A method for communication is used in a communication network that
includes multiple ring nodes arranged in at least first and second ring
networks, which are connected by one or more of the ring nodes serving as
interconnect nodes. A data packet is accepted from a source user node
served by the first ring network, for forwarding to a destination user
node served by the second ring network. An identifier, which identifies
an interconnect node in the first ring network through which the data
packet is to be forwarded to the second ring network, is attached to the
data packet in the first ring network. The data packet is forwarded over
the first ring network, accepted at the interconnect node and,
responsively to the identifier, forwarded from the interconnect node to
the second ring network. The data packet is forwarded over the second
ring network to the destination user node.