[c-nsp] How does multicast multipath next-hop-based hashingactually work?

[Arie Vayner (avayner)]

John,

In general the hash is done based on the source address (called S-Hash)
There are enhancements to be able to base the hash on S and G (called
S-G-Hash) or also taking the next hop into consideration...

Take a look here:
http://www.cisco.com/en/US/docs/ios/12_4t/ip_mcast/configuration/guide/m
ctlsplt.html

Some platforms still have it on the roadmap, so could be not yet
available...

Arie


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of John Neiberger
Sent: Thursday, October 21, 2010 21:08
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] How does multicast multipath next-hop-based
hashingactually work?

We've been having a bear of a time trying to get equitable
distributions of traffic over sets of links where the traffic is
nearly 100% multicast. We seem to end up with a couple of links that
have a lot of S,Gs attached to them and other links that only have a
few. Since the traffic rate per stream is about the same, this leads
to a lot higher utilization on certain links, and in some cases (like
at 5:00 AM this morning) one link getting overdriven to the point of
dropping production video traffic.

We've read the documentation on CCO about multicast multipath, but it
doesn't go into enough detail about how the hash works under the hood.
We need to understand this in order to engineer a workable (and
understandable) solution for this issue.

Do any of you know the details?

Thanks,
John
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