Chapter 24. Getting started with Multipath TCP

Procedure

1. Enable MPTCP sockets in the kernel:

   # echo "net.mptcp.enabled=1" > /etc/sysctl.d/90-enable-MPTCP.conf
   # sysctl -p /etc/sysctl.d/90-enable-MPTCP.conf

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2. Optional: The RHEL kernel default for subflow limit is 2. If you require more:

   1. Create the /etc/systemd/system/set_mptcp_limit.service file with the following content:

      [Unit]
      Description=Set MPTCP subflow limit to 3
      After=network.target
      
      [Service]
      ExecStart=ip mptcp limits set subflows 3
      Type=oneshot
      
      [Install]
      WantedBy=multi-user.target

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      The oneshot unit executes the ip mptcp limits set subflows 3 command after your network (network.target) is operational during every boot process.

      The ip mptcp limits set subflows 3 command sets the maximum number of additional subflows for each connection, so 4 in total. It is possible to add maximally 3 additional subflows.

   2. Enable the set_mptcp_limit service:

      # systemctl enable --now set_mptcp_limit

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3. Enable MPTCP on all connection profiles that you want to use for connection aggregation:

   # nmcli connection modify <profile_name> connection.mptcp-flags signal,subflow,also-without-default-route

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   The connection.mptcp-flags parameter configures MPTCP endpoints and the IP address flags. If MPTCP is enabled in a NetworkManager connection profile, the setting will configure the IP addresses of the relevant network interface as MPTCP endpoints.

   By default, NetworkManager does not add MPTCP flags to IP addresses if there is no default gateway. If you want to bypass that check, you need to use the also-without-default-route flag.

Verification

1. Verify that you enabled the MPTCP kernel parameter:

   # sysctl net.mptcp.enabled
   net.mptcp.enabled = 1

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2. Verify that you set the subflow limit correctly, in case the default was not enough:

   # ip mptcp limit show
   add_addr_accepted 2 subflows 3

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3. Verify that you configured the per-address MPTCP setting correctly:

   # ip mptcp endpoint show
   192.0.2.1 id 1 subflow dev enp4s0
   198.51.100.1 id 2 subflow dev enp1s0
   192.0.2.3 id 3 subflow dev enp7s0
   192.0.2.4 id 4 subflow dev enp3s0
   ...

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Procedure

1. Enable mptcp.enabled option in the kernel with the following command:

   # echo "net.mptcp.enabled=1" > /etc/sysctl.d/90-enable-MPTCP.conf
   # sysctl -p /etc/sysctl.d/90-enable-MPTCP.conf

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2. Enable and start the mptcpd service:

   # systemctl enable --now mptcp.service

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3. To configure mptcpd service manually, modify the /etc/mptcpd/mptcpd.conf configuration file.

   Note, that the endpoint, which mptcpd service creates, lasts till the host shutdown.