System device and method for reducing forwarding states in a communication system

• US 6,707,796 B1
• Filed: 05/07/1999
• Issued: 03/16/2004
• Est. Priority Date: 05/07/1999
• Status: Expired due to Fees

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Li, Yunzhou
• Primary Examiner(s): HO, DUC CHI
• Application Number:
  US09/307,190
• Time in Patent Office: 1,775 Days
• Field of Search: 370/241, 370/216, 370/248, 370/242, 370/225, 370/227, 370/390, 370/400, 370/401, 370/392, 370/256, 370/252, 370/255, 370/408, 370/388, 370/351, 370/254, 709/238
• US Class Current: 370/254
• CPC Class Codes: H04L 12/185 with management of multicast group membership
• CPC Class Codes: H04L 12/1877 Measures taken prior to transmission
• CPC Class Codes: H04L 12/1881 with schedule organisation, e.g. priority, sequence management
• CPC Class Codes: H04L 45/04 Interdomain routing, e.g. hierarchical routing
• CPC Class Codes: H04L 45/16 Multipoint routing
• CPC Class Codes: H04L 45/48 Routing tree calculation
• CPC Class Codes: H04L 45/54 Organization of routing tables

Abstract

A system, device, and method for reducing forwarding states in a network domain designates a forwarding device to forward multicast packets for the (source, group) pair. A number of (source, group) pairs may be aggregated to form an aggregated (source, group) pair that is rooted at the forwarding device. For each multicast packet forwarded by the forwarding device, the forwarding device inserts an option field identifying the forwarding device. Interior devices in the network domain forward multicast packets based upon at least the forwarding device identified in the option field of the multicast packet, particularly by maintaining a list of forwarding devices in the network domain and electing a designated forwarding device from which to receive multicast packets. The interior devices forward multicast packets received from the designated forwarding device, and drop multicast packets received from other forwarding devices.

Claims

1. A method for reducing forwarding states by a device in a network domain of a communication system, the method comprising:

receiving a multicast packet for a (source,group) pair;

determining whether the device is the designated multicast source proxy device for the (source, group) pair by maintaining a list of multicast source proxy devices for the (source, group) pair and determining the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices based upon a predetermined priority scheme;

wherein each multicast source proxy device in the list of multicast source proxy devices is associated with priority information indicating a relative priority for the multicast source proxy device to be the designated multicast source proxy device wherein the priority information comprises at least one of;

a predetermined metric indicating preference value a number of device hops from the multicast source proxy device to a multicast source for the (source, group) pair; and

an Internet Protocol address for the multicast source proxy device.

2. The method of claim 1, comprising:

determining whether to accept the multicast packet,wherein the step of determining whether the device is a designated multicast source proxy device for the (source, group) pair, is performed once the multicast packet is accepted;

inserting an option field into the multicast packet, if the device is the designated multicast source proxy device for the (source, group) pair, the option field including a device identifier identifying the device; and

forwarding the multicast packet including the option field, if the device is the designated multicast source proxy device for the (source, group) pair.

3. The method of claim 2, wherein the multicast packet is an interdomain multicast packet including an option field from another routing domain, and wherein determining whether to accept the multicast packet comprises:

accepting the multicast packet and removing the option field from the multicast packet.

4. The method of claim 2, wherein the multicast packet is an interdomain multicast packet including an option field from another routing domain, and wherein determining whether to accept the multicast packet comprises:

dropping the multicast packet.

5. The method of claim 2, further comprising:

determining that the designated multicast source proxy device for the (source, group) pair has failed;

inserting the option field into the multicast packet, the option field including the device identifier identifying the device and further including an indicator indicating that the designated multicast source proxy device has failed; and

forwarding the multicast packet including the option field.

6. The method of claim 1, wherein maintaining the list of multicast source proxy devices for the (source, group) pair comprises:

maintaining an index entry for the (source, group) pair; and

maintaining a multicast source proxy entry for each multicast source proxy device.

7. The method of claim 6, wherein maintaining the list of multicast source proxy devices for the (source, group) pair comprises:

creating a multicast source proxy entry for the device.

