[i2rs] Additional Next Hop Type in Section 2.4 of draft-ietf-i2rs-rib-data-model, et al...

"Russ White" <7riw77@gmail.com> Sun, 02 October 2016 02:59 UTC

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From: "Russ White" <7riw77@gmail.com>
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Date: Sat, 1 Oct 2016 22:59:54 -0400
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Subject: [i2rs] Additional Next Hop Type in Section 2.4 of draft-ietf-i2rs-rib-data-model, et al...
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Y'all -- 

I would like to suggest we add one more next hop type in section 2.4 of
draft-ietf-i2rs-rib-data-model, and sections 2.4 & 7.2 of
draft-ietf-i2rs-rib-info-model to include a nexthop type that tells the
forwarding device to not use a particular next hop without sending traffic
to dev/null. The specific case is this -- assume I have an ECMP group with
32 or 64 entries. In this group, I want to pin one flow to a particular set
of links, while making certain some other set of flows do _not_ use those
links. The only way to accomplish this today would be to replace every route
with the same ECMP group to provide a different set of next hops for each
one. It would be cleaner to have a construction that says, "take this next
hop out of all ECMP groups, so it is only used when specified by this
client," or some such.

Maybe something like this in section 7.2 of the rib data model might work --

7.4. Remove from ECMP next hop

If the a particular route is marked "remove from ECMP," then any routes
which recurse onto this next hop as part of an ECMP group will remove any
paths using this route as a next hop from the ECMP group. This allows the
I2RS controller to remove ECMP traffic from a particular next hop to attain
finer grained control over the use of specific links to which particular
elephant flows may be pinned, or which may be otherwise congested, etc.

I don't know of any implementation that could do this right now, but this
seems like a useful addition to the set of available next hops (?).