DWDM is a core technology that is now widely used in long-haul networks, owing to its huge terabits/second link rates. Routing in DWDM networks has long been a research focus. However, most studies have only looked at single domain architectures. Nevertheless, as DWDM technology proliferates there is a critical need for multi-domain control algorithms. Namely, as the number of inter-connected networks (domains) increase, it becomes impossible for a single node to maintain information about the whole network. Needless to say, there is a pressing need for some kind of information aggregation and dissemination of this information in a constrained manner. Topology abstraction provides a way to aggregate/abstract the information pertaining to a whole domain so as to minimize the information divulged to other domains. In this work we compare different topology abstraction schemes coupled with a few wavelength assignment schemes and negotiate a trade off between blocking probability and routing overhead.