8. The method of claim 6, wherein the multicast packet includes an option field identifying another multicast source proxy device in the network domain, and wherein maintaining the list of multicast source proxy devices for the (source, group) pair comprises:

creating a multicast source proxy entry for the other multicast source proxy device based upon the option field in the multicast packet.

9. The method of claim 1, wherein the priority information, and wherein determining the designated multicast source proxy device for the (source, group) air from among the multicast source proxy devices in the list of multicast source proxy devices comprises electing as the designated multicast source proxy device the multicast source proxy device having the highest relative priority.

10. The method of claim 9, wherein determining the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices comprises:

electing as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, if only one multicast source proxy device has the lowest metric preference value;

electing as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value and the lowest metric, if more than one multicast source proxy device has the lowest metric preference value and only one multicast source proxy device has the lowest metric; and

selecting as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, the lowest metric, and the lowest Internet Protocol address, if more than one multicast source proxy device has the lowest metric preference value and the lowest metric.

11. The method of claim 1, comprising:

receiving the multicast packet;

decapsulating the multicast packet;

decrypting the decapsulated multicast packet;

inserting the option field into the decrypted multicast packet; and

forwarding the multicast packet including the option field.

12. A device for reducing forwarding states in a network domain of a communication system, the device comprising:

receiving logic operably coupled to receive a multicast packet for a (source, group) pair;

multicast source proxy logic operably coupled to determine whether to accept the multicast packet and to insert an option field into the multicast packet if the device is a designated multicast source proxy device for the (source, group) pair, wherein the multicast source proxy logic is operably coupled to maintain a list of multicast source proxy devices for the (source, group) pair and determine the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices based upon a predetermined priority scheme, wherein the multicast source proxy logic is operably coupled to associate each multicast source proxy device in the list of multicast source proxy devices with priority information indicating a relative priority for the multicast source proxy device to be the designated multicast source proxy device, wherein the priority information comprises at least one of a predetermined metric preference value indicating a number of device hops from the multicast source proxy device to a multicast source for the (source, group) pair; and

an Internet Protocol address for the multicast source proxy device; and

forwarding logic responsive to the receiving logic and operably coupled to forward the multicast packet including the option field identifying the device.

13. The device of claim 12, comprising a border device in a routing domain.

14. The device of claim 13, comprising:

the forwarding logic operably coupled to forward the multicast packet including the option field, if the device is the designated multicast source proxy device for the (source, group) pair.

15. The device of claim 14, wherein the multicast packet is an interdomain multicast packet including an option field from another routing domain and wherein the multicast source. proxy logic is operably coupled to accept the multicast packet and remove the option field from the multicast packet.

16. The device of claim 14, wherein the multicast packet is an interdomain multicast packet including an option field from another network domain, and wherein the multicast source proxy logic is operably coupled to drop the multicast packet.

17. The device of claim 14, wherein the multicast packet is an intradomain multicast packet including an option field from another network domain, and wherein the multicast source proxy logic is operably coupled to accept the multicast packet and remove the option field from the multicast packet.

18. The device of claim 12, wherein the multicast source proxy logic is operably coupled to maintain an index entry for the (source, group) pair and a multicast source proxy entry for each multicast source proxy device.

19. The device of claim 18, wherein the multicast source proxy logic is operably coupled to create a multicast source proxy entry for the device.

20. The device of claim 18, wherein the multicast packet includes an option field identifying another multicast source proxy device in the network domain, and wherein the multicast source proxy logic is operably coupled to create a multicast source proxy entry for the other multicast source proxy device based upon the option field in the multicast packet.

21. The device of claim 12, wherein the multicast source proxy logic is operably coupled to elect as the designated multicast source proxy device the multicast source proxy device having the highest relative priority.

22. The device of claim 21, wherein the multicast source proxy logic is operably coupled to elect electing as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, if only one multicast source proxy device has the lowest metric preference value;

to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value and the lowest metric, if more than one multicast source proxy device has the lowest metric preference value and only one multicast source proxy device has the lowest metric; and

to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, the lowest metric, and the lowest Internet Protocol address, if more than one multicast source proxy device has the lowest metric preference value and the lowest metric.

