Hi Linda, > Is it correct that the intent of the draft is to prevent some “elephant > flows” from being placed over certain links?
I would phrase it somewhat differently. One of the goals of the draft is to allow network operators to define a minimum bandwidth threshold for a FlexAlgo topology. If you know that you have 200Gb/s flows, then you might well want to ensure that they are placed on 400Gb/s links (or greater). You would then route your ‘elephant flows’ on your ‘elephant topology’. Another goal is to allow operators to cause SPF to follow a metric other than the best-effort or TE metric. One application might well be to assign metrics based on bandwidth, causing flows to travel along the highest bandwidth paths. We are not proposing changing SPF, so it will still optimize for the cumulative metric to the destination, so the result will be the lowest cumulative metric, which is not necessarily just the absolute maximum of link bandwidths. > Section 2.1 listed the TLV for the ISIS Generic Metric > > Is the property of preventing some flows being placed on a link to be encoded > in the Value field of the ISIS Generic Metric in Section 2.1? No. Constraints on the topology are done with the “Exclude Minimum Bandwidth” and “Maximum Delay” TLVs and are orthogonal to the metric. > Why not directly included in the value field of Flex Algo TLV? I’m not sure I understand the question, forgive me if this doesn’t address your question. Metrics need to attached to links. Thus, they need to be advertised as part of the ASLA TLV. Constraints on the topology are part of the description of the algorithm itself and belong to the FlexAlgo Definition TLV. > Section 2.3 says that using FAPM sub-TLV to indicate Flex Algo needs to use > the Generic Metric. But this property of preventing some flows to be placed > on certain links doesn’t need to be generic, does it? Again, they are orthgonal. The generic metric may be used with a leaked prefix by carrying it in the FAPM. This does NOT constrain the topology. > How does an IGP node know which link to advertise this property? Is it by > configuration? The IGP would know to advertise topology constraints for an algorithm by administrative configuration. Link attributes are also typically configured on a per-link basis and advertised by the IGP. Tony
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