A method of operating a first router device forming a node (10, 20, 30) within a packet switched data network of the type in which a number of router devices (10, 20, 30) forward received packets of data towards a destination node using a packet-switched network, or inter-network, protocol, the method comprising: maintaining a routing table, indicating the next hop to choose in respect of different ultimate destinations, in accordance with a dynamic routing protocol; and monitoring the time elapsed since the most recent receipt of at least one type of status-indicating packet in respect of an active neighbouring router device (20, 30) and determining that the neighbouring router device (20, 30), or the currently designated route thereto, has gone down in the event that the monitored time elapsed exceeds a router dead interval; and characterised by monitoring the time of receipt of said status-indicating packets; generating a value for the average arrival interval of said status-indicating packets; periodically calculating the ratio of the monitored time elapsed to the average arrival interval, and reducing the router dead interval from its default value in accordance with an inverse function of that ratio; and wherein said at least one type of status-indicating packet includes any one or more of the following types of packets: received packets destined for a node other than the first router device, received packets originating from a node other than the respective neighbouring router device (20, 30); or received packets both originating from a node other than the respective neighbouring router device and destined for a node other than the first router device. maintaining a routing table, indicating the next hop to choose in respect of different ultimate destinations, in accordance with a dynamic routing protocol; and monitoring the time elapsed since the most recent receipt of at least one type of status-indicating packet in respect of an active neighbouring router device (20, 30) and determining that the neighbouring router device (20, 30), or the currently designated route thereto, has gone down in the event that the monitored time elapsed exceeds a router dead interval; and characterised by monitoring the time of receipt of said status-indicating packets; generating a value for the average arrival interval of said status-indicating packets; periodically calculating the ratio of the monitored time elapsed to the average arrival interval, and reducing the router dead interval from its default value in accordance with an inverse function of that ratio; and wherein calculating the ratio of the monitored time elapsed to the average arrival interval, and reducing the router dead interval from its default value in accordance with an inverse function of that ratio; and wherein said at least one type of status-indicating packet includes any one or more of the following types of packets: received packets destined for a node other than the first router device, received packets originating from a node other than the respective neighbouring router device (20, 30); or received packets both originating from a node other than the respective neighbouring router device and destined for a node other than the first router device.