23. The device of claim 12, wherein the multicast source proxy logic is operably coupled to determine that the designated multicast source proxy device for the (source, group) pair has failed and to insert the option field into the multicast packet, the option field including the device identifier identifying the device and further including an indicator indicating that the designated multicast source proxy device has failed.

24. The device of claim 12, comprising a security broker in a routing domain.

25. The device of claim 24, comprising:

the receiving logic operably coupled to receive the multicast packet;

decapsulating logic operably coupled to decapsulate the multicast packet;

decryption logic operably coupled to decrypt the decapsulated multicast packet; and

the forwarding logic operably coupled to forward the decrypted multicast packet including the option field identifying the device.

26. A program product comprising a computer readable medium having embodied therein a computer program for reducing forwarding states by a device in a network domain of a communication system, the computer program comprising:

receiving logic programmed to receive a multicast packet for a (source, group) pair, multicast source proxy logic programmed to determine whether to accept the multicast packet and to insert an option field into the multicast packet if the device is a designated multicast source proxy device for the (source, group) par;

wherein the multicast source proxy logic is programmed to maintain a list of multicast source proxy devices for the (source, group) pair and determine the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices based upon a predetermined priority scheme wherein the multicast source proxy logic is programmed to associated each multicast source proxy device in the list of multicast source proxy devices with priority information indicating a relative priority for the multicast source proxy device to be the designated multicast source proxy device, wherein the priority information comprises at least one of a predetermined metric preference value indicating a number of device hops from the multicast source proxy device to a multicast source for the (source, group) pair, and an Internet Protocol address for the multicast source proxy device, and

forwarding logic responsive to the receiving logic and programmed to forward the multicast packet including the option field identifying the device.

27. The program product of claim 26, wherein the device is a border device in a routing domain.

28. The program product of claim 27, comprising:

the forwarding logic programmed to forward the multicast packet including the option field, if the device is the designated multicast source proxy device for the (source, group) pair.

29. The program product of claim 28, wherein the multicast packet is an interdomain multicast packet including an option field from another routing domain, and wherein the multicast source proxy logic is programmed to accept the multicast packet and remove the option field from the multicast packet.

30. The program product of claim 28, wherein the multicast packet is an interdomain multicast packet including an option field from another network domain, and wherein the multicast source proxy logic is programed to drop the multicast packet.

31. The program product of claim 28, wherein the multicast packet is an intradomain multicast packet including an option field from another network domain, and wherein the multicast source proxy logic is programmed to accept the multicast packet and remove the option field from the multicast packet.

32. The program product of claim 26, wherein the multicast source proxy logic is programmed to maintain an index entry for the (source, group) pair and a multicast source proxy entry for each multicast source proxy device.

33. The program product of claim 32, wherein the multicast source proxy logic is programmed to create a multicast source proxy entry for the device.

34. The program product of claim 32, wherein the multicast packet includes an option field identifying another multicast source proxy device in the network domain, and wherein the multicast source proxy logic is programed to create a multicast source proxy entry for the other multicast source proxy device based upon the option field in the multicast packet.

35. The program product of claim 26 wherein the multicast source proxy logic is programmed to elect as the designated multicast source Proxy device the multicast source proxy device having the highest relative priority.

36. The program product of claim 35, wherein the multicast source proxy logic is programed to elect electing as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, if only one multicast source proxy device has the lowest metric preference value;

to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value and the lowest metric, if more than one multicast source proxy device has the lowest metric preference value and only one multicast source proxy device has the lowest metric; and

to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, the lowest metric, and the lowest Internet Protocol address, if more than one multicast source proxy device has the lowest metric preference value and the lowest metric.

37. The program product of claim 26, wherein the multicast source proxy logic is programmed to determine that the designated multicast source proxy device for the (source, group) pair has failed and to insert the option field into the multicast packet, the option field including the device identifier identifying the device and further including an indicator indicating that the designated multicast source proxy device has failed.

38. The program product of claim 26, wherein the device is a security broker in a routing domain.

39. The program product of claim 38, comprising:

the receiving logic programmed to receive the multicast packet;

decapsulating logic programmed to decapsulate the multicast packet;

decryption logic programmed to decrypt the decapsulated multicast packet; and

the forwarding logic programmed to forward the decrypted multicast packet including the option field identifying the device.

