I was working in Houston, Texas this week and caught some testing of the federal interoperability repeaters.
On Thursday evening, I caught traffic from Houston FBI to various federal and state agencies on 170.7250 MHz and 171.4375 MHz. Both were using P-25 with a NAC of 653. The 170.7250 MHz channel is known as COMMAND and 171.4375 MHz is called PATCH. These same frequencies are used in other cities and are part of the DoJ 25-Cities Project.
I seem to recall some reports of these same two frequencies being used by the Houston FBI field office. When they use these repeaters, they called them L-1 and L-2, probably referring to the channel numbers on their radios.