A method in an ad hoc network comprising a plurality of nodes (1, 2, 3), the method comprising: i) a node transmitting a first neighbour discovery message, comprising a first allowable hold time value indicating how long other nodes should be prepared to wait for a further neighbour discovery message whilst still considering that a link to and from the node is intact, to a further node; and ii) the further node transmitting a second neighbour discovery message, comprising a second allowable hold time value indicating how long other nodes should be prepared to wait for a further neighbour discovery message whilst still considering that a link to and from the further node is intact, to the node; a bidirectional link between the node and the further node thereby being provided by the steps i) and ii); iii) the node transmitting a third neighbour discovery message, comprising a third allowable hold time value indicating how long other nodes should be prepared to wait for a further neighbour discovery message whilst still considering that a link to and from the node is intact, to the further node, the third allowable hold time being an extended allowable hold time compared to the first allowable hold time; iv) the further node transmitting a fourth neighbour discovery message, comprising a fourth allowable hold time value indicating how long other nodes should be prepared to wait for a further neighbour discovery message whilst still considering that a link to and from the further node is intact, to the node, the fourth allowable hold time value being the same as, or less than, the second allowable hold time; v) the node changing its transmission behaviour such that the further node stops receiving transmission from the node for an extended period; a unidirectional link from the further node to the node thereby being provided by the steps iii), iv) and v); and further comprising the node being instructed to maintain topology information for an extended time, wherein the method is performed responsive to a threat located at a position relative to the positions of the node and the further node that means it is not desired to transmit in a direction from the node to the further node but it is desired or acceptable to transmit in a direction from the further node to the node. i) a node transmitting a first neighbour discovery message, comprising a first allowable hold time value indicating how long other nodes should be prepared to wait for a further neighbour discovery message whilst still considering that a link to and from the node is intact, to a further node; and ii) the further node transmitting a second neighbour discovery message, comprising a second allowable hold time value indicating how long other nodes should be prepared to wait for a further neighbour discovery message whilst still considering that a link to and from the further node is intact, to the node; a bidirectional link between the node and the further node thereby being provided by the steps i) and ii); iii) the node transmitting a third neighbour discovery message, comprising a third allowable hold time value indicating how long other nodes should be prepared to wait for a further neighbour discovery message whilst still considering that a link to and from the node is intact, to the further node, the third allowable hold time being an extended allowable hold time compared to the first allowable hold time; iv) the further node transmitting a fourth neighbour discovery message, comprising a fourth allowable hold time value indicating how long other nodes should be prepared to wait for a further neighbour discovery message whilst still considering that a link to and from the further node is intact, to the node, the fourth allowable hold time value being the same as, or less than, the second allowable hold time; v) the node changing its transmission behaviour such that the further node stops receiving transmission from the node for an extended period; a unidirectional link from the further node to the node thereby being provided by the steps iii), iv) and v); and further comprising the node being instructed to maintain topology information for an extended time, wherein the method is performed responsive to a threat located at a position relative to the positions of the node and the further node that means it is not desired to transmit in a direction from the node to the further node but it is desired or acceptable to transmit in a direction from the further node to the node.