The layered nature of the network architecture allows for the substitution of one link-layer technology for another, as we have seen in recent classes; interchangeable use of ethernet or wi-fi, for instance. In this lecture, we explore the idea of inserting an entire network stack as the link-layer technology. We will examine how this virtualization allows ISPs to use an ATM network for high-bandwidth transport between border routers, for instance. We will also look at MPLS, an exciting (fairly) new technology for labeling flows at the link-layer and making routing decisions based on the labels. MPLS is a generic technology that can enable all sorts of interesting business and research opportunities. I highly recommend interested students learn more about MPLS.
By the end of this lesson, the student will be able to:
describe the use of virtual LANs (VLAN) to allow multiple subnets to be connected with a single port-based switch. Be sure to include broadcast domain separation, flexibility for re-assigning hosts within the VLAN, connection mechanisms for when the same VLAN is connected across switches.
describe how link virtualization allows links to be more than just a simple "channel connecting adjacent nodes"
diagram the encapsulation of messages inside segments inside packets inside frames. Ensure you can handle cases such as ICMP and ARP.
describe MPLS, including advantages, labeled frame formats (why is the label between link-layer and IP headers?), router operations. Be able to describe what an MPLS forwarding table might look like, given some MPLS enabled network scenario.