We upgraded our 7206VXR from an NPE-300 to a NPE-G1. After doing so we lost our frame relay remote sites. After 2 hours with TAC the engineer changed the MTU on the DS3 on the 7206 from 4470(default) to 1500 and all our frame relay sites came up. All our remote 1601 routers were already set to an MTU of 1500. I just need to know why this small change caused all our sites to come back up. The NPE-300 worked fine with MTU 4470 so is this something new on the G1?