Summary

This chapter covered a lot of territory. It presented different architectures for network virtualization. The basic alternative is to use some form of tunnel overlay, with your choice of protocol and at your choice of OSI layer, and a peer architecture based on RFC 2547.

In the tunnel category, we reviewed 802.1q trunks; GRE-based Layer 3 VPNs; DMVPN, which combines mGRE and IPsec; and L2TPv3 and MPLS-based p2p Layer 2 circuits. VPLS is something of a hybrid because customer and PE devices have a peer relationship of sorts, but PEs maintain a full mesh of LSPs across the core network.

In the peer category, we covered the RFC 2547 architecture and the predominant implementation using MPLS. We also discussed alternative core protocols for this architecture, using GRE and L2TPv3.

Finally, we introduced hierarchical Layer 3 VPNs. CsC has a transport MPLS VPN running "beneath" customer VPNs. Inter-autonomous system allows eBGP to allow service providers to form a peer relationship between their autonomous systems. L2TPv3 or GRE can be used to transport MPLS over IP core networks using the same extensions as discussed in the RFC 2547 section.

The next chapter puts these architectures to use in design scenarios relevant to enterprise networks.