40. A method for reducing forwarding states by an interior device in a network domain of a communication system, the method comprising:

receiving a multicast packet for the (source, group) pair, wherein the multicast packet includes an option field identifying a border device in the routing domain, and wherein the option field further includes a source mask for the (source, group) pair;

determining whether the (source, group) pair is under multicast source proxy control; and

determining whether to accept the multicast packet based upon a designated multicast source proxy device for the (source, group) pair, if the (source, group) pair is under multicast source proxy control.

41. The method of claim 40, wherein determining whether to accept the multicast packet comprises:

determining whether the border device is the designated multicast source proxy device for the (source, group) pair.

42. The method of claim 41, wherein determining whether the border device is the designated multicast source proxy device for the (source, group) pair comprises:

maintaining a list of multicast source proxy devices for the (source, group) pair; and

determining the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices based upon a predetermined priority scheme.

43. The method of claim 42, wherein maintaining the list of multicast source proxy devices for the (source, group) pair comprises:

maintaining an index entry for the (source, group) pair; and

maintaining a multicast source proxy entry for each multicast source proxy device.

44. The method of claim 43, wherein maintaining the list of multicast source proxy devices for the (source, group) pair comprises:

creating a multicast source proxy entry for the border device.

45. The method of claim 42, wherein each multicast source proxy device in the list of multicast source proxy devices is associated with priority information indicating a relative priority for the multicast source proxy device to be the designated multicast source proxy device, and wherein determining the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices comprises electing as the designated multicast source proxy device the multicast source proxy device having the highest relative priority.

46. The method of claim 45, wherein the priority information comprises at least one of:

a predetermined metric preference value;

a predetermined metric indicating a number of device hops from the multicast source proxy device to a multicast source for the (source, group) pair; and

an Internet Protocol address for the multicast source proxy device.

47. The method of claim 46, wherein determining the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices comprises:

electing as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, if only one multicast source proxy device has the lowest metric preference value;

electing as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value and the lowest metric, if more than one multicast source proxy device has the lowest metric preference value and only one multicast source proxy device has the lowest metric; and

electing as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, the lowest metric, and the lowest Internet Protocol address, if more than one multicast source proxy device has the lowest metric preference value and the lowest metric.

48. The method of claim 42, wherein the option field further includes an indicator indicating the designated multicast source proxy device has failed, and wherein determining whether to accept the multicast packet comprises:

removing the designated multicast source proxy device from the list of multicast source proxy devices for the (source, group) pair;

determining a new designated multicast source proxy device from among the remaining multicast source proxy devices in the list of multicast source proxy devices for the (source, group) pair; and

determining whether the border device is the new designated multicast source proxy device for the (source, group) pair.

49. The method of claim 41, comprising:

receiving the multicast packet including the option field identifying the border device in the routing domain;

determining that the border device is the designated multicast source proxy device for the (source, group) pair; and

accepting the multicast packet.

50. The method of claim 41, comprising:

receiving the multicast packet including the option field identifying the border device in the routing domain;

determining that the border device is not the designated multicast source proxy device for the (source, group) pair; and

dropping the multicast packet.

51. The method of claim 40, further comprising:

maintaining a source mask for the (source, group) pair; and

updating the source mask for the (source, group) pair based upon the source mask in the option field of the multicast packet.

52. The method of claim 51, wherein updating the source mask for the (source, group) based upon the source mask in the option field of the multicast packet comprises:

setting the source mask for the (source, group) pair equal to the source mask in the option field of the multicast packet, if the source mask in the option field of the multicast packet is more specific than the source mask for the (source, group) pair.

53. The method of claim 40, wherein determining whether to accept the multicast packet comprises:

determining a metric for the interior device indicating a number of device hops from the interior device to a multicast source for the (source, group) pair;

determining the designated multicast source proxy device for the (source, group) pair;

determining a metric for the designated multicast source proxy device;

determining whether the metric for the interior device is better than the metric for the designated multicast source proxy device; and

accepting the multicast packet, if the metric for the interior device is better than the metric for the designated multicast source proxy device.

54. The method of claims 40, further comprising:

forwarding the multicast packet by the interior device, if the interior device accepts the multicast packet.

