Multicast optimization in a VLAN tagged network

• US 20040125803A1
• Filed: 11/14/2003
• Published: 07/01/2004
• Est. Priority Date: 12/31/2002
• Status: Active Grant

• Current Assignee: Alcatel-Lucent SA (Nokia Corporation)
• Original Assignee: Alcatel-Lucent SA (Nokia Corporation)
• Inventors: Thomas, Jeffrey Glenn, Sangroniz, Robert Leon, Fine, Mark Armand, Garff, Jeremy Lynn
• Granted Patent: US 7,512,124 B2
• Time in Patent Office: Days
• US Class Current: 370/390
• CPC Class Codes: H04L 12/185 with management of multicast group membership
• CPC Class Codes: H04L 12/1886 with traffic restrictions for efficiency improvement, e.g. involving subnets or subdomains
• CPC Class Codes: H04L 12/4641 Virtual LANs, VLANs, e.g. virtual private networks [VPN] LAN interconnection over a bridge based backbone H04L12/462; encapsulation techniques H04L12/4633; routing of packets H04L45/00; packet switches H04L49/00; virtual private networks for security H04L63/0272
• CPC Class Codes: H04L 12/4645 Details on frame tagging routing of packets H04L45/00; support for virtual LAN H04L49/354
• CPC Class Codes: H04L 45/04 Interdomain routing, e.g. hierarchical routing
• CPC Class Codes: H04L 45/16 Multipoint routing

Abstract

A method and apparatus for optimizing multicast traffic in a VLAN-tagged environment is disclosed. The method, implemented by a cross-VLAN switching device, comprises the steps of receiving a multicast stream within a first VLAN of a plurality of VLANs configured thereon, and internally distributing the multicast stream towards substantially all the multicast group members registered at the cross-VLAN switching device to receive the multicast stream. Distribution of the multicast stream preferably comprises the steps of internally routing the multicast stream from the first VLAN to each VLAN in which there is a multicast group member registered to receive the multicast stream and then switching the multicast stream from each VLAN in which it is present in a cross-VLAN switching device to substantially all of the multicast group members registered to receive the multicast stream. In accordance with the invention, only a single copy of a multicast stream propagates across said one or more VLAN-tagged communications links, thereby avoiding one or more duplicative multicast streams that generally occur when there are multicast group members in a plurality of VLANs.

Claims

1. A multicast optimization method in a cross-VLAN switching device operatively coupled to one or more multicast group members configured in a plurality of VLANs and to one or more nodes via a VLAN-tagged communications link;

the method comprising the steps of;

(a) receiving a multicast stream within a first VLAN of the plurality of VLANs; and

(b) internally distributing the multicast stream toward substantially all the multicast group members registered at the cross-VLAN switching device to receive the multicast stream;

wherein a single copy of the one or more multicast streams propagates across said one or more VLAN-tagged communications links.

2. The multicast optimization method in claim 1, wherein the step of internally distributing the multicast stream to substantially all the multicast group members comprises the steps of:

(a) internally routing the multicast stream from the first VLAN to each VLAN in which there is a multicast group member registered to receive the multicast stream; and

(b) switching the multicast stream from each VLAN in which it is present in a cross-VLAN switching device towards substantially all of the multicast group member registered to receive the multicast stream.

3. The multicast optimization method in claim 2, wherein the step of routing the multicast stream comprises the step of decrementing the time-to-live counter of the packets of the multicast stream.

4. The multicast optimization method in claim 1, wherein the method further includes the step of registering the one or more multicast group members at the cross-VLAN switching device, each registration constituting a subscription to the multicast stream.

5. The multicast optimization method in claim 4, wherein the step of registering the one or more multicast group members at the cross-VLAN switching device comprises the step of recording multicast group members subscriptions in one or more VLAN/multicast group membership tables.

6. The multicast optimization method in claim 5, wherein the one or more VLAN/multicast group membership tables of the cross-VLAN switching device associate a multicast address and an IP address of the one or more multicast group members.

7. The multicast optimization method in claim 4, wherein the method further includes the step of receiving, prior to the step of registering, a multicast declaration message from a plurality of said one or more multicast group members.

8. The multicast optimization method in claim 7, wherein the multicast declaration message from the plurality of said multicast group members is an IGMP Membership Report message.

9. The multicast optimization method in claim 7, wherein the method further includes the step of forwarding only the first multicast declaration message of the plurality of multicast declaration messages upstream towards a root router.

