Originally Posted by
cygnus
I honestly would only doing such a trip on different tickets if I had several hours at CDG for changing planes. If you are on a different airline you *will* have to pick up your luggage, go through customs, change terminals, and check in again. If, e.g., you change from terminal 1 to terminal 2 I would plan on this taking at least 1.5h in case nothing(!) goes wrong. Plan at least another couple of hours in case your flight arrives late and things like that.
Personally, I would not risk it and only use two separate tickets if I had a couple of days in Paris before and after the Istanbul flights.
I read the OP as having:
IAD->(CDG connection)->IST on ST
IST->(CDG connection)->IAD in ST
And
IST->CDG->IST on whatever
So the CDG connections are on a single ticket, all on ST. So not as bad as some think.
The connection to worry about is IST (particularly comming home) where they will switch paper and perhaps airlines. That one needs a lot of padding.
To the OP, this is a completely legit nested ticket, so you can do it all on ST if desired. All you are doing is buying A->B->A with B->C->B inside of that. The connection in CDG means nothing (as long as you don't try something as dumb as missing the next leg).