Populate a new column in dataframe, based on values in differently indexed dataframe

Question

I have two dataframes, each with a different index, and I'd like to merge the 'hop' column from df2 into df1 based on the 'src' column in df1 and the index in df2.

df1
     src    dest    val
  0    1       2      X
  1    1       2      Y
  2    1       3      Z
  3    1       4      X
  4    2       2      X
  5    3       2      Y
  6    4       3      Z
  7    4       1      X

df1
 id  hop   
  1    3
  2    5
  3    2
  4    3

i.e. the resulting dataframe needs to be merged as such:

df3
     src    dest    val    hop
  0    1       2      X      3
  1    1       2      Y      3 
  2    1       3      Z      3
  3    1       4      X      3
  4    2       2      X      5
  5    3       2      Y      2
  6    4       3      Z      3
  7    4       1      X      3

I think it's probably a pd.merge() or pd.join() operation but I'm having a spot of bother with it :(