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

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

You have a valid point but I would say network configuration/design should take care of this.  In absence of a dynamic mechanism (IGP), perhaps a failover static route might be good enough. 
 
Regards,
Prashant Jhingran
 www.cisco.com
Phone:   +91-80-442 61800
 
-----Original Message-----
From: Xu Xiaohu [mailto:xuxh at huawei.com] 
Sent: Wednesday, August 05, 2009 12:49 PM
To: Prashant Jhingran (pjhingra)
Cc: 'Su Haiyang'; pim at ietf.org
Subject: 答复: [pim] 答复: DR priority adjustment automatically according to the status of the tracked interfaces


> 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 !

However, in most cases, there is no IGP running between R1 and R2 via the shared edge LAN. Even though IGP is ran, the interface is usually set to silent mode interface due to many reasons, e.g.  the routing security consideration, routing information flooding avoidance. Besides, for some small-scale edge site networks (e.g. only a LAN), static route, other than IGP is usually used.

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 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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