Abstract: Label Switching Routers (LSR), such as IP switching of Ipsilon, use separate Virtual Circuits (VC) from different sources even having the same destination. Merging switches, on the other hand, allow multiple VCs of upstream traffic to use a single output VC if having same destination criteria. In this paper, we study IP switching of Ipsilon and identify certain security threats. We found that oscillation between routing and switching as a result of a malicious frequent suspension and releasing of flows is a main security threat that decreases performance of such systems. To stabilize the performance in face of such an attack, we propose to utilize merging switches to mitigate the implications of oscillation in LSR. The simulation results enhances this claim.