Patent ID: 8606961

Claim:
A transient loop prevention method in a network having a plurality of network nodes linked to each other through interfaces and controlled by a link-state protocol, each node comprises a processor unit, the method comprising the steps of: receiving a synchronization request at a network interface; receiving a message at the network interface having a port, the message contains an advertisement at the network interface from another neighbor node which contains information on a change in the topology; blocking forwarding of traffic to each neighbor node of the network at the network interface by the processing unit and to at least an active topology or a forwarding path that is affected by the change at network interface to prevent a transient loop; agreeing by the processing unit on the change in topology with each neighbor node so there will be no transient loop by exchanging a description on a topology database or a digest of the topology database and sending a synchronization request to the other neighbor node on at least one port which contains the information on the advertisement and verifying the neighbor node has the same topology database by receiving a synchronization acknowledgment having a node ID and a sequence number of the advertisement from the neighbor node to which the synchronization request has been sent that indicates the neighbor node has updated the topology according to the topology information in the advertisement; setting a Send Routing Message Flag for each IS-IS link-state protocol data unit (PDU) per port’ setting a flag regarding blocking of a port when the advertisement contains topology change information, clearing the flag regarding blocking of a port at the reception of a Partial Sequence Numbers Protocol Data Unit (PSNP); configuring the PSNP Interval in the range of 1-10 milliseconds for fast convergence maintaining the blocking until the neighbor node agrees that it has a topology in its memory that is the same as the topology in a memory in the network node; verifying with the processing unit the advertisement has been received and processed for which the synchronization request has been sent; unblocking the forwarding of traffic when the neighbor node has information about the topology which is the same as the information about the topology stored in the topology database in the memory in the network node so there is no transient loop; and sending with the network interface a synchronization acknowledgment.