Configuring a Permanent MPTCP Connection

This task shows how to configure a permanent MPTCP connection between two systems.

Before you begin, ensure the following:

Oracle Linux has been configured to enable MPTCP.
Two Oracle Linux systems have more than one interface. For example: eth0 and wlan0.
The names of network interfaces and their assigned IP addresses have been changed to match the environment.
A user with administrator privileges has been configured on both systems. For more information, see Oracle Linux 10: Setting Up System Users and Authentication.

This task uses nmcli to enable MPTCP with subflows across different interfaces (Ethernet and Wi-Fi), between two Oracle Linux 10 systems (referred to as System A and System B).

The following IP ranges are assigned to System A and System B:

System A:

Ethernet: 192.0.2.10/24 (eth0)
Wi-Fi: 198.51.100.10/24 (wlan0)

System B:

Ethernet: 192.0.2.20/24 (eth0)
Wi-Fi: 198.51.100.20/24 (wlan0)

These systems are connected to both networks.

Note:

All steps must be completed on both systems.

To ensure both interfaces are configured and activated, run the following command to verify that the interfaces are present:
```
sudo nmcli connection show
```
If the eth0 and wlan0 connections are missing or down, bring them up with the following commands:
```
sudo nmcli connection up eth0
```
```
sudo nmcli connection up wlan0
```

(Optional) If you're not using DHCP, set static IP addresses for each interface.

For example, on System A, assign static IP addresses as follows:

sudo nmcli connection modify eth0 ipv4.addresses 192.0.2.10/24 ipv4.method manual

sudo nmcli connection modify wlan0 ipv4.addresses 198.51.100.10/24 ipv4.method manual

On System B:

sudo nmcli connection modify eth0 ipv4.addresses 192.0.2.20/24 ipv4.method manual

sudo nmcli connection modify wlan0 ipv4.addresses 198.51.100.20/2 ipv4.method manual

For more information on assigning static IP addresses in Oracle Linux, see Oracle Linux 10: Setting Up Networking With NetworkManager.

Verify the interfaces.
Run ip addr show to confirm that both interfaces are up and have the correct IP addresses:
```
ip addr show eth0
```
```
ip addr show wlan
```
If MPTCP isn't already enabled, enable it:
```
sudo sysctl -w net.mptcp.enabled=1
```
To increase the subflow limits on both systems, configure MPTCP to use both interfaces:
```
sudo ip mptcp limits set subflow 2
```
Test the connectivity between the two systems.
For example, use curl to test that a web page served by System B can be accessed by System A:
```
curl http://192.0.2.20/
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
   <title>Directory listing for /</title>
</head>
<body>
   <h2>Directory listing for /</h2>
   <hr>
...
```
For more information about subflow verification, see the steps described in Testing MPTCP Subflows Using mptcpize.

When you configure network interfaces by using the nmcli command, you can save MPTCP-related system settings in the /etc/sysctl.conf file so that these changes persist between reboots. For more information, see Enabling and Configuring MPTCP.