I read this short stories collection about 10 years ago. All I remember about the collection is that the title of each story is the name of a currently existing city, one of which is Hanoi. If I recall correctly, each of the city is in various stages of decay or something like that. I think the collection was relatively new at the time, so it must have been published in the 90s or 00s.
I found it after a bit of sleuthing, it's The Colected Short Fiction of C. J. Cherryh.
Sunfall is a collection of stories set in the far future on an ancient Earth under a dying Sun that is emitting dangerous levels of radiation. Each story deals with a city and how it has evolved to cope with the fading Sun. Paris and New York City have become single self-contained structures with no "outside". In "The Only Death in the City (Paris)" this closed biosphere has resulted in no "new births": everyone who dies is reincarnated again in the city with all the memories of their previous lives. In "Nightgame (Rome)" the nobles while away their boredom by dreaming dreams captured from less fortunates using an apparatus no one knows the origin of.
On the other hand there wasn't any story about Hanoi. I was pretty sure about that but hey.