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

From: Xu Xiaohu <[email-masked]>
Date: Wed, 05 Aug 2009 16:23:11 +0800

Hi,

> I am afraid whether tracking would be possible as suggested by you.
> 
> Because you have mentioned about one source network from 
> which traffic is received.

It's just an example for illustrating the basic idea;)

> But in real scenario, there could be "n" number of source 
> networks, i.e. (S, G) entries would be available. And the 
> uplink could be down for some "S" network where as there 
> could be many active (S, G), (*, G) trees would be present.

In the case that there are more than one upstream links on the last-hop PIM
router (as DR), all of them should be tracked. If all of them down,  the PIM
router could cease the DR role.  However, in most cases, two last-hop
routers each with ONE uplink are enough for redundancy.  Note that the
uplink rent is not cheap.

> And I don’t know whether it will be a good idea to downgrade 
> ourselves to be non DR would be a good idea for these conditions.
> 
> So, my two cents would be, the VRRP (or) HSRP should have 
> tracking mechanism for specific source networks and they 
> should control these kind of scenerios.

Unfortunately no, the tracking mechanism in VRRP or HSRP is not that
intelligent as you expected. Hence, what I proposed is just the same as the
usage in VRRP, and I think this mechanism can shoot most cases.

Xiaohu

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of Xu Xiaohu
> Sent: Wednesday, August 05, 2009 12:49 PM
> To: 'Prashant Jhingran (pjhingra)'
> Cc: [email-masked]
> Subject: [pim] 答复: 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: [email-masked] [mailto:[email-masked]] On 
> Behalf Of 
> > Xu Xiaohu
> > Sent: Wednesday, August 05, 2009 9:33 AM
> > To: 'Su Haiyang'; [email-masked]
> > 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:[email-masked]]
> > > Sent: Wednesday, August 05, 2009 11:39 AM
> > > To: 'Su Haiyang'; [email-masked]
> > > 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: [email-masked] [mailto:[email-masked]]
> > On Behalf
> > > > Of Xu Xiaohu
> > > > Sent: Wednesday, August 05, 2009 11:00 AM
> > > > To: [email-masked]
> > > > 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
> > > > [email-masked]
> > > > https://www.ietf.org/mailman/listinfo/pim
> > > >
> > >
> >
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