Presently only IP packets are supported by opencontrail for ECMP load balancing which can be further extended to GTP-U packets.

# 1. Introduction
#### Purpose of the document
Presently only IP packets are supported by opencontrail for ECMP load balancing which can be further extended to GTP-U packets.

# 2. Problem statement
#### Describe the problem being solved for a new or existing features.
In LTE core network, GTP-U packets are sent to and from mobile equipment. Opencontrail ECMP load balancer cannot handle GTP-U traffic for load balancing.

#### Use cases
Opencontrail can be used to balance GTP-U traffic in LTE core network using existing ECMP algorithms.

# 3. Proposed solution
#### Describe the proposed solution.
To achieve load balancing, Routers use a 4-tuple source IP address, destination IP address, L4 source and destination port (if traffic is TCP or UDP),
and fields from the packet. However, for GTP traffic, the presence of limited number of unique values for these fields restricts the equal distribution
of traffic load on the tunnel. To avoid polarization for GTP traffic in load balancing, a tunnel endpoint identifier (TEID) in the GTP header is used
instead of the UDP port number. Because TEID is unique per tunnel, traffic can be evenly load balanced across ECMPs. This feature allows you to look
inside the GTP header and balance the traffic over ECMP on a per subscriber basis. To implement load balancing for GTP-encapsulated traffic on the user
plane (GTP-U), the TEID should be included in the hash key. If message type is T-PDU and UDP port is 2152, the GTP-U traffic should be load balanced.
instead of the UDP port number. Because TEID is unique per tunnel, traffic can be evenly load balanced across ECMPs. This feature allows you to look
inside the GTP header and balance the traffic over ECMP on a per subscriber basis. To implement load balancing for GTP-encapsulated traffic on the user
plane (GTP-U), the TEID should be included in the hash key. If message type is T-PDU and UDP port is 2152, the GTP-U traffic should be load balanced.