Lesson 1: Introduction to MPLS and Layer 3 VPNs
In this free training video about Multiprotocol Layer Switching, or MPLS, and Layer 3 VPNs, Narbik Kocharians begins by describing what this webinar will be discussing including LDP, VRF, route distinguishers, and route targets. Once an understanding of these terms has been achieved, Layer 3 VPNs, and what happens between the PE and CE routers can be understood. In this process, he will be discussing RIP, EIGRP, OSPF, and BGP.
In his demonstration, Narbik sets up a scenario with three routers, which have some type of connection between them. He walks you through what the control and data planes consist of and begins by discussing what routing protocol you need. For this demonstration, Narbik uses OSPF for its traffic engineering capability. After completing the control plane, Narbik moves to start populating the data plane using FIB (Forward Information Base), which is a combination of RIB and a Layer 2 table. Narbik then pings the router to demonstrate how FIB works with the routers to show a predictable behavior.
Narbik then uses LDP, or Label Distribution Protocol in the control plane to perform a route table lookup and assigns a label to every network to every router it sees in the routing table, moving it into Label Information Base or LIB. After completing the control plane table, Narbik then moves to populating the data plane with LFIB, or Label Forwarding Information Base. Once that is complete, Narbik walks through OSPF configuration by beginning with running router OSPF through a network connect, and performs a similar configuration for MPLS with LDP. He then assigns a router ID to the router OSPF.
Once the configuration basics are complete, Narbik spends a minute to talk about how labels will play into the configuration as well. The question that Narbik brings up next is which label is assigned to Router 1's IP address by which LSR, or Label Switching Router. By assigning an MPLS label range, he can then see which Router assigned it. Once the routers locally assign labels to the particular IP address Narbik has set, the routers then advertise the label that they originated into their neighboring LDP.
The process of Liberal Label Retention is then begun, and Narbik breaks down what happens when he sends a ping. Narbik then explains how the routers can distinguish between label and IP packets by using a protocol, and what happens when the routers receive each one. In this scenario that Narbik has built, he has Router 1 receiving a label packet, which means Router 1 has to do two table lookups. In fact, any router that advertises any network has to do two table lookups.
Narbik explains the need for penultimate or second last hopper (or php) to accommodate for the two table lookups that the routers need to perform when receiving a label packet. He then explains the "pop" that occurs and breaks down how that affects the LIB and the FIB of Router 1.
After discussing what occurs when that penultimate hop process is implemented, Narbik thoroughly explains the need for labels by setting up a scenario of three routers with full reachability to each other. Can router 3 ping the IP address for 126.96.36.199 on Router 1? No. This illustrates the point that while aspects of the control plane work, the data plane failed, which needs to be fixed. In setting up a GRE tunnel to send the packet through, Router 3 can now ping Router 1. Narbik calls LDP "nothing but a tunnel," and demonstrates that if Router 2 is the core of the MPLS network, it is now BGP free by pushing the muscle routers to the edge. This is the benefit of running MPLS and Layer 3.
Narbik then describes the process of offering MPLS and Layer 3 networks in the US. He sets up a two PE routers and connects them through a cloud. First, Narbik configures an IBGP pier session. Second, promotes VLANs to Layer 3, and they become VRFs. Once the VRFs for each hypothetical customer are established, Narbik takes you through how they are configured.