370 Chapter 8 Advanced MPLS Topics

On PE3 and PE4, the following configuration exists for CustomerB_VPN:

ip vrf customerb_vpn route-target export 517:38 route-target import 517:38

For an overlay VPN topology, CustomerA_HQ and CustomerB_HQ need to know each other’s routes. They both will import and export a route target of 517:2067. The configuration, for CustomerA_HQ, on PE2 is as follows:

ip vrf customera_vpn route-target export 517:1 route-target import 517:1 route-target export 517:2067 route-target import 517:2067

The configuration, for CustomerB_HQ, on PE3 is as follows:

ip vrf customerb_vpn route-target export 517:38 route-target import 517:38 route-target export 517:2067 route-target import 517:2067

Summary

In addition to using RIPv2 as a PE-CE routing protocol as discussed in Chapter 6, “MPLS VPNs and RIP,” or OSPF as discussed in Chapter 7, “MPLS VPNs and OSPF,” static routes and E-BGP are supported for use in MPLS VPNs. For static routes, a static route is specified with the ip route vrf vpn_name command. Don’t forget that this route must be redistributed into MP-BGP with the redistribute static command.

An E-BGP connection can be made between a PE and CE router. BGP is a wonderful protocol in that you have advanced filtering and control mechanisms that can be configured. To prevent a network from accepting a malicious number of routes, the maximum routes command can be used to limit the number of routes in a VRF. When configuring an E-BGP connection, the neighbor needs to be activated. For topologies where the same AS number is reused, the AS-override allows the service provider to override the AS path.

Key Terms 371

In addition to simple MPLS VPN topologies, the route distinguisher allows for the support of many more complex topologies. This chapter introduced you to overlay and Central Services MPLS VPN topologies. An overlay VPN is where a site participates in more than one VPN at a time. A Central Services VPN is where some central point must be accessed by several sites, but those sites do not have routing knowledge of each other.

Exam Essentials

Understand static routing for use in MPLS VPNs. If you don’t want the associated overhead of running a routing protocol between a PE and CE router, static routes are supported for MPLS VPNs. To configure a static route, use the ip route vrf vpn_name command. Don’t forget to redistribute the static route into MP-BGP.

Understand E-BGP for use in MPLS VPNs. E-BGP is supported as a PE-CE routing protocol. When configuring an E-BGP connection to

a CE device, the neighbor must be activated. For cases where the same AS number is being reused, the as-override command can be used to override the AS path.

Understand complex VPN topologies. An overlay VPN is a topology where a site participates in more than one MPLS VPN. A Central Services VPN topology is the name of a topology where sites connect to some centralized server or service. The sites don’t have routing information about each other, only about the Central Services site. The Central Services site has routing knowledge of all sites.

Key Terms

Before you take the exam, be certain you are familiar with the following terms:

372 Chapter 8 Advanced MPLS Topics

Review Questions

1.Which command do you use to place a static route into MP-BGP?

A.redistribute connected

B.redistribute static

C.redistribute vrf static

D.None of the above

2.For static VRF routes, the outgoing interface is ___________.

A.Mandatory

B.Optional

C.None of the above

3.For static VRF routes, the next hop IP address is ___________.

A.Mandatory

B.Optional

C.None of the above

4.What command is used to configure a static VRF route?

A.ip route

B.ip route vrf vpn_name

C.ip vrf vpn_name route

D.ip vrf route vpn_name

5.What command is used to configure a standard static route?

A.ip route

B.ip route vrf vpn_name

C.ip vrf vpn_name route

D.ip vrf route vpn_name

Review Questions 373

6.What command is used to advertise the subnets of interfaces in a VRF?

A.redistribute static

B.redistribute connected vrf vpn_name

C.redistribute connected

D.redistribute vrf vpn_name connected

7.Which of the following routing protocols is not supported as a PE-CE routing protocol?

A.RIPv2

B.E-BGP

C.EIGRP

D.OSPF

8.E-BGP neighbors must be ___________.

A.Redistributed

B.Activated

C.Upgraded

D.None of the above

9.Customers connecting to a PE using E-BGP ___________ need to be upgraded to the latest MPLS IOS.

A.Do

B.Do not

C.None of the above

10.Which one of the following features is used to address problems associated with reusing the same AS number between customer sites?

A.AS path prepending

B.AS-override

C.Maximum routes

D.VC merge

374Chapter 8 Advanced MPLS Topics

11.Without AS-override, where customer sites reuse the same AS number, routers think there is a ___________.

A.Down interface

B.Multihoming

C.Routing loop

D.None of the above

12.Which of the following commands is used to configure AS-override?

A.neighbor ip_address as-override

B.neighbor ip_address as override

C.neighbor ip_address as-override activate

D.neighbor ip_address as-override vrf vpn_name

13.E-BGP routes ___________ need to be redistributed into MP-BGP.

A.Do

B.Do not

C.May

14.Which of the following features is used to limit the number of routes in a VRF?

A.AS path prepending

B.AS-override

C.Maximum routes

D.VC merge

Review Questions 375

15.In the following code snippet, what is the maximum number of routes allowed in the VRF?

ip vrf vpn-X rd 1000:1

route-target both 1000:1 maximum-routes 10 75

A.1000:1

B.10

C.75

D.None of the above

16.Once the maximum number of routes has entered a VRF when configured with the maximum-routes command, additional routes will be ___________.

A.Dropped

B.Permitted

C.Permitted with a message being sent to a SYSLOG server

D.None of the above

17.Two sites connected in a VPN topology where the route-target both command was used is most likely a ___________.

A.Simple MPLS VPN

B.Overlay MPLS VPN

C.Central Services MPLS VPN

18.Which topology best represents the situation where a site participates in more than one VPN?

A.Simple MPLS VPN

B.Overlay MPLS VPN

C.Central Services MPLS VPN

376Chapter 8 Advanced MPLS Topics

19.Which of the following topologies represents a site that can see all other sites, but the other sites can see it and not each other?

A.Simple MPLS VPN

B.Overlay MPLS VPN

C.Central Services MPLS VPN

20.Which of the following features is used to prevent a malicious flooding of routes into the service provider backbone?

A.AS path prepending

B.AS-override

C.Maximum routes

D.VC merge