Block db access by IP and username

long time no checking this list. I have a security question. I need to block access to db by IP and username, let's say that I need that user XXXX can connect ONLY from IP aaa.bbb.ccc.ddd, that is, if user XXXX wants to connect from another IP, access will be denied.  

I was thinking about using an after logon trigger to detect username and IP and kill session if it doest fit with required values, but I think this is a little bit rude. The other option I verified was using sqlnet.ora configuration but this only filters by IP and I would have to add all posssible IP's but doesnt filter users, and this is not what I need.  

Any ideas?  

TIA
Gabriel

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