1. A method performed by an X2 gateway apparatus in a communication system comprising the X2 gateway apparatus and a plurality of base stations, the method comprising:establishing a respective Stream Control Transmission Protocol (SCTP) association between the X2 gateway apparatus and each base station connected to the X2 gateway apparatus:
maintaining, for each base station connected to the X2 gateway apparatus, respective association information indicating a mapping of an identifier for the base station to at least one Transport Network Layer (TNL) address for the base station;
receiving, from a source base station, over an X2 interface using the SCTP association between the X2 gateway apparatus and the source base station, when the source base station's TNL address changes, an X2 message to initiate registration with the X2 gateway apparatus, the X2 message comprising said identifier for said source base station, wherein said identifier comprises an information element based on an E-UTRAN Cell Global Identifier (ECGI) of said source base station; and
updating said association information, based on information included in said X2 message to initiate registration, to reflect a mapping to at least one TNL address of the base station from which the X2 message to initiate registration originated.