Lesson 3: Redistribution Methods
In Lesson three, Narbik Kocharians continues his demonstration of using MPLS and Layer 3 VPNs by recommending a one way distribution, then running a debug on the first customer router, and finishing by sending a pinging 18.104.22.168. This tests the redistribution up to the point that needs to be configured. Narbik then demonstrates redistribution of RIP into BGP, allowing him to verify where the routes are using show route vrfca, and then by running "show ip bgp vpnv4."
Once LDP, VRF, RD, and RT are understood and configured, to configure Layer 3 VPNs is, as Narbik says, "ridiculously easy." All you need to do is play the redistribution game.
Narbik spends a moment to focus on the V label, or the VPN label. Narbik explains that you can have multiple labels in a given packet. The top label is originated by LDP, which advertises it to its LDP neighbors. This is the first application of MPLS. The second application of MPLS is Layer 3 VPNs, which use a different label called the V label. Narbik then takes us into the configuration of the control and data planes of the LDP label, and the V label.
He begins by setting up a scenario with five routers. Routers 1 and 5 are the PE routers, and the others are core routers. Every router locally originated a label for the given prefix on Router 1, which is 22.214.171.124. Then the routers start to advertise the label that it originated to their neighboring LSR. This means that if Router 5 wants to connect to network to 126.96.36.199, it has to attach its label and send it to Router 4, which performs the same action, and is repeated throughout the other Routers until Router 2 is reached. Router 2 pops the label, and give it to Router 1 as a pure IP address. Narbik then takes us through the scenario of Router 5 receiving a route from a customer, and what must be done to be sent to Router 1.
Narbik then covers EIGRP by explaining how to run EIGRP through a CA and PE router. To do this, he configures the CA router, and then the PE router. After performing the route distribution, Narbik verifies them for both PE routers, and ensures that everything is working, and he notes that this process is similar, if not identical, to RIP. At this point in the demonstration, Narbik then configures OSPF over the MPLS, and discusses the process of using Sham-Link. Sham-Link overcomes the OSPF default behavior for selecting an intra-area backdoor route between VPN sites instead of an inter-area (PE to PE) route. Narbik explains this is to provide backup connection and provides a thorough explanation of how.