R: Combining dataset and lookup-table to extract value to new colume

I want to combine to dataframes, df1 with 15.000 obs and df2 consisting of 2.3 mill. I'm trying to match values, if df1$col1 == df2$c1, AND df1$col2 == df2$c2, then insert value from df2$dummy, to df1$col3. If no match in both, do nothing. All are 8 digits, except df2$dummy, which is a dummy of 0 or 1.

df1  col1       col2      col3
1    25382701   65352617  -
2    22363658   45363783  -
3    20019696   23274747  -

df2  c1         c2        dummy
1    17472802   65548585  1
2    20383829   24747473  0
3    20019696   23274747  0 
4    01382947   21930283  1
5    22123425   65382920  0

In the example the only match is row 3, and the value 0 from the dummy column should be inserted in col3 row3. I've tried to make a look-up table, a function of for and if, but not found a solution when requiring matches in two dataframes. (No need to say I guess, but I'm new to R and programming..)