多网络接口，多ip地址配置路由策略，从那个公网ip进入就从对应的ip出去。

Centos Configuration:

1. Console creates ENI, assigns multiple Private IPs and EIPs

2. Using two network cards as an example

   1. ETH1:
      • EIP: 43.192.X.X, Private IP: 172.31.20.163
      • EIP: 161.189.X.X, Private: 172.31.26.128
   2. ETH0:
      • EIP1: 69.231.X.X, Private IP: 172.31.24.205
      • EIP2: 69.234.X.X, Private IP: 172.31.23.41

3. Create the following files in /etc/sysconfig/network-scripts, each network card and each IP requires a corresponding file:

   ifcfg-eth0 can omit IP and MASK, other configuration files need to write the corresponding Private IP and NET MASK (consistent with subnet configuration)

   ifcfg-eth0:

   
   BOOTPROTO=dhcp
   DEVICE=eth0
   HWADDR=06:aa:d7:88:4d:b2 ##optional
   ONBOOT=yes
   STARTMODE=auto
   TYPE=Ethernet
   USERCTL=no

   ifcfg-eth0:1

   #
   BOOTPROTO=dhcp
   DEVICE=eth0:1
   ONBOOT=yes
   IPADDR=172.31.23.41 # Second IP of ETH0
   NETMASK=255.255.240.0
   STARTMODE=auto
   TYPE=Ethernet
   USERCTL=no

   ifcfg-eth1

   BOOTPROTO=dhcp
   DEVICE=eth1
   ONBOOT=yes
   IPADDR=172.31.20.163 # First IP of ETH1
   NETMASK=255.255.240.0
   STARTMODE=auto
   TYPE=Ethernet
   USERCTL=no

   ifcfg-eth1:1

   BOOTPROTO=dhcp
   DEVICE=eth1:1
   ONBOOT=yes
   IPADDR=172.31.26.128 # Second IP of ETH1
   NETMASK=255.255.240.0
   STARTMODE=auto
   TYPE=Ethernet
   USERCTL=no

4. Update the /etc/rc.local file, adding the following entries to this file to ensure the routing table is automatically updated after the server restarts

   ## Different network cards use different policy routing
   ip route add default via 172.31.16.1 dev eth0 table 1 # ETH0 uses table 1
   ip rule add from 172.31.24.205 lookup 1 # Set source return path 
   ip rule add from 172.31.23.41 lookup 1 
   ip route add default via 172.31.16.1 dev eth1 table 2 # ETH1 uses table 2 
   ip rule add from 172.31.20.163 lookup 2 
   ip rule add from 172.31.26.128 lookup 2 

   After adding, execute chmod +x /etc/rc.d/rc.local

   Restart the system to check if all IPs can communicate properly.

Note: If communication still fails after restarting, configure the rc-local service.

1. Edit /usr/lib/systemd/system/rc-local.service

   Add dependencies:

   In the [Unit] section, ensure the following two lines are included:

   Requires=network-online.target 
   After=network-online.target 

   Save and exit

2. Enable rc-local.service

   sudo systemctl enable rc-local

3. Start the service

   sudo systemctl start rc-local

   sudo systemctl status rc-local

Restart again, and you should be able to ping all IPs.

The configuration for Amazon Linux is simpler since it comes pre-installed with amazon-ec2-net-utils, which automatically recognizes network card information and has fewer configuration items; you can refer to the above steps to update any missing parts accordingly.