Implementations of the present disclosure include identifying, by a relay that is communicatively linked with a first blockchain instance and a second blockchain instance in a unified blockchain network, a blockchain domain name of a first blockchain instance; identifying a blockchain domain name of the second blockchain instance; receiving, from a node of the first blockchain instance, an access request for accessing the second blockchain instance, wherein the access request including the blockchain domain name of the second blockchain instance; identifying a chain identifier of the second blockchain instance based on the blockchain domain name of the second blockchain instance, wherein the chain identifier of the second blockchain instance indicates a blockchain network configuration of the second blockchain instance; and providing access to the second blockchain instance for the first blockchain instance based on the blockchain network configuration indicated by the chain identifier of the second blockchain instance.