Abstract: A protocol data unit is routed along a path between a first node and a second node within a communication network. The protocol data unit carries routing information which specifies the path in the form of a list of identifiers of the links to be followed towards the second node. At each intermediate node, the link identifier for the link just traversed with a link identifier for the corresponding link in the reverse direction towards the first node. At any point along the path the protocol data unit carries information which allows it to be carried towards the second node, or to follow a reverse path towards the first node. This reverse path can be used to report a fault to the first node.

Abstract: A communication network comprises a plurality of nodes interconnected by communication links. A node maintains a database of topology information relating to the network. A node receives a topology advertisement from another node of the network which provides information about a part of the network. The topology advertisement includes a metric which is related to aggregate distance or cost of the path travelled by the topology advertisement. The node compares the metric in the newly received topology advertisement with one previously received for the same part of the network. The database is updated with the newly received topology advertisement if the value of the metric in the newly received topology advertisement is lower than the metric in the topology advertisement previously received for the same part of the network. The method can be used during flooding or database synchronisation. The metric can be carried within a header or body of a topology advertisement, such as a Link State Advertisement (LSA).