Re: [pim] 答复: DR priority adjustment automatically according to the status of the tracked interfaces

["Prashant Jhingran (pjhingra)" <pjhingra at cisco.com>]

Hi,

PIM-SM RFC takes care of such scenarios, following explains the same:

- Once the uplink on R1 goes down, R1's next-hop towards source would be via R2. IGP convergence would take care of this.
- R1 should continue to act as DR as before, however the SG/*G upstream interface would change as interface towards R2 (i.e. LAN interface)
- R2 should add interface towards R1 as OIF while IIF as upstream towards source (PIM-SM network)
- On R1 oiflist = oiflist (-) iif so although R1 would receive data traffic from R2, router R1 would not be sending it back on LAN interface
  => Hence Assert like condition would not arise.
=> However, client would continue to receive mcast data as before (it doesn't care which router is DR and who is fwd to it etc), and hence nothing to worry ! 

Hope this clarifies your doubt.

Regards,
Prashant Jhingran
www.cisco.com 
Phone:   +91-80-442 61800
 
-----Original Message-----
From: pim-bounces at ietf.org [mailto:pim-bounces at ietf.org] On Behalf Of Xu Xiaohu
Sent: Wednesday, August 05, 2009 9:33 AM
To: 'Su Haiyang'; pim at ietf.org
Subject: [pim] 答复: DR priority adjustment automatically according to the status of the tracked interfaces


>   PIM is designed as a protocol independent multicast. The route to 
> source/RP PIM depend on is up to IGP, not it self.

Yes, PIM is Protocol Independent Multicast. However, it is not a ROUTE indepedent multicast protocol.

> Just like the topology you give, the LAN is a backup transit network 
> to DR's up link. Why IGP doesn't converge through LAN to reach RP or 
> Source,

I gather you are not much falimiar with the real network configuration. Why don't you ask why we need VRRP or HSRP?

Xiaohu

> -----Original Message-----
> From: Xu Xiaohu [mailto:xuxh at huawei.com]
> Sent: Wednesday, August 05, 2009 11:39 AM
> To: 'Su Haiyang'; pim at ietf.org
> Subject: 答复: [pim] DR priority adjustment automatically according to 
> the status of the tracked interfaces
> 
> 
> >   I don't think that it is necessary for a DR to track it's upstream 
> > link to a source or RP, since IGP would care it for PIM. When a 
> > router's link to a source or RP is down, IGP would converge to 
> > another link to reach the source or RP. If there is no other link to 
> > source or RP, IGP may be fail to find a new route.
> 
> If all uplinks are down, what do you want the DR to do next?
> 
> > But isn't that be a poor topology?
> 
> Poor topology?  Two routers, each with a uplink to the Internet, are 
> used on a LAN for redundancy. Not enough?
> 
> Or do you even believe the tracking mechanism used in VRRP or HSRP is 
> useless?
> 
> Xiaohu
> 
> > -----Original Message-----
> > From: pim-bounces at ietf.org [mailto:pim-bounces at ietf.org] On Behalf 
> > Of Xu Xiaohu
> > Sent: Wednesday, August 05, 2009 11:00 AM
> > To: pim at ietf.org
> > Subject: [pim] DR priority adjustment automatically according to the 
> > status of the tracked interfaces
> > 
> > Hi all,
> > 
> > In the following PIM-SM (or SSM) scenario, R!, R2 and Client are 
> > located with the same LAN. R1 is elected as the DR for that LAN. Now 
> > R1's uplink to the PIM-SM Network  is down, as long as R1 still acts 
> > as the DR, the multicast stream will be broken soon or later.
> > 
> >              |
> >              |   +-----+    +------------------+
> >              +---+ R1  +----+                  |
> >              |   +-----+    |                  |
> >  +-------+   |              |                  |  +-------+
> >  |Client +---+              | PIM-SM Network   +--+Source |
> >  +-------+   |              |                  |  +-------+
> >              |   +-----+    |                  |
> >              +---+ R2  +----+                  |
> >              |   +-----+    +------------------+
> >              |
> > 
> > I wonder whether it is suitable for the DR (e.g., R1 in the above 
> > figure) to track the upstream link, and once the tracked link is 
> > down, its DR priority is reduced automatically so as to cease the DR 
> > role. Of couse, this mechanism is also suitable for the scenario 
> > where the Multicast Souce is connected to more than one PIM routers 
> > via LAN.
> > 
> > Any comment? Or whether some vendor has already implement this 
> > feature?
> > 
> > Xiaohu
> > 
> > 
> > _______________________________________________
> > pim mailing list
> > pim at ietf.org
> > https://www.ietf.org/mailman/listinfo/pim
> > 
> 

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