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Re: [pim] Some thoughts on draft-mirsky-pim-bfd-p2mp-use-case

"Mankamana Mishra (mankamis)" <mankamis@cisco.com> Fri, 22 June 2018 16:00 UTC

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From: "Mankamana Mishra (mankamis)" <mankamis@cisco.com>
To: Stig Venaas <stig@venaas.com>
CC: "pim@ietf.org" <pim@ietf.org>, "draft-mirsky-pim-bfd-p2mp-use-case@ietf.org" <draft-mirsky-pim-bfd-p2mp-use-case@ietf.org>
Thread-Topic: [pim] Some thoughts on draft-mirsky-pim-bfd-p2mp-use-case
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Date: Fri, 22 Jun 2018 16:00:09 +0000
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Subject: Re: [pim] Some thoughts on draft-mirsky-pim-bfd-p2mp-use-case
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Hi Stig
In general should we not only be concerned about DR and BDR ? Even if link failure happens for non DR/BDR PIM routers, with respect to multicast we do not need to take any action. But yes, we would have increase the scope of this document to cover cases where DR load balancing is applied and we want to use BFD protection for all of the DR in shared LAN. 

Mankamana  

> On Jun 21, 2018, at 1:44 PM, Stig Venaas <stig@venaas.com> wrote:
> 
> Hi
> 
> Posting as a WG participant.
> 
> This looks useful to me and I believe it would scale better than the
> current use of p2p BFD for pim. Below are some questions I have.
> 
> Unidirectional link failures
> I believe in pim we assume that if a link fails in one direction, it
> also fails in the other direction. Several things could go wrong
> otherwise. Is it sufficient to use BFD for discovering unidirectional
> failures? p2mp BFD seems to be only in one direction normally.
> However, if we need bidirectional, is it useful to have the head query
> the tails and see if it gets responses from all neighbors? What should
> be the behavior if a failure is detected? E.g. if a link is
> partitioned (in both directions), it is beneficial to have a DR in
> each partition.
> 
> BFD only for DR?
> The draft currently assumes that it is only needed for the DR. Do we
> in pim need to detect other neighbors going down? I believe there are
> such cases. Even if one uses p2mp BFD for all pim routers, I believe
> it will scale better than the current full p2p mesh.
> 
> Stig
> 
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