Failure tolerance in ACI

[jwendling]

I have a question about the failure tolerance in ACI.

My setup are 3 leafs and 2 spines. Usually its ok if one link is dead because the leaf would use the other spine.

Attached to this discussion is an example that shows two endpoints which are trying to communicate but Leaf1 has no connection to Spine1 and Leaf3 has no connection to Spine2. So there is no 1-hop connection possible between the endpoints. Is it possible to use a leaf switch as a bridge for the spines like in the attached image?

Example:

(red links have failure and cannot be used)

thanks for the comments,

jan

[RedNectar · Accepted solution]

Firstly, thanks for the great diagram.

ACI will handle above scenario perfectly well, because IS-IS is running in the core, Leaf1 will still see it has a path to Leaf 3 via Spine2. Spine2 will see from its IS-IS routing table that it can deliver packets to Leaf3 via Leaf2, Leaf2 knows it can get to Leaf3 via Spine1 and Spine1 has a direct connection to Leaf3.

Clearly, performance is going to be degraded, but as far as the Failure Tolerance is concerned, there is no packet delivery failure so long as the amount of traffic can be sustained.

Some things in ACI are beautiful by their simplicity.  This is one of them.

RedNectar

aka Chris Welsh

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