A method comprising: advertising a virtual Internet Protocol, IP, address (336, 431, 531, 631) shared by at least a first load balancer (365, 430, 530, 630) and a second load balancer (335, 345), the first load balancer (365, 430, 530, 630) corresponding to a first plurality of servers and the second load balancer (335, 345) corresponding to a second plurality of servers, wherein the first (365, 430, 530, 630) and second (335, 345) load balancers perform load balancing of Session Initiation Protocol, SIP, Register messages for Voice over Internet Protocol, VoIP, services offered by the first and second plurality of servers, respectively; and responsive to receiving a SIP Register message from a client (301, 305, 401, 405, 501, 505, 601, 605), the first load balancer (365, 430, 530, 630) causing the SIP Register message to be directed to a particular server of the first plurality of servers, wherein the first load balancer (365, 430, 530, 630) is determined to be closer to the client (301, 305, 401, 405, 501, 505, 601, 605) than the second load balancer (335, 345), wherein said determination that the first load balancer (365, 430, 530, 630) is closer is performed on the basis of: network metrics comprising link congestion and/or cost metrics assigned to routers, wherein said network metrics are to indicate logical closeness; or link-state information and/or routing protocols, to indicate logical closeness; or routing metrics to indicate geographic closeness, wherein said routing metrics are metrics of a target service network comprising the load balancers (365, 430, 530, 630, 335, 345). advertising a virtual Internet Protocol, IP, address (336, 431, 531, 631) shared by at least a first load balancer (365, 430, 530, 630) and a second load balancer (335, 345), the first load balancer (365, 430, 530, 630) corresponding to a first plurality of servers and the second load balancer (335, 345) corresponding to a second plurality of servers, wherein the first (365, 430, 530, 630) and second (335, 345) load balancers perform load balancing of Session Initiation Protocol, SIP, Register messages for Voice over Internet Protocol, VoIP, services offered by the first and second plurality of servers, respectively; and responsive to receiving a SIP Register message from a client (301, 305, 401, 405, 501, 505, 601, 605), the first load balancer (365, 430, 530, 630) causing the SIP Register message to be directed to a particular server of the first plurality of servers, wherein the first load balancer (365, 430, 530, 630) is determined to be closer to the client (301, 305, 401, 405, 501, 505, 601, 605) than the second load balancer (335, 345), wherein said determination that the first load balancer (365, 430, 530, 630) is closer is performed on the basis of: network metrics comprising link congestion and/or cost metrics assigned to routers, wherein said network metrics are to indicate logical closeness; or link-state information and/or routing protocols, to indicate logical closeness; or routing metrics to indicate geographic closeness, wherein said routing metrics are metrics of a target service network comprising the load balancers (365, 430, 530, 630, 335, 345). network metrics comprising link congestion and/or cost metrics assigned to routers, wherein said network metrics are to indicate logical closeness; or link-state information and/or routing protocols, to indicate logical closeness; or routing metrics to indicate geographic closeness, wherein said routing metrics are metrics of a target service network comprising the load balancers (365, 430, 530, 630, 335, 345).