A method implemented at a primary Network-Function Repository Function, NRF, in a communication network, the method comprising: receiving a discovery request from a first secondary NRF (NRF#1), wherein the discovery request comprises a service query information for a target Network Function, NF, obtaining target NF information; providing the target NF information to the first secondary NRF (NRF#1); wherein obtaining target NF information comprises: sending the discovery request to at least one of other secondary NRFs (NRF#2); and receiving a response from at least one of other secondary NRFs (NRF#2...n), wherein the response comprises an indication of whether the other secondary NRFs (NRF#2), contains the target NF information; and if the indication represents that the other secondary NRF (NRF#2) contains the target NF information, the response further comprises the target NF information and/or the information of the other secondary NRF, the method further comprising: receiving registration information from one or more secondary NRFs; sending the discovery request to at least one of other secondary NRFs (NRF#2...n), and wherein the obtaining target NF information is based on the registration information; maintaining routing table information for mapping the information of the secondary NRFs (NRF#2...n); sending the discovery request to at least one of other secondary NRFs (NRF#2... n) and the information of NFs which are registered in the corresponding NRF; and updating the routing table based on the registration information. receiving a discovery request from a first secondary NRF (NRF#1), wherein the discovery request comprises a service query information for a target Network Function, NF, obtaining target NF information; providing the target NF information to the first secondary NRF (NRF#1); wherein obtaining target NF information comprises: sending the discovery request to at least one of other secondary NRFs (NRF#2); and receiving a response from at least one of other secondary NRFs (NRF#2...n), wherein the response comprises an indication of whether the other secondary NRFs (NRF#2), contains the target NF information; and if the indication represents that the other secondary NRF (NRF#2) contains the target NF information, the response further comprises the target NF information and/or the information of the other secondary NRF, the method further comprising: receiving registration information from one or more secondary NRFs; sending the discovery request to at least one of other secondary NRFs (NRF#2...n), and wherein the obtaining target NF information is based on the registration information; maintaining routing table information for mapping the information of the secondary NRFs (NRF#2...n); sending the discovery request to at least one of other secondary NRFs (NRF#2... n) and the information of NFs which are registered in the corresponding NRF; and updating the routing table based on the registration information. sending the discovery request to at least one of other secondary NRFs (NRF#2); and receiving a response from at least one of other secondary NRFs (NRF#2...n), wherein the response comprises an indication of whether the other secondary NRFs (NRF#2), contains the target NF information; and if the indication represents that the other secondary NRF (NRF#2) contains the target NF information, the response further comprises the target NF information and/or the information of the other secondary NRF, the method further comprising: receiving registration information from one or more secondary NRFs; sending the discovery request to at least one of other secondary NRFs (NRF#2...n), and wherein the obtaining target NF information is based on the registration information; maintaining routing table information for mapping the information of the secondary NRFs (NRF#2...n); sending the discovery request to at least one of other secondary NRFs (NRF#2... n) and the information of NFs which are registered in the corresponding NRF; and updating the routing table based on the registration information. receiving registration information from one or more secondary NRFs; sending the discovery request to at least one of other secondary NRFs (NRF#2...n), and wherein the obtaining target NF information is based on the registration information; maintaining routing table information for mapping the information of the secondary NRFs (NRF#2...n); sending the discovery request to at least one of other secondary NRFs (NRF#2... n) and the information of NFs which are registered in the corresponding NRF; and updating the routing table based on the registration information.