Not sure if VLOOKUP is what I need, tried and it did not work very well.

I have 2 sheets, they both contain 2 colums.
Sim & Modem, both these consist of a set of numbers.

I need to compare a master sheet against another sheet, like this:

Master
Sim Modem
123 345
355 233

Other
Sim Modem
123 345
355 342

I need to try and compare the sim number matchs the modem number next to it on the other sheet using the master as the source, and in some way mark it what matches, there are about 300 rows.

Thanks in advance for any help.