External Clock set to 64MHz on USRP2/N210

Hello All,

There was a previous project done in my research group where a external
device generates a 64 MHz clock to the USRP1 in addition to a PPS
signal. Currently I am making appropriate changes so a similar project
can be used for the USRP2/N210. I was wondering if the same 64MHz
external clock is connected to the USRP2, would this override the
default 100MHz master clock? I am still fairly new to the USRP, so this
could be a very trivial question. My understanding right now is that an
external reference clock has to be equal to an integer division of
100MHz (i.e 100MHz/n), but this could be totally wrong. Any advice on
this issue would be greatly appreciated.

Thank you very much,