Service chaining across multiple networks

In some examples, a controller comprises one or more processors; a control unit configured to obtain, from a router in a first network, a route that specifies a next hop to an address prefix reachable by the first network; and a service chain unit configured to generate a modified route that specifies a service node as the next hop for the address prefix, wherein the service node is external to the first network, and wherein the control unit is further configured to send the modified route to a second network, the modified route marked with an import route target configured for a provider edge router of the second network so that traffic from the first network and destined for the second network is forwarded to the service node.