Method and apparatus for determining a spanning tree
View Patent ↗It is realized that the use of a spanning tree protocol in particular portions of a network may not necessarily be desired due to performance and stability reasons. A method and system is provided for executing a revised spanning tree algorithm that performs more optimally in particular network topologies. In one aspect, a spanning tree protocol is executed over a first and second network connected by a third network, wherein the spanning tree network is disabled in the third network. The third network may be, for example, a core network through which first and second Layer 2 networks are bridged. The first and second networks may be coupled by another network or network connection, and it may be preferable to allow the operation of the spanning tree network between the first and second coupled networks for the purpose of fail over to redundant paths. In network forwarding devices positioned at edges of the core network, the operation of the STP over interfaces where network tunnels of each network forwarding device attached to the core network may be inhibitied (e.g., turned off). A phantom root bridge may be created that does not correspond to an actual network forwarding node, and this phantom root bridge may have a bridge identifier which is used by network forwarding nodes as the root bridge. In this manner, STP protocols may work as intended in peripheral networks, while STP does not need to be executed in the core.
1. A method for determining a spanning tree, the method comprising acts of:
determining a root bridge identifier, the root bridge identifier being used as a root bridge identifier in a plurality of network forwarding devices, the plurality of network forwarding devices including a first network forwarding device and a second network forwarding device participating in a network the first network forwarding device including at least one first port not running spanning tree protocol, the second network forwarding device including at least one second port not running the spanning tree protocol, the first network forwarding device coupled to the second network forwarding device through a core network via the at least one first port and the at least one second port;
storing, by the first network forwarding device and the second network forwarding device, the root bridge identifier without exchanging the root bridge identifier in a spanning tree protocol message; and
using, by the first network forwarding device and the second network forwarding device, the root bridge identifier before and after reconfiguration of the spanning tree, wherein the first network forwarding device exchanges data packets with the second network forwarding device through the core network via the at least one first port and the at least one second port before and after the reconfiguration of the spanning tree.
2. The method according to claim 1 , wherein the act of determining the root bridge identifier includes an act of configuring, at the first network forwarding device and the second network forwarding device, the root bridge identifier as being the root bridge in the spanning tree.
3. The method according to claim 1 , further comprising an act of configuring, at the first network forwarding device and the second network forwarding device, a same root bridge path cost.
4. The method according to claim 1 , wherein the act of determining a root bridge identifier further comprises an act of configuring, in a first respective memory of the first network forwarding device and a second respective memory of the second network forwarding device, an entry for the root bridge identifier.
5. The method according to claim 1 , further comprising an act of determining, for at least one first respective access port of the first network forwarding device and at least one second respective access port of the second network forwarding device, a root path cost.
6. The method according to claim 5 , wherein the root path costs for the at least one first respective access port and the at least one second respective access port are the same value.
7. The method according to claim 5 , wherein the core network includes a bridged network that couples the first network forwarding device to the second network forwarding device, and wherein the method further comprises an act of disabling, on the at least one first port and the at least one second port, transmission of bridge protocol data units (BPDUs) between the first network forwarding device and the second network forwarding device.
8. The method according to claim 7 , wherein the bridged network is implemented using Multiprotocol Label Switching (MPLS).
9. The method according to claim 7 , further comprising an act of transmitting, on the at least one first respective access port and the at least one second respective access port, bridge protocol data units (BPDUs).
10. The method according to claim 9 , wherein the first network forwarding device and the second network forwarding device are coupled by another network, and the method further comprises communicating the root bridge identifier in at least one BPDU transmitted on the another network.
11. The method according to claim 5 , wherein the core network includes a bridged network that couples the first network forwarding device to the second network forwarding device, and wherein the method further comprises an act of disabling, on at least one first logical connection of the first network forwarding device coupled to the bridged network and at least one second logical connection of the second network forwarding device coupled to the bridged network, transmission of bridge protocol data units (BPDUs) between the first network forwarding device and the second network forwarding device.
12. The method according to claim 11 , wherein the bridged network is implemented using Multiprotocol Label Switching (MPLS).
13. The method according to claim 11 , further comprising an act of transmitting, on at least one first respective access port of the first network forwarding device and at least one second respective access port of the second network forwarding device, bridge protocol data units (BPDUs).
14. The method according to claim 13 , wherein the first network forwarding device and the second network forwarding device are coupled by another network, and the method further comprises communicating the root bridge identifier in at least one BPDU transmitted on the another network.
15. The method according to claim 1 , wherein the first network forwarding device and the second network forwarding device are located at the edge of a provider network, and wherein the method further comprises an act of disabling, on at least one first respective port of the first network forwarding device and on at least one second respective port of the second network forwarding device, each of the first and second respective ports being coupled to the provider network, transmission of bridge protocol data units (BPDUs) between the first network forwarding device and the second network forwarding device.
16. The method according to claim 1 , wherein the root bridge identifier is not assigned to any network forwarding device in the spanning tree.
17. The method according to claim 1 , further comprising:
receiving, by the first network forwarding device, a first Topology Change Notification (TCN);
setting, responsive to receiving the first TCN, a first Topology Change (TC) Flag within a first bridge protocol data unit (BPDU);
transmitting, by the first network forwarding device, the first BPDU;
receiving, by the second network forwarding device, a second TCN;
setting, responsive to receiving the second TCN, a second TC Flag within a second BPDU; and
transmitting, by the second network forwarding device, the second BPDU.