_established:Fail"

   3. Press Esc to exit edit mode and enter :wq to save the file and go back. Then, run the following commands:

        chmod +x /usr/local/sbin/vpcGateway.sh
        echo "/usr/local/sbin/vpcGateway.sh  >/tmp/vpcGateway.log 2>&1" >> /etc/rc.local

2. Set the RPS of the public gateway.

   1. Run the following command to create a file named setrps.sh in usr/local/sbin.

      vim /usr/local/sbin/set_rps.sh

   2. Press i to enter edit mode and add the following code in the script:

      #!/bin/bash
      echo "--------------------------------------------"
      * date
      mask=0
      i=0
      total_nic_queues=0
      
      get_all_mask() {
            local cpu_nums=$1
            if [ $cpu_nums -gt 32 ]; then
                    mask_tail=""
                    mask_low32="ffffffff"
                    idx=$((cpu_nums / 32))
                    cpu_reset=$((cpu_nums - idx * 32))
      
                    if [ $cpu_reset -eq 0 ]; then
                            mask=$mask_low32
                            for ((i = 2; i <= idx; i++)); do
                                    mask="$mask,$mask_low32"
                            done
                    else
                        for ((i = 1; i <= idx; i++)); do
                            mask_tail="$mask_tail,$mask_low32"
                    done
                    mask_head_num=$((2 ** cpu_reset - 1))
                    mask=$(printf "%x%s" $mask_head_num $mask_tail)
                fi
            else
                mask_num=$((2 ** cpu_nums - 1))
                mask=$(printf "%x" $mask_num)
            fi
            echo $mask
      }
      set_rps() {
          if ! command -v ethtool &>/dev/null; then
            source /etc/profile
          fi
      
          ethtool=$(which ethtool)
      
          cpu_nums=$(cat /proc/cpuinfo | grep processor | wc -l)
          if [ $cpu_nums -eq 0 ]; then
              exit 0
          fi
      
          mask=$(get_all_mask $cpu_nums)
          echo "cpu number:$cpu_nums  mask:0x$mask"
      
          ethSet=$(ls -d /sys/class/net/eth*)
      
          for entry in $ethSet; do
              eth=$(basename $entry)
              nic_queues=$(ls -l /sys/class/net/$eth/queues/ | grep rx- | wc -l)
              if (($nic_queues == 0)); then
                  continue
              fi
      
              cat /proc/interrupts | grep "LiquidIO.*rxtx" &>/dev/null
              if [ $? -ne 0 ]; then # not smartnic
                  #multi queue don't set rps
                  max_combined=$(
                      $ethtool -l $eth 2>/dev/null | grep -i "combined" | head -n 1 | awk '{print $2}'
                  )
                  #if ethtool -l $eth goes wrong.
                  [[ ! "$max_combined" =~ ^[0-9]+$ ]] && max_combined=1
                  if [ ${max_combined} -ge ${cpu_nums} ]; then
                      echo "$eth has equally nic queue as cpu, don't set rps for it..."
                      continue
                  fi
              else
                 echo "$eth is smartnic, set rps for it..."
              fi
      
              echo "eth:$eth  queues:$nic_queues"
              total_nic_queues=$(($total_nic_queues + $nic_queues))
              i=0
              while (($i < $nic_queues)); do
                  echo $mask >/sys/class/net/$eth/queues/rx-$i/rps_cpus
                  echo 4096 >/sys/class/net/$eth/queues/rx-$i/rps_flow_cnt
                    i=$(($i + 1))
             done
          done
      
          flow_entries=$((total_nic_queues * 4096))
          echo "total_nic_queues:$total_nic_queues  flow_entries:$flow_entries"
          echo $flow_entries >/proc/sys/net/core/rps_sock_flow_entries
      }
      set_rps

   3. Press Esc to exit edit mode and enter :wq to save the file and go back. Then, run the following commands:

      chmod +x /usr/local/sbin/set_rps.sh
      echo "/usr/local/sbin/set_rps.sh >/tmp/setRps.log 2>&1" >> /etc/rc.local

3. Reboot the gateway CVM to apply the configurations. Then, test if a CVM that has no public IP can access the Internet through the public gateway CVM.