Summary
Prior to pseudowire emulation, Layer 2 VPN services were provided by legacy Layer 2 VPN technologies, such as ATM, Frame Relay, and VPDN, which rely on overlapping parallel network infrastructures.Pseudowire emulation is the fundamental building block of the new generation of Layer 2 VPN architectures. Many complex network applications that are to replace legacy Layer 2 VPNs or facilitate new requirements are built on top of some form of pseudowire emulation. Cisco offers AToM and L2TPv3 for pseudowire emulation. They are not designed as competing technologies; rather they are optimized for MPLS- and IP-based network infrastructures, respectively. Before determining which product to adopt, consider the technical and business factors and find the right balance between features and manageability. Each has its own merits and implications, some of which are outlined in Table 3-2.Table 3-2. Cisco Pseudowire Emulation Products Comparison Product NameAToML2TPv3 | Network Infrastructure | IP/MPLS | IP | | Signaling Protocol | Directed LDP | L2TPv3 | | Transport Layer Encapsulation | MPLS label encoding | IPv4 | | Supported Layer 2 Protocols | PPP, HDLC, Ethernet, Ethernet VLAN, Frame Relay, ATM AAL5, ATM Cell | PPP, HDLC, Ethernet, Ethernet VLAN, Frame Relay, ATM AAL5, ATM Cell | | Authentication | TCP MD5 | Shared Secret with Message Digest | | Keepalive Mechanism | Unreliable out-of-band LDP keepalive; requires new protocol extensions for reliable connectivity report | Reliable and simple in-band keepalive | | Advanced Services | Traffic engineering, QoS guarantee, fast rerouting | IPSec, IP Diffserv, Path MTU discovery, IP fragmentation | | Interoperability | Wide vendor and carrier support, good and improving interoperability | Limited vendor and carrier support |
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