I encountered this when I was doing my graduation project. The needs at that time were similar to yours:

• FC18 system
• Dual network cards
• One connected to a standard router: ADSL broadband Internet access, fast access to domestic and foreign websites, but cannot access exclusive resources on campus
• One connected to the campus network: access the external network and pop up the Web authentication interface, but you can access exclusive resources within the school without authentication and enjoy LAN speed
• The default behavior of the system at that time seemed to be messed up...

I will share the notes I took at that time.

Beihang Campus Network Features

• The speed is unstable and is obviously affected by the number of users on the campus network.
• Intranet transmission is fast, and the computers in the campus network are all in the same LAN.
• Domestic Internet access speed is average.
• Internet speed abroad is poor.
• Check online that the network segment of Beihang University is: 202.112.128.0/202.122.143.255, and it is confirmed that the financial department, campus network certification, network center and other school organization websites are within this range.

Fedora routing configuration

Because my dormitory computer uses Fedora, I will use Fedora as an example. It's not very clear how to configure it under Windows. First, use dual network cards to connect the campus network port and the router for ADSL broadband at the same time.

Edit the network properties of the adapter p17p1 connected to the Beihang intranet:

• IPv4 Settings: Automatic (DHCP)
• IPv4 Settings-Routing: Address 202.112.128.0 Subnet Mask 255.255.240.0 Gateway 192.168.11.33 Metric
• [V] Ignore automatically acquired routes
• [V] Only use this connection for resources on the corresponding network

For wlan0 connected to the ADSL public network, there is no need to edit the network properties, keep it automatic.

Effect

• Be able to access Beihang campus websites such as the Finance Office and Network Center that cannot be accessed through the public network. At this time, the data goes through the campus network.
• Get stable speeds when accessing any other website. At this time, the data goes through ADSL broadband.

To add, it is not surprising that the IPs of the two network cards are the same, and there is nothing to consider. It is important to investigate the IP or IP segment of the other server of the CMCC business dedicated line. This method only uses the resolved IP address of the other party to determine which network card the data will go to.

route add -net CMCC的网段 netmask xxx dev 第二块网卡的名字

For Python programs, just put socket.connect before socket.bind(('需要用的本地网卡IP', 0)).

This can be done using policy routing under Linux
1. Edit the routing table and add the CMCC dedicated line entry

vim /etc/iproute2/rt_tables
200      cmcc

2. For example, the network card IP of eth2 is 124.0.0.1, and the network segment of the CMCC dedicated line is 124.127.101.0/24. It can be configured as follows

ETH2=eth2
IP2=124.0.0.1
SEGMENT2=124.127.101.0/24

TABLE2=cmcc

ip route add $SEGMENT2 dev $ETH2 src $IP2 table $TABLE2
ip route add default via $IP2 table $TABLE2

ip rule add from $IP2 table $TABLE2