1. A method of distributing information relating to a set of networks from a first node to a second node of a communication system, wherein a set of identifiers of respective networks which belong to the set of networks is stored at the first node, the method comprising: generating, at the first node, hash values for the identifiers in the set of identifiers using a hash function; transmitting the generated hash values from the first node to the second node; the second node determining an identifier of a particular network which is available for communicating with the second node; generating, at the second node, a hash value for the identifier of the particular network using said hash function; and comparing, at the second node, the hash value of the identifier of the particular network generated at the second node with the hash values received at the second node from the first node to thereby determine whether the particular network belongs to said set of networks.