Multicast high availability enhancements for faster convergence
View Patent ↗During initial formation of an adjacency, two neighboring PIM speakers exchange, in their hello messages, information as to whether each supports a non-stop forwarding (NSF) capability. When one of the PIM speakers restarts, the PIM neighbor senses this event, and responds by immediately forwarding its entire relevant Tree Information Base (TIB) to the restarting PIM speaker, followed by an End Of TIB (EOTIB) marker. Once the restarting PIM speaker has received TIB contents and EOTIB markers from each of its PIM neighbors, it can immediately finalize its multicast routes. In a group of routers participating in this non-stop forwarding capability, it may be possible to significantly reduce the configuration delay time currently required before purging stale multicast entries from the line card forwarding tables. Other embodiments are also described and claimed.
1. A method for operating a first router, the method comprising:
in response to a condition forcing a restart of an IP multicast speaker role for the first router, indicating the restart condition to a first multicast neighbor router by advertising a first IP multicast speaker generation identifier to the first multicast neighbor router prior to the restart, and advertising a second IP multicast speaker generation identifier to the first multicast neighbor router subsequent to the restart;
receiving IP multicast tree information from the first multicast neighbor router;
building internal router path IP multicast forwarding information from the received IP multicast tree information;
receiving an end-of-tree marker from the first multicast neighbor router indicating that the neighbor router has completed transmission of the IP multicast tree information to the first router; and
in response to receiving the end-of-tree marker, activating the internal router path IP multicast forwarding information for data path forwarding within the first router.
2. The method of claim 1 , wherein the first multicast neighbor router is one of a plurality of multicast neighbor routers to the first router, the first router indicating the restart condition to each multicast neighbor router in the plurality, the first router receiving the IP multicast tree information and the end-of-tree markers from each multicast neighbor router in the plurality, the first router activating the internal router path IP multicast forwarding information in response to receipt of the end-of-tree marker from each multicast neighbor router in the plurality.
3. The method of claim 2 , wherein when the first router fails to receive end-of-tree markers from every multicast neighbor router in the plurality, the first router activates the internal router path IP multicast forwarding information after the expiry of a configuration timer.
4. The method of claim 2 , further comprising operating a minimum configuration timer, and wherein when the first router receives end-of-tree markers from each multicast neighbor router in the plurality prior to expiry of the minimum configuration timer, waiting for the expiry of the minimum configuration timer before activating the internal router path IP multicast forwarding information.
5. The method of claim 4 , further comprising receiving an IP multicast join request from at least one local-area-network-connected multicast receiver prior to the expiry of the minimum configuration timer, the first router incorporating the IP multicast join request into the internal router path IP multicast forwarding information that is activated.
6. The method of claim 1 , further comprising the first router caching prior internal router path IP multicast forwarding information as that information existed at a point in time prior to restart of the IP multicast speaker role, the first router, when building internal router path IP multicast forwarding information from the received IP multicast tree information, referencing the cached prior internal router path IP multicast forwarding information and attempting to build the new internal router path IP multicast forwarding information consistent with the cached prior internal router path IP multicast forwarding information.
7. The method of claim 6 , wherein, when an entry in the built internal router path IP multicast forwarding information pertains to a IP multicast path that is not contained in the cached internal router path IP multicast forwarding information, the first router activates the entry without waiting for receipt of the end-of-tree marker.
8. The method of claim 1 , wherein the end-of-tree marker comprises an empty IP multicast join/prune message.
9. The method of claim 1 , further comprising advertising to the first multicast neighbor router a capability to process the end-of-tree marker.
10. A method for operating a first router, the method comprising:
maintaining an IP multicast tree information base;
detecting a restart condition of a multicast neighbor router, wherein detecting a restart condition comprises saving a generation identifier transmitted by the multicast neighbor router, comparing the saved generation identifier to a subsequently received generation identifier, and declaring a restart condition when the saved and subsequently received generation identifiers differ;
in response to detecting the restart condition, transmitting to the multicast neighbor router all IP multicast tree information in the IP multicast tree information base that is needed by the multicast neighbor router; and
transmitting, to the multicast neighbor router, an end-of-tree marker to indicate that all IP multicast tree information needed by the multicast neighbor router has been transmitted.
11. The method of claim 10 , wherein detecting a restart condition using generation identifiers is only performed when the multicast neighbor router has previously indicated that it is capable of processing end-of-tree markers.
12. The method of claim 10 , wherein detecting a restart condition comprises timing out the multicast neighbor router as an IP multicast speaker, maintaining information identifying the multicast neighbor router as a timed-out IP multicast speaker, and upon receiving a subsequent IP multicast control packet from the multicast neighbor router, declaring a restart.
13. The method of claim 10 , wherein the end-of-tree marker comprises an empty IP multicast join/prune message.
14. An apparatus comprising a computer memory containing instructions that, when executed by a processor or group of processors in a first router, cause the first router to perform a method comprising:
in response to a condition forcing a restart of an IP multicast speaker role for the first router, indicating the restart condition to a first multicast neighbor router, wherein indicating a restart condition comprises advertising a first IP multicast speaker generation identifier to the first multicast neighbor router prior to the restart, and advertising a second IP multicast speaker generation identifier to the second multicast neighbor router subsequent to the restart;
receiving IP multicast tree information from the first multicast neighbor router;
building internal router path IP multicast forwarding information from the received IP multicast tree information.
15. The apparatus of claim 14 , wherein the first multicast neighbor router is one of a plurality of multicast neighbor routers to the first router, the first router indicating the restart condition to each multicast neighbor router in the plurality, the first router receiving IP multicast tree information and end-of-tree markers from each multicast neighbor router in the plurality, the first router activating the internal router path IP multicast forwarding information in response to receipt of the end-of-tree marker from each multicast neighbor router in the plurality.
16. The apparatus of claim 15 , wherein when the first router fails to receive end-of-tree markers from every multicast neighbor router in the plurality, the first router activates the internal router path IP multicast forwarding information after the expiry of a configuration timer.
17. The apparatus of claim 15 , the method further comprising operating a minimum configuration timer, and wherein when the first router receives end-of-tree markers from each multicast neighbor router in the plurality prior to expiry of the minimum configuration timer, waiting for the expiry of the minimum configuration timer before activating the internal router path IP multicast forwarding information.