04-30-2009 09:26 AM - edited 03-04-2019 04:35 AM
Hi
I want to discuss a scenario.
lets say I have 2 paths to Mcast source or RP and I don't enable pim on the lower cost path,would my Mcast will work or it will not due to RPF failure.
04-30-2009 10:10 AM
Hello Mohammad,
multicast packets should be dropped for RPF check failure.
You can have troubles also with equal path costs because unicast routing support them but RPF elects only one link as the best one (no parallel links support)
Hope to help
Giuseppe
04-30-2009 10:59 AM
Hi Giuseppe
Ya with equal path costs it will select the RPF interface with higher ip address to the neigbor.
My concern was if we don;t enable pim on lower cost path and enable pim on higher cost path,it should not work due to RPF check.Just brainstorming:)Thats why pim shouild be enabled on all interfaces to avoid RPF check failures.
04-30-2009 11:00 AM
Moreover we can use tunnel to use both the links with ip mroute.
04-30-2009 11:08 AM
Hello Mohammad,
yes the GRE tunnel is the classic solution for two equal cost paths with pim not enabled on physical links.
In your original scenario it should be enough to enable pim on the unicast best path if possible.
The higher cost path will be used when the primary path fails
Hope to help
Giuseppe
04-30-2009 11:42 AM
Hi Giuseppe
The higher cost path will be used when the primary path fails
only in case if i enable pim as well on higher cost path.
04-30-2009 08:46 PM
Giuseppe,
Just to add that ss far as the equal cost past scenario is concerned, you could enable "ip multicast multipath" to get load splitting across these multiple paths.
Regards
05-01-2009 12:46 AM
Hello Harold,
thanks for this useful information.
I see this is not quite new and it is given in global configuration mode.
http://www.cisco.com/en/US/docs/ios/ipmulti/command/reference/imc_03.html#wp1015944
It is still a flow based load balancing using S,G or S,G and ip next-hop to decide which link to use.
We can say it emulates unicast CEF load balancing and allows to relax the RPF check on equal cost paths.
Best Regards
Giuseppe
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