55. A device for reducing forwarding states in a network domain of a communication system, the device comprising:

receiving logic operably coupled to receive a multicast packet for a (source, group) pair, wherein the multicast packet includes an option field identifying a border device in the network domain and wherein the option field further includes a source mask for the (source, group) pair; and

multicast source proxy logic operably coupled to determine whether to accept the multicast packet based upon a designated multicast source proxy device for the (source, group) pair.

56. The device of claim 55, wherein the multicast source proxy logic is operably coupled to determine whether the border device is the designated multicast source proxy device for the (source, group) pair.

57. The device of claim 56, wherein the multicast source proxy logic is operably coupled to maintain a list of multicast source proxy devices for the (source, group) pair and determine the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices based upon a predetermined priority scheme.

58. The device of claim 57, wherein the multicast source proxy logic is operably coupled to maintain an index entry for the (source, group) pair and a multicast source proxy entry for each multicast source proxy device.

59. The device of claim 58, wherein the multicast source proxy logic is operably coupled to create a multicast source proxy entry for the border device.

60. The device of claim 57, wherein the multicast source proxy logic is operably coupled to associated each multicast source proxy device in the list of multicast source proxy devices with priority information indicating a relative priority for the multicast source proxy device to be the designated multicast source proxy device, and wherein the multicast source proxy logic is operably coupled to elect as the designated multicast source proxy device the multicast source proxy device having the highest relative priority.

61. The device of claim 60, wherein the priority information comprises at least one of:

a predetermined metric preference value;

a predetermined metric indicating a number of device hops from the multicast source proxy device to a multicast source for the (source, group) pair; and

an Internet Protocol address for the multicast source proxy device.

62. The device of claim 61, wherein the multicast source proxy logic is operably coupled to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, if only one multicast source proxy device has the lowest metric preference value;

to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value and the lowest metric, if more than one multicast source proxy device has the lowest metric preference value and only one multicast source proxy device has the lowest metric; and

to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, the lowest metric, and the lowest Internet Protocol address, if more than one multicast source proxy device has the lowest metric preference value and the lowest metric.

63. The device of claim 57, wherein the option field further includes an indicator indicating the designated multicast source proxy device has failed, and wherein the multicast source proxy logic is operably coupled to remove the designated multicast source proxy device from the list of multicast source proxy devices for the (source, group) pair, determine a new designated multicast source proxy device from among the remaining multicast source proxy devices in the list of multicast source proxy devices for the (source, group) pair, and determine whether the border device is the new designated multicast source proxy device for the (source, group) pair.

64. The device of claim 56, wherein the multicast source proxy logic is operably coupled to accept the multicast packet if the border device is the designated multicast source proxy device for the (source, group) pair.

65. The device of claim 56, wherein the multicast source proxy logic is operably coupled to drop the multicast packet if the border device is not the designated multicast source proxy device for the (source, group) pair.

66. The device of claim 55, wherein the multicast source proxy logic is operably coupled to maintain a source mask for the (source, group) pair and update the source mask for the (source, group) pair based upon the source mask in the option field of the multicast packet.

67. The device of claim 66, wherein the multicast source proxy logic is operably coupled to set the source mask for the (source, group) pair equal to the source mask in the option field of the multicast packet, if the source mask in the option field of the multicast packet is more specific than the source mask for the (source, group) pair.

68. The device of claim 55, wherein the multicast source proxy logic is operably coupled to determine a metric for the interior device indicating a number of device hops from the interior device to a multicast source for the (source, group) pair and to accept the multicast packet if the metric for the interior device is better than a metric for the designated multicast source proxy device.

69. The device of claim 55, further comprising:

forwarding logic responsive to the multicast source proxy logic and operably coupled to forward the multicast packet, if the interior device accepts the multicast packet.

70. A program product comprising a computer readable medium having embodied therein a computer program for reducing forwarding states by an interior device in a network domain of a communication system, the computer program comprising:

receiving logic programed to receive a multicast packet for a (source, group) pair, wherein the multicast packet includes an option field identifying a border device in the network domain and wherein the option field further includes a source mask for the (source, group) pair; and

multicast source proxy logic programmed to determine whether to accept the multicast packet based upon a designated multicast source proxy device for the (source, group) pair.

