Key Terms 111

configuration on an ATM edge-LSR are as follows:

interface ATM1/0 no ip address

!

interface ATM1/0.1 point-to-point

Remember that on the ATM edge-LSR, it is the point-to-point option on the sub-interface configuration that makes it frame-mode MPLS.

Describe the loop detection and prevention mechanisms in MPLS.

Both frame-mode and cell-mode MPLS use the routing protocol to prevent routing loops. For MPLS, the TTL field from the IP TTL is decremented by 1 by the ingress edge-LSR, and then copied into the MPLS label TTL field. Upon exiting the MPLS network, the MPLS label TTL value is copied back into the IP TTL field. For cell-mode MPLS, instead of the TTL value, Cisco uses the LDP hop-count object TLV. When an ATMLSR receives a Label Request message with the LDP hop-count object TLV, it increments the hop-count value by 1. The default Cisco hop count is 254, and that value is configurable. Once this value is reached, a loopdetected message is sent to the device that originated the label request.

Key Terms

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

112 Chapter 3 MPLS and ATM

Review Questions

1.It is an MPLS requirement that control-plane traffic be exchanged using ___________.

A.Broadcast

B.Unlabeled IP

C.Multicast

D.Labeled IP over VC 0/32

2.Which of the following needs to be set up on an ATM switch for frame-mode MPLS?

A.MPLS or tag switching

B.A sub-interface with the point-to-point option configured

C.VC 0/32

D.PVC

3.Routers with serial interfaces run ___________ MPLS.

A.Frame-mode

B.Cell-mode

4.Which of the following terms best describes a core ATM switch with MPLS enabled?

A.ATM-LSR

B.ATM edge-LSR

C.LSR

D.None of the above

5.An LSC communicates with an ATM-LSR on which of the following VCs?

A.0/1

B.0/7

C.0/32

D.0/4096

Review Questions 113

6.Which of the following methods is used by cell-mode MPLS to bind labels? (Choose two.)

A.ordered control

B.independent control

C.downstream-on-demand

D.unsolicited downstream

7.Cell-mode MPLS does not switch traffic based on a label but instead uses the ___________ values.

A.SVC/PVC

B.DLCI

C.VCI/VIP

D.VPI/VCI

8.Based on the following code, what is being configured?

interface ATM1/0 no ip address

!

interface ATM1/0.1 point-to-point

ip address 192.168.1.5 255.255.255.0 pvc 0/100

encapsulation aal5snap mpls ip

A.MPLS is being configured for cell mode on an ATM edge-LSR.

B.Cell-mode MPLS is being configured on an ATM-LSR.

C.Frame-mode MPLS is being configured on an ATM edge-LSR.

D.Frame-mode MPLS is being configured on an ATM-LSR.

9.Based on the following code, what is being configured?

interface ATM1/0 no ip address

!

interface ATM1/0.1 mpls

114Chapter 3 MPLS and ATM

A.MPLS is being configured for cell mode on an ATM edge-LSR.

B.Cell-mode MPLS is being configured on an ATM-LSR.

C.Frame-mode MPLS is being configured on an ATM edge-LSR.

D.Frame-mode MPLS is being configured on an ATM-LSR.

10.Based on the following code, what is being configured?

interface ATM1/0 mpls ip

A.MPLS is being configured for cell-mode on an ATM edge-LSR.

B.Cell-mode MPLS is being configured on an ATM-LSR.

C.Frame-mode MPLS is being configured on an ATM edge-LSR.

D.Frame-mode MPLS is being configured on an ATM-LSR.

11.ATM-LSRs use which of the following signaling protocols to exchange labels?

A.UNI

B.MNI

C.PNNI

D.LDP

12.Which capability does Cisco use to preserve labels and ensure the proper assembly of cells?

A.Cell interleaving

B.LDP

C.VC merge

D.None of the above

13.Which of the following command options configures an ATM edgeLSR for cell-mode MPLS?

A.tag-switching

B.mpls

C.point-to-point

D.cell-mode

Review Questions 115

14.Which of the following command options configures an ATM edgeLSR for frame-mode MPLS?

A.tag-switching

B.mpls

C.point-to-point

D.cell-mode

15.Which of the following command options configures an ATM edgeLSR for cell-mode tag switching?

A.tag-switching

B.mpls

C.point-to-point

D.cell-mode

16.Which of the following commands enables VC merge on an ATM-LSR?

A.mpls ldp atm vc-merge

B.mpls ip atm vc-merge

C.mpls ip atm vcmerge

D.mpls ip atm vc merge

17.By default, VC merge is ___________.

A.Enabled

B.Disabled

18.For cell-mode MPLS, the default hop-count object TLV value is ___________.

A.254

B.16,534

C.256

D.16,536

116Chapter 3 MPLS and ATM

19.Which of the following is used by both frame-mode and cell-mode MPLS to prevent loops?

A.TLV

B.TTL

C.Routing protocol

D.None of the above

20.Based on the following code, what is being configured?

interface ATM1/0 tag-switching ip

A.Tag switching is being configured for cell-mode on an ATM edge-LSR.

B.Cell-mode tag switching is being configured on an ATM-LSR.

C.Frame-mode tag switching is being configured on an ATM edge-LSR.

D.Frame-mode tag switching is being configured on an ATM-LSR.