Wasn't sure what to title this, so I hope I didn't confuse anybody... Also, this has probably been discussed before, but I'm new here and didn't find any information about this right off-hand.

Basically, if you want to get yourself into a position where you're opening for a nationally touring artist, who do you contact? Do you touch base with the manger/agent of the touring artist, or do you contact the booking agent for the venue?

Sorry if it's a dumb question, it just seems like I've heard it both ways before.

To clarify: I'm not talking about joining a tour, I'm talking about opening up for the particular band for one or two shows when they're performing at a venue in close proximity.
Depends on the act and how they do things. Many national touring acts travel with their own support. In that case you would need to get in touch with the promoters and agents long before hand, to see if they would allow you to open up on a particular date. Your going to have to sell yourselves to them. They want someone who can benefit the tour and headliner and have a strong local draw.

Then there are some, we'll say smaller touring acts, that will just headline a show, and there will be local support acts. In this case, get in touch with the venue, hopefully you've played there before. If you have a big enough draw and have played there before, and your a good fit to support the headliner; they may just call you. You can always get in touch with the band as well, they'll have some leeway in saying we want so and so to open up for us in X city.
Thanks! That's kind of what I thought, just wanted to check in and see what other people with possibly more experience would have to say.