Interior gateway protocol flood minimization

1. A method implemented in a first node in a network, the method comprising:

receiving, at a receiver of the first node, data indicating connectivity of a plurality of nodes in the network including the first node;

building, by a processor of the first node, a flooding topology based on the connectivity by:

selecting one of the plurality of nodes as a root node, and

building a tree of links connecting the root node to other nodes in the network according to an algorithm, wherein the algorithm is contained in an algorithm field of a received link state message;

storing the flooding topology in a memory; and

flooding, by a transmitter of the first node, link state messages over the flooding topology.

2. The method of claim 1 , further comprising:

receiving, at the receiver, a request specifying a number of leaf links to add to the tree; and

adding to the flooding topology, by the processor, the number of leaf links between the plurality of nodes in the network.

3. The method of claim 1 , wherein, prior to adding leaf links, the tree of links in the flooding topology contains a minimum number of links to connect all of the plurality of nodes in the network to the root node.

4. The method of claim 1 , further comprising:

establishing, by the processor, an adjacency with a newly connected node, wherein the newly connected node is directly connected to the first node via a link; and

adding, by the processor, the newly connected node to the tree of links in the flooding topology until the flooding topology is recomputed.

5. The method of claim 1 , further comprising:

receiving, at the receiver, a first link state message across a link that is excluded from the flooding topology; and

flooding, by the transmitter, the first link state message across links on the flooding topology.

6. The method of claim 1 , further comprising:

receiving, at the receiver, a second link state message indicating a second node in the network is down; and

flooding, by the transmitter, the second link state message to links that connect between the first node and neighbors of the second node.

7. The method of claim 1 , further comprising:

receiving, at the receiver, a third link state message indicating a first link in the network is down;

determining that the first link is a critical element; and

based on the determination, sending the third link state message to links that connect to neighbors which also connect nodes adjacent to a node attached to the first link.

8. The method of claim 1 , further comprising:

determining, by the processor, critical elements, wherein a critical element is a link or node whose failure splits the flooding topology; and

discontinue use of the flooding topology when a critical interface fails.

9. The method of claim 1 , wherein the link state messages are Open Shortest Path First (OSPF) Link State Advertisements (LSAs), or Intermediate System to Intermediate System (IS-IS) Link State Protocol data units (LSPs).

10. The method of claim 1 , wherein the link state messages contain at least one of the following:

flooding reduction (F) flags set to indicate the plurality of nodes in the network that support link state flooding reduction via the flooding topology;

a mode field set to indicate centralized link state flooding reduction, distributed link state flooding reduction, or statically configured link state flooding reduction;

an algorithm field set to indicate an algorithm to build the tree of links in the flooding topology; or

an operation (OP) field set to switch to link state flooding reduction from full network flooding.

11. A first node in a network, the first node comprising:

a receiver configured to receive data indicating connectivity of a plurality of nodes in the network including the first node;

a processor coupled to the receiver, the processor configured to:

build a flooding topology based on the connectivity by:

selecting one of the plurality of nodes as a root node, and

building a tree of links connecting the root node to other nodes in the network according to an algorithm, wherein the algorithm is contained in an algorithm field of a received link state message;

a memory coupled to the processor, the memory configured to store the flooding topology; and

a transmitter coupled to the processor, the transmitter configured to flood link state messages over the flooding topology.

12. The first node of claim 11 , wherein the receiver is further configured to receive a request specifying a number of leaf links to add to the tree, and wherein the processor is further configured to add to the flooding topology the number of leaf links between the plurality of nodes in the network.

13. The first node of claim 11 , wherein, prior to adding leaf links, the tree of links in the flooding topology contains a minimum number of links to connect all of the plurality of nodes in the network to the root node.

14. The first node of claim 11 , wherein the processor is further configured to establish an adjacency with a newly connected node, wherein the newly connected node is directly connected to the first node via a link, and wherein the processor is further configured to add the newly connected node to the tree of links in the flooding topology until the flooding topology is recomputed.

15. The first node of claim 11 , wherein the receiver is further configured to receive a first link state message across a link that is excluded from the flooding topology, and wherein the transmitter is further configured to flood the first link state message across links on the flooding topology.

16. The first node of claim 11 , wherein the receiver is further configured to receive a second link state message indicating a second node in the network is down, and wherein the transmitter is further configured to flood the second link state message to links that connect between the first node and neighbors of the second node.

17. The first node of claim 11 , wherein the receiver is further configured to receive a third link state message indicating a first link in the network is down, wherein the processor is further configured to determine that the first link is a critical element, and wherein the transmitter is further configured to, based on the determination, send the third link state message to links that connect to neighbors which also connect to neighbor nodes adjacent to a node attached to the first link.

18. The first node of claim 11 , wherein the processor is further configured to:

determine critical elements, wherein a critical element is a link or node whose failure splits the flooding topology; and

discontinue use of the flooding topology when a critical element fails.

19. The first node of claim 11 , wherein the link state messages are Open Shortest Path First (OSPF) Link State Advertisements (LSAs), or Intermediate System to Intermediate System (IS-IS) Link State Protocol data units (LSPs).

20. The first node of claim 11 , wherein the link state messages contain at least one of the following:

flooding reduction (F) flags set to indicate the plurality of nodes in the network that support link state flooding reduction via the flooding topology;

a mode field set to indicate centralized link state flooding reduction, distributed link state flooding reduction, or statically configured link state flooding reduction;

an algorithm field set to indicate an algorithm to build the tree of links in the flooding topology; or

an operation (OP) field set to switch to link state flooding reduction from full network flooding.

21. A non-transitory computer readable medium comprising a computer program product for use by a first node in a network, the computer program product comprising computer executable instructions stored on the non-transitory computer readable medium such that when executed by a processor cause the first node to:

receive data indicating connectivity of a plurality of nodes in the network including the first node;

build a flooding topology based on the connectivity by selecting one of the plurality of nodes as a root node, and building a tree of links connecting the root node to other nodes in the network according to an algorithm, wherein the algorithm is contained in an algorithm field of a received link state message;

store the flooding topology; and

flood link state messages over the flooding topology.