Answers to Review Questions 117
Answers to Review Questions
1.B. One of the requirements for MPLS is that control-plane information be exchanged using pure unlabeled IP.
2.D. For frame-mode MPLS, or tag switching, a PVC needs to be set up between LSRs. The ATM switches have no MPLS functionality, and the PVC is set up as normal.
3.A. Routers with interfaces such as Ethernet, PPP (serial), and HDLC (serial) run frame-mode MPLS.
4.A. An ATM switch enabled with MPLS is referred to as an ATM-LSR.
5.C. An LSC communicates with an ATM-LSR over VC 0/32.
6.A, C. Cell-mode MPLS uses ordered control and downstream-on- demand to assign labels.
7.D. ATM switches can’t read labels; therefore they must switch traffic based on the VPI/VCI values.
8.C. The configuration is being performed on an ATM edge LSR. The point-to-point option indicates frame-mode MPLS.
9.A. The configuration is being performed on an ATM edge LSR. The mpls option indicates cell-mode MPLS.
10.B. MPLS is being configured for an ATM interface (not sub-interface), which indicates that MPLS is being enabled on an ATM-LSR. The mpls option indicates cell-mode MPLS.
11.D. When MPLS is enabled on an ATM-LSR, LDP is used to exchange labels. Standard ATM signaling such as UNI and PNNI is still being used on the ATM-LSR. Standard ATM and MPLS control-plane signaling run as “ships passing in the night.”
12.C. VC merge solves both cell-interleaving (ensuring the proper assembly of cells) problems and preserves labels for future use.
13.B. On an ATM edge-LSR, as the sub-interface is configured, the mpls command option is applied for cell-mode MPLS.
14.C. On an ATM edge-LSR, as the sub-interface is configured, the point-to-point command option is applied for frame-mode MPLS.
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118Chapter 3 MPLS and ATM
15.A. On an ATM edge-LSR, as the sub-interface is configured, the tagswitching command option is applied for cell-mode tag switching.
16.A. To enable VC merge on an ATM-LSR, use the mpls ldp atm vc-merge command.
17.A. VC merge is enabled by default on a Cisco IOS ATM-LSR.
18.A. The default hop-count object TLV value is 254. This can be changed based on network requirements.
19.C. The routing protocol is used to prevent loops in both frame-mode and cell-mode MPLS.
20.B. Tag switching is being configured for an ATM interface (not subinterface), which indicates that tag switching is being enabled on an
ATM-LSR.
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Chapter
4
VPNs: An Overview
CCIP MPLS EXAM TOPICS COVERED IN THIS CHAPTER:
Identify major virtual private network topologies, their characteristics, and usage scenarios.
Describe the differences between an overlay VPN and a peer-to-peer VPN.
List the major technologies supporting overlay VPNs and peer-to-peer VPNs.
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