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

[Su Haiyang <suhaiyang at huawei.com>]

Hi,
  PIM is designed as a protocol independent multicast. The route to
source/RP PIM depend on is up to IGP, not it self. 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, so that PIM would also
try to establish a new multicast tree by sending a new PIM join to the
non-DR router through that LAN transit network.

Regards
Su Haiyang

-----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
> 
> 
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