Answers to Review Questions 201

Answers to Review Questions

1.D. A route distinguisher is 64 bits long.

2.A. VPN names are case-sensitive. It is best to have a well-defined naming convention so things don’t get too confusing.

3.D. MP-BGP must be configured to allow the exchange of VPN routing information, VPN labels, etc.

4.B. MP-BGP neighbors need to be activated.

5.B. The command to configure a VRF is ip vrf vpn_name. Don’t forget, the VRF name is case-sensitive.

6.A. The command to configure a route distinguisher is rd #.#.

7.C, D. For MP-BGP to work right, you must specify an extended community with the send-community extended command. Alternatively, you can send both extended and standard communities with the send-community both command.

8.C. The command to enter MP-BGP configuration from BGP is address-family vpnv4.

9.D. The VPNv4 address consists of the standard NLRI (32 bits) plus the route distinguisher (64 bits) for a grand total of 96 bits.

10.A. The recommended route distinguisher format is the service provider autonomous system (AS) number (16 bits), followed by a colon, and then followed by a number that’s significant to the service provider (32 bits). Therefore, 16:32 is the correct answer.

11.D. The VRF is like a mini routing table within a router. A VRF makes it seem like there are multiple logical routers.

12.A. The 64-bit route distinguisher is prepended to the NLRI, keeping addresses from overlapping in MP-BGP.

13.C. A VRF is its own separate entity. The VRF does not have any routes from the global routing table.

14.A. An MPLS VPN is just as good as an overlay VPN.

15.B. P routers run only an IGP. P routers don’t need to know any of the customer’s VPN routers to do their job of label-switching packets.

202Chapter 5 MPLS VPNs

16.C. Packets enter the network at the edge as unlabeled IP. The edgeLSR imposes the VPN label.

17.C. BGP sends no communities by default.

18.B. The global, or regular routing table, on a PE router contains the service provider routes only.

19.A. Only customer routes show up in the VRF.

20.B. With BGP, when a connection is between routers in the same AS, it is called Internal BGP (IBGP). For MP-BGP routers in the same AS, the connection is MP-IBGP.

Chapter 5, “MPLS VPNs,” introduced you to most, but not all, of the required configuration commands and technology necessary to implement a simple MPLS-based VPN. This chapter will introduce you to route targets and virtual routing and forwarding (VRF) table route redistribution.

In this chapter, all of the pieces that you’ve seen so far will be unified into an end-to-end network solution. You’ll learn how to configure a simple MPLS VPN using RIP as the CE routing protocol. In addition, in an actual network, you’ll learn the configuration, verification, and troubleshooting of a simple MPLS VPN.

A Review of VPNs

Before I start talking about routing inside MPLS VPNs, let’s first review what you’ve already learned. Point-to-point connections, or leased lines, are dedicated private links through a service provider network. Point- to-point links offer guaranteed bandwidth and privacy through a service provider network, but they’re expensive.

VPNs emerged as an alternative to dedicated point-to-point links. VPNs deliver the same benefits of dedicated point-to-point links but without the high cost. There are many technologies that are used to support overlay VPNs. From a Layer 1 perspective, VPNs can be implemented with SONET, T1, E1, ISDN, etc. From a Layer 2 perspective, VPNs can be implemented with Frame Relay, ATM, X.25, etc. From a Layer 3 perspective, IP tunneling technologies such as IPSec and GRE can be used to implement a VPN.

A few years ago, peer-to-peer VPNs were introduced. The biggest difference between peer-to-peer VPNs and traditional VPNs is that in a peer-to-peer VPN, a customer and a service provider exchange routing information. The two ways to implement peer-to-peer VPNs are dedicated router and shared router.