Translating MST instances between ports of a bridge in a computer network

1. A method, comprising:

configuring a first port of a bridge for a first spanning tree (ST);

configuring a second port of the bridge for a second ST, the second port interconnected with the first port;

generating, for the first port, a first multiple ST (MST) bridge protocol data unit (BPDU) for the first and second STs, the first MST BPDU having a first portion corresponding to the first ST and a second portion corresponding to the second ST;

generating, for the second port, a second MST BPDU for the first and second STs, the second MST BPDU having a first portion corresponding to the first ST and a second portion corresponding to the second ST;

stripping the second portion from the first MST BPDU of the first port;

associating the first portion from the first MST BPDU of the first port with the second ST;

stripping the first portion from the second MST BPDU of the second port; and

associating the second portion from the second MST BPDU of the second port with the first ST.

2. The method as in claim 1 , further comprising:

performing the stripping and associating for the first port on the first port; and

performing the stripping and associating for the second port on the second port.

3. The method as in claim 1 , further comprising:

performing the stripping and associating for the first and second ports on one of either the first or second port.

4. The method as in claim 1 , further comprising:

transmitting each MST BPDU between the first and second ports.

5. The method as in claim 1 , wherein the first and second ports are a single port, the method further comprising:

inserting the first MST BPDU for the first port to a receive queue of the second port; and

inserting the second MST BPDU for the second port to a receive queue of the first port.

6. The method as in claim 1 , wherein the first ST represents a first virtual local area network (VLAN) and the second ST represents a second VLAN.

7. The method as in claim 6 , wherein the bridge is a first virtual bridge for the first VLAN and a second virtual bridge for the second VLAN.

8. The method as in claim 1 , wherein a service device is interconnected between the first and second ports.

9. The method as in claim 8 , wherein the service device is selected from the group consisting of: a firewall, an intrusion detection system (IDS), and a load-balancer.

10. The method as in claim 1 , wherein the first and second portions are MRecords of each MST BPDU.

11. The method as in claim 1 , wherein the first and second ports are interconnected internally within the bridge.

12. An apparatus, comprising:

a first port configured for a first spanning tree (ST) and not a second ST;

a second port configured for a second ST, the second port interconnected with the first port;

a processor coupled to the first and second ports and adapted to execute one or more processes; and

a memory adapted to store an instance translation process executable by the processor, the instance translation process when executed operable to:

generate, for the first port, a first multiple ST (MST) bridge protocol data unit (BPDU) for the first and second STs, the first MST BPDU having a first portion corresponding to the first ST and a second portion corresponding to the second ST;

generate, for the second port, a second MST BPDU for the first and second STs, the second MST BPDU having a first portion corresponding to the first ST and a second portion corresponding to the second ST;

strip the second portion from the first MST BPDU of the first port;

associate the first portion from the first MST BPDU of the first port with the second ST;

strip the first portion from the second MST BPDU of the second port; and

associate the second portion from the second MST BPDU of the second port with the first ST.

13. The apparatus as in claim 12 , wherein the instance translation process operates on the first port for the first MST BPDU for the first port, and also operates on the second port for the second MST BPDU for the second port.

14. The apparatus as in claim 12 , wherein the instance translation process operates on one of either the first or second port for the MST BPDU for the first and second ports.

15. The apparatus as in claim 12 , wherein the first and second ports are a single port, the apparatus further comprising:

a first receive queue of the first port;

a second receive queue of the second port; and

wherein the instance translation process is further operable to insert the first MST BPDU for the first port to the second receive queue of the second port and to insert the second MST BPDU for the second port to the first receive queue of the first port.

16. The apparatus as in claim 15 , wherein the single port is a trunk port of the apparatus.

17. The apparatus as in claim 12 , wherein the first ST represents a first virtual local area network (VLAN) and the second ST represents a second VLAN, and the apparatus is a first virtual bridge for the first VLAN and a second virtual bridge for the second VLAN.

18. The apparatus as in claim 12 , wherein a service device is interconnected between the first and second ports.

19. The apparatus as in claim 12 , wherein the first and second ports are interconnected internally within the apparatus.

20. A method, comprising:

configuring a first port of a bridge for a first spanning tree (ST) and not a second ST;

configuring a second port of the bridge for the second ST and not the first ST, the second port interconnected with the first port;

generating a multiple ST (MST) bridge protocol data unit (BPDU) for the first and second STs for the first port, the MST BPDU having a first portion corresponding to the first ST and a second portion corresponding to the second ST;

stripping the second portion from the MST BPDU of the first port;

associating the first portion from the MST BPDU of the first port with the second ST; and

transmitting the MST BPDUs from the first port to the second port.