Kestrel generates the request ID as {ConnectionId}:{Request number}. The connection id is the base32 encoded version of a long using the alphabet 1-9, and A – V. The request count is the number of requests over that connection. The nth request over a specific connection is {ConnectionId}:{n}
https://github.com/aspnet/KestrelHttpServer/blob/a48222378b8249a26b093b5b835001c7c7b45815/src/Kestrel.Core/Internal/Infrastructure/CorrelationIdGenerator.cs
https://github.com/aspnet/KestrelHttpServer/blob/0aff4a0440c2f393c0b98e9046a8e66e30a56cb0/src/Kestrel.Core/Internal/Http/Http1Connection.cs#L446