Overview

If you select a bandwidth with an upper limit of 0 Mbps when purchasing a CVM, the CVM will be unable to access the public network. This document uses CentOS 7.5 as an example to describe how a CVM without a public IP address can access the public network by connecting to a CVM with a public IP address through a PPTP VPN.

Prerequisites

• Two CVMs in the same VPC instance have been created. One CVM does not have a public IP address and the other CVM has a public IP address.
• The private IP address of the CVM with a public IP address has been obtained.

Directions

Configuring PPTP on the CVM with a public IP address

1. Log in to the CVM with a public IP address.
2. Run the following command to install PPTP:

   yum install -y pptpd

3. Run the following command to open the pptpd.conf configuration file:

   vim /etc/pptpd.conf

4. Press i to switch to the editing mode and add the following code at the bottom of the file.

   localip 192.168.0.1
   remoteip 192.168.0.234-238,192.168.0.245

5. Press Esc, enter :wq, and save and close the file.
6. Run the following command to open the /etc/ppp/chap-secrets configuration file:

   vim /etc/ppp/chap-secrets

7. Press i to switch to the editing mode and add the username and password for connecting to PPTP in the following format at the bottom of the file.

   <Username>    pptpd    <Password>    *

   For example, if the username and password for connecting to PPTP are root and 123456 respectively, add the following code:

   root    pptpd    123456    *

8. Press Esc, enter :wq, and save and close the file.
9. Run the following command to start the PPTP service:

   systemctl start pptpd

10. Run the following commands sequentially to enable forwarding:

    echo 1 > /proc/sys/net/ipv4/ip_forward
    iptables -t nat -A POSTROUTING -o eth0 -s 192.168.0.0/24 -j MASQUERADE

Configuring PPTP on the CVM without a public IP address

1. Log in to the CVM without a public IP address.
2. Run the following command to install a PPTP client:

   yum install -y pptp pptp-setup

3. Run the following command to create a configuration file:

   pptpsetup --create <Configuration file name> --server <Private IP address of the CVM with a public IP address> --username <Username for connecting to PPTP> --password <Password for connecting to PPTP> --encrypt

   For example, if you have obtained the private IP address 10.100.100.1 of the CVM with a public IP address, run the following command to create a test configuration file:

   pptpsetup --create test --server 10.100.100.1 --username root --password 123456 --encrypt

4. Run the following command to connect to PPTP:

   pppd call test (the configuration file name created in step 3)

5. Run the following commands to set routes:

   route add -net 10.0.0.0/8 dev eth0
   route add -net 172.16.0.0/12 dev eth0
   route add -net 192.168.0.0/16 dev eth0
   route add -net 169.254.0.0/16 dev eth0
   route add -net 9.0.0.0/8 dev eth0
   route add -net 100.64.0.0/10 dev eth0
   route add -net 0.0.0.0 dev ppp0

Checking whether the configuration was successful

Run the following command on the CVM without a public IP address to ping any external network address and check whether it can be pinged through:

ping -c 4 <External network address>

If a result similar to the following is returned, the configuration was successful: