Based on the analysis of 802.11 link-layer handoff and representative cross-layer mechanisms supporting mobility, this paper proposes a Locator/Identifier Split Network Based Cross-Layer Roaming Mechanism (LISN-CLRM) with the Layer 2 and Layer 3 handoff coupling organically. Theoretical analysis shows that the total delay of this mechanism is much smaller than MIPv6, and is 77.5 ms smaller than SMOS[1]. By pre-registration on Layer 2, our mechanism effectively reduces the handoff delay and overhead and basically meets the demand of real-time business.