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According to some documentation, it seems to be also 128KB. When I try, and I have a request lager than 128KB, the request isn't blocked, so that would mean that the 128KB is not the limit. The only think I can think of is that it only checks the first 128KB of data.
Your understanding here is correct Azure Front Door WAF only inspects the first 128KB of the data and the remaining data is allowed through without inspection.
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