An add and drop node for a WDM optical network comprising: an optical input section adapted to be connected to a first network segment for receiving a plurality of first optical packets on a plurality of wavelength channels (λ1-λ4), a drop module for demodulating optical packets selected as a function of control data, an optical output section adapted to be connected to a second network segment, a selective transit section arranged between the optical input section and the optical output section for passing a first subset of the first optical packets to the optical output section and preventing a second subset of the first optical packets from reaching the optical output section, wherein the wavelength selective transit section comprises a wavelength demultiplexer, a wavelength multiplexer and a plurality of lines each dedicated to a wavelength channel and each connecting an output of the wavelength demultiplexer to an input of the wavelength multiplexer, an optical gate being arranged on each dedicated line and controlled on a packet-by-packet basis for selectively passing or blocking each optical packet as a function of the control data, an add module for generating second optical packets adapted for superimposition to the first subset of the first optical packets for WDM transmission to the second network segment, wherein the second optical packets are synchronized with the first optical packets, a traffic controller adapted to receive the control data relating to the first optical packets from the first network segment and to transmit control data relating to the first subset of the first optical packets and the second optical packets to the second network segment, characterized by a failure detection module for detecting a failure state of the first network segment, and a light source (51, 66) adapted to generate time-continuous optical power in the input section in response to detection of the failure state, the optical power being generated in a spectrum including the plurality of wavelength channels, wherein the optical gate dedicated to a wavelength channel is controlled by the traffic controller to create gaps during time intervals reserved for the second optical packets and to shape the time-continuous optical power into dummy optical packets during the remaining time intervals, wherein the wavelength demultiplexer is adapted to filter the optical power in frequency to pass a narrow range of frequencies to each dedicated line. an optical input section adapted to be connected to a first network segment for receiving a plurality of first optical packets on a plurality of wavelength channels (λ1-λ4), a drop module for demodulating optical packets selected as a function of control data, an optical output section adapted to be connected to a second network segment, a selective transit section arranged between the optical input section and the optical output section for passing a first subset of the first optical packets to the optical output section and preventing a second subset of the first optical packets from reaching the optical output section, wherein the wavelength selective transit section comprises a wavelength demultiplexer, a wavelength multiplexer and a plurality of lines each dedicated to a wavelength channel and each connecting an output of the wavelength demultiplexer to an input of the wavelength multiplexer, an optical gate being arranged on each dedicated line and controlled on a packet-by-packet basis for selectively passing or blocking each optical packet as a function of the control data, an add module for generating second optical packets adapted for superimposition to the first subset of the first optical packets for WDM transmission to the second network segment, wherein the second optical packets are synchronized with the first optical packets, a traffic controller adapted to receive the control data relating to the first optical packets from the first network segment and to transmit control data relating to the first subset of the first optical packets and the second optical packets to the second network segment, characterized by a failure detection module for detecting a failure state of the first network segment, and a light source (51, 66) adapted to generate time-continuous optical power in the input section in response to detection of the failure state, the optical power being generated in a spectrum including the plurality of wavelength channels, wherein the optical gate dedicated to a wavelength channel is controlled by the traffic controller to create gaps during time intervals reserved for the second optical packets and to shape the time-continuous optical power into dummy optical packets during the remaining time intervals, wherein the wavelength demultiplexer is adapted to filter the optical power in frequency to pass a narrow range of frequencies to each dedicated line.