10. The multicast optimization method in claim 4, wherein the method further includes the step of de-registering a multicast group member at the cross-VLAN switching device, each de-registration constituting a rescission of the subscription to an associated multicast stream.

11. The multicast optimization method in claim 10, wherein the method further comprises the step of receiving, prior to de-registering a multicast group member, a leave message from a plurality of the one or more multicast group members to rescind the subscription to the associated multicast stream.

12. The multicast optimization method in claim 11, wherein the leave message is an IGMP Leave message.

13. The multicast optimization method in claim 11, wherein the method further comprises the step of forwarding only the last leave message of the plurality of leave messages towards an upstream router.

14. The multicast optimization method in claim 13, wherein the last leave message of the plurality of leave messages includes a VLAN identification of the first VLAN.

16. The multicast optimization method in claim 14, wherein the step of distributing the multicast stream towards substantially all of the one or more multicast group members comprises the steps of:

(a) routing the multicast stream from the first VLAN to each of the one or more VLANs outside of the first VLAN associated with the one or more multicast group members; and

(b) switching the multicast stream towards from the cross-VLAN switching device to substantially all the one or more multicast group members associated with the one or more VLANs outside of the first VLAN.

17. The multicast optimization method in claim 14, wherein the method further includes the step of switching substantially all unicast packets from the cross-VLAN switching device to each of the nodes specified in the respective unicast packet.

18. The multicast optimization method in claim 14, wherein the step of registering each of the plurality of multicast group members further comprises the step of recording multicast subscriptions in one or more VLAN/multicast group membership tables.

19. The multicast optimization method in claim 14, wherein the method further includes the step of de-registering a first multicast group member of the one or more multicast group members from the cross-VLAN switching device, wherein the subscription to the multicast stream is rescinded.

20. The multicast optimization method in claim 18, wherein the step of de-registering occurs in response to a leave message from a first multicast group member of the one or more multicast group members.

21. The multicast optimization method in claim 19, wherein the leave message is an IGMP Leave message.

22. The multicast optimization method in claim 20, wherein the method further includes the step of forwarding only the last leave message of the plurality leave messages of the one or more multicast group members toward an upstream router.

15. A multicast optimization method in a cross-VLAN switching devices operatively coupled to one or more multicast group members associated with at least one of a plurality of VLANs and to one or more nodes via a VLAN-tagged communications link;

the method comprising the steps of;

(a) a registration processing method comprising;

(i) receiving a plurality of multicast declaration messages specifying a first multicast group identification, wherein the multicast declaration messages originate from multicast group members associated with the plurality of VLANs;

(ii) registering each of the plurality of multicast group members from which the multicast declaration messages originated; and

(iii) forwarding only the first multicast declaration message of the plurality of multicast declaration messages to an upstream router;

(b) a multicast stream processing method comprising;

(i) receiving a multicast stream having the first multicast group identification from a multicast group member associated with a first VLAN of the plurality of VLANs;

(ii) switching the multicast stream towards substantially all of the one or more multicast group members, associated with the first VLAN, that are registered to receive the multicast stream; and

(iii) distributing the multicast stream towards substantially all of the one or more multicast group members, associated with the one or more VLANs outside of the first VLAN, that are registered to receive the multicast stream;

wherein the number of duplicate multicast streams that propagate across said one or more VLAN-tagged links is minimal.

23. A cross-VLAN switching device operatively coupled to a subnet including a second node;

the switching device and node configured to support a plurality of VLANs including a first VLAN and a second VLAN, and VLAN tagging;

the cross-VLAN switching device comprising;

(a) a management module comprising one or more VLAN/multicast group membership tables for registering multicast group membership subscriptions; and

(b) a packet forwarding engine for;

(i) switching unicast packets within each of the plurality of VLANs; and

(ii) routing one or more multicast packets between the plurality of VLANs in accordance with the multicast group membership subscriptions of the one or more VLAN/multicast group membership tables;

wherein transmission of one or more duplicative multicast packets across VLAN tag-aware communications links is minimal.

24. A multicast optimization method for a packet-based network including a plurality of nodes interconnected by a plurality of links, and a multicast group, wherein the multicast group includes a first node belonging to a first VLAN and a second node belonging to a second VLAN, wherein the first VLAN and the second VLAN are different, the method comprising the steps of:

(a) receiving at a third node a packet destined for the multicast group;

(b) transmitting the packet from the third node to the first node on a first path; and

(c) transmitting the packet from the third node to the second node on a second path, wherein the first path and the second path include a common VLAN-tagged link supporting the first VLAN and the second VLAN, and wherein the packet traverses the common VLAN tagged link once.