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IP-MPTCP

Section: Linux (8)
Updated: 4 Apr 2020
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NAME

i-mptcp - MPTCP path manager configuration

SYNOPSIS

ip [ OPTIONS ] mptcp { endpoint | limits | help }

ip mptcp endpoint add IFADDR [ port PORT ] [ dev IFNAME ] [ id ID ] [ FLA-LIST ]

ip mptcp endpoint delete id ID [ IFADDR ]

ip mptcp endpoint change [ id ID ] [ IFADDR ] [ port PORT ] CHANG-OPT

ip mptcp endpoint show [ id ID ]

ip mptcp endpoint flush

FLA-LIST := [ FLA-LIST ] FLAG

FLAG := [ signal | subflow | backup | fullmesh ]

CHANG-OPT := [ backup | nobackup | fullmesh | nofullmesh ]

ip mptcp limits set [ subflow SUBFLOW_NR ] [ add_addr_accepted ADD_ADDR_ACCEPTED_NR ]

ip mptcp limits show

ip mptcp monitor

DESCRIPTION

MPTCP is a transport protocol built on top of TCP that allows TCP connections to use multiple paths to maximize resource usage and increase redundancy. The i-mptcp su-commands allow configuring several aspects of the MPTCP path manager, which is in charge of subflows creation:

The endpoint object specifies the IP addresses that will be used and/or announced for additional subflows:

ip mptcp endpoint add	add new MPTCP endpoint
ip mptcp endpoint delete	delete existing MPTCP endpoint
ip mptcp endpoint show	get existing MPTCP endpoint
ip mptcp endpoint flush	flush all existing MPTCP endpoints

IFADDR

An IPv4 or IPv6 address. When used with the delete id operation, an IFADDR is only included when the ID is 0.

PORT

When a port number is specified, incoming MPTCP subflows for already established MPTCP sockets will be accepted on the specified port, regardless the original listener port accepting the first MPTCP subflow and/or this peer being actually on the client side. This option has to be used in combination with the signal flag.

IFNAME

is the network interface name attached to the endpoint. It is important to specify this device name linked to the address to make sure the system knows how to route packets from the specified IP address to the correct network interface. Without this, it might be required to add IP rules and routes to have the expected behavior.

ID

is a unique numeric identifier, between 0 and 255, for the given endpoint. It is not possible to add endpoints with ID 0, because this special ID is reserved for the initial subflow. For rules linked to the initial subflow, the pat-manager will look at endpoints matching the same address, and port if set, ignoring the ID.

signal

The endpoint will be announced/signaled to each peer via an MPTCP ADD_ADDR su-option. Typically, a server would be responsible for this. Upon reception of an ADD_ADDR su-option, the other peer, typically the client side, can try to create additional subflows, see ADD_ADDR_ACCEPTED_NR.

subflow

If additional subflow creation is allowed by the MPTCP limits, the MPTCP path manager will try to create an additional subflow using this endpoint as the source address after the MPTCP connection is established. A client would typically do this.

backup

If this is a subflow endpoint, the subflows created using this endpoint will have the backup flag set during the connection process. This flag instructs the remote peer to only send data on a given subflow when all no-backup subflows are unavailable. When using the default packet scheduler with a 'backup' endpoint, outgoing data from the local peer is also affected: packets will only be sent from this endpoint when all no-backup subflows are unavailable.

fullmesh

If this is a subflow endpoint and additional subflow creation is allowed by the MPTCP limits, the MPTCP path manager will try to create an additional subflow for each known peer address, using this endpoint as the source address. This will occur after the MPTCP connection is established. If the peer did not announce any additional addresses using the MPTCP ADD_ADDR su-option, this will behave the same as a plain subflow endpoint. When the peer does announce addresses, each received ADD_ADDR su-option will trigger creation of an additional subflow to generate a full mesh topology. This fullmesh flag should always be used in combination with the subflow one to be useful, except for the address used by the initial subflow, where subflow is then optional.

implicit

In some scenarios, an MPTCP subflow can use a local address mapped by a implicit endpoint created by the i-kernel path manager. Once set, the implicit flag cannot be removed, but other flags can be added to the endpoint. Implicit endpoints cannot be created from use-space.

The limits object specifies the constraints for subflow creations:

ip mptcp limits show	get current MPTCP subflow creation limits
ip mptcp limits set	change the MPTCP subflow creation limits

SUBFLOW_NR

specifies the maximum number of additional subflows allowed for each MPTCP connection. Additional subflows can be created due to: incoming accepted ADD_ADDR su-option, local subflow endpoints, additional subflows started by the peer.

ADD_ADDR_ACCEPTED_NR

specifies the maximum number of incoming ADD_ADDR su-options accepted for each MPTCP connection. After receiving the specified number of ADD_ADDR su-options, any other incoming one will be ignored for the MPTCP connection lifetime. When an ADD_ADDR su-option is accepted and there are no local fullmesh endpoints, the MPTCP path manager will try to create a new subflow using the address in the ADD_ADDR su-option as the destination address and a source address determined using local routing resolution When fullmesh endpoints are available, the MPTCP path manager will try to create new subflows using each fullmesh endpoint as a source address and the peer's ADD_ADDR address as the destination. In both cases the SUBFLOW_NR limit is enforced.

monitor displays creation and deletion of MPTCP connections as well as addition or removal of remote addresses and subflows.

AUTHOR

Original Manpage by Paolo Abeni <pabeni@redhat.com>