zebra: Attempt to explain the rnh tracking code better #15586
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I got asked today what was going on in the rnh code. I had to take time off of what I was doing and rewrap my head around this code, since it's been a long time. As that this question may come up again in the future I am trying to document this better so that someone coming behind us will be able to read this and get a better idea of what the algorithm is attempting to do. Signed-off-by: Donald Sharp <sharpd@nvidia.com>
| * rnh 1.1.3.4 | ||
| * rnh 4.5.6.7 | ||
| * Now imagine that you have in the tree these | ||
| * prefix's: |
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"prefix's" -> "prefixes" ?
| * 1.1.1.1/32 | ||
| * 1.1.1.0/24 | ||
| * 1.1.0.0/16 | ||
| * 0.0.0.0/0 |
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might be a bit clearer if this list were reversed, so that the default, all-zeroes, prefix would be at the "top", and the /32 would be at the bottom?
| * This function would start at the 1.1.1.1/32 node, | ||
| * perform a LPM and settle on the 1.1.1.0/24 node | ||
| * as where it belongs. The code would update appropriate | ||
| * interested parties and additionally also mark the sequence |
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the discussion about the sequence number wasn't clear to me?
so if 1.1.1.2/32 is being deleted, and there's a 1.1.1.2 rnh, the rnh needs to be moved to some other (valid) prefix. the text "it would get to the 1.1.1.0/24 node and since the seqno matches we would know that it is not necessary to reconsider this node" was what confused me: the sequence number is on the rnh, not the prefix, not the "node". it might be clearer to say something like "seeing a matching sequence number on the 1.1.1.2 rnh, we know it's not necessary to reconsider the rnh."
I got asked today what was going on in the rnh code. I had to take time off of what I was doing and rewrap my head around this code, since it's been a long time. As that this question may come up again in the future I am trying to document this better so that someone coming behind us will be able to read this and get a better idea of what the algorithm is attempting
to do.