71. The program product of claim 70, wherein the multicast source proxy logic is programmed to determine whether the border device is the designated multicast source proxy device for the (source, group) pair.

72. The program product of claim 71, wherein the multicast source proxy logic is programmed to maintain a list of multicast source proxy devices for the (source, group) pair and determine the designated multicast source proxy device for the (source, group) pair from among the multicast source proxy devices in the list of multicast source proxy devices based upon a predetermined priority scheme.

73. The program product of claim 72, wherein the multicast source proxy logic is programmed to maintain an index entry for the (source, group) pair and a multicast source proxy entry for each multicast source proxy device.

74. The program product of claim 73, wherein the multicast source proxy logic is programmed to create a multicast source proxy entry for the border device.

75. The program product of claim 72, wherein the multicast source proxy logic is programmed to associated each multicast source proxy device in the list of multicast source proxy devices with priority information indicating a relative priority for the multicast source proxy device to be the designated multicast source proxy device, and wherein the multicast source proxy logic is programmed to elect as the designated multicast source proxy device the multicast source proxy device having the highest relative priority.

76. The program product of claim 75, wherein the priority information comprises at least one of:

a predetermined metric preference value;

a predetermined metric indicating a number of device hops from the multicast source proxy device to a multicast source for the (source, group) pair; and

a Internet Protocol address for the multicast source proxy device.

77. The program product of claim 76, wherein the multicast source proxy logic is programmed to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, if only one multicast source proxy device has the lowest metric preference value;

to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value and the lowest metric, if more than one multicast source proxy device has the lowest metric preference value and only one multicast source proxy device has the lowest metric; and

to elect as the designated multicast source proxy device the multicast source proxy device having the lowest metric preference value, the lowest metric, and the lowest Internet Protocol address, if more than one multicast source proxy device has the lowest metric preference value and the lowest metric.

78. The program product of claim 72, wherein the option field further includes an indicator indicating the designated multicast source proxy device has failed, and wherein the multicast source proxy logic is programmed to remove the designated multicast source proxy device from the list of multicast source proxy devices for the (source, group) pair, determine a new designated multicast source proxy device from among the remaining multicast source proxy devices in the list of multicast source proxy devices for the (source, group) pair, and determine whether the border device is the new designated multicast source proxy device for the (source, group) pair.

79. The program product of claim 71, wherein the multicast source proxy logic is programmed to accept the multicast packet if the border device is the designated multicast source proxy device for the (source, group) pair.

80. The program product of claim 71, wherein the multicast source proxy logic is programmed to drop the multicast packet if the border device is not the designated multicast source proxy device for the (source, group) pair.

81. The program product of claim 70, wherein the multicast source proxy logic is programmed to maintain a source mask for the (source, group) pair and update the source mask for the (source, group) pair based upon the source mask in the option, field of the multicast packet.

82. The program product of claim 81, wherein the multicast source proxy logic is programmed to set the source mask for the (source, group) pair equal to the source mask in the option field of the multicast packet, if the source mask in the option field of the multicast packet is more specific than the source mask for the (source, group) pair.

83. The program product of claim 70, wherein the multicast source proxy logic is programmed to determine a metric for the interior device indicating a number of device hops from the interior device to a multicast source for the (source, group) pair and to accept the multicast packet if the metric for the interior device is better than a metric for the designated multicast source proxy device.

84. The program product of claim 70, further comprising:

forwarding logic responsive to the multicast source proxy logic and programmed to forward the multicast packet, if the interior device accepts the multicast packet.

85. A communication system comprising at least one forwarding device in communication with a number of interior devices, wherein the forwarding device forwards a multicast packet for a (source, group) pair, the multicast packet including an option field identifying the forwarding device and including a source mask for the (source, group) pair, and wherein each interior device forwards the multicast packet based upon at least the forwarding device identified in the option field of the multicast packet.

86. The communication system of claim 85;

wherein each interior device determines a designated forwarding device from among the at least one forwarding device in the network domain and forwards the multicast packet if the forwarding device identified in the option field of the multicast packet is the designated forwarding device.