CCIE Routing and Switching v5.0 Official Cert Guide: IP Forwarding (Routing)

Blueprint topics covered in this chapter:

This chapter covers the following subtopics from the Cisco CCIE Routing and Switching written exam blueprint. Refer to the full blueprint in Table I-1 in the Introduction for more details on the topics covered in each chapter and their context within the blueprint.

• Cisco Express Forwarding Concepts
• Routing Protocol Migration
• Policy-Based Routing

This chapter begins with coverage of the details of the forwarding plane—the actual forwarding of IP packets. This process of forwarding IP packets is often called IP routing, or simply routing. Also, many people also refer to IP routing as the data plane, meaning the plane (topic) related to the end-user data.

Chapters 7 through 11 cover the details of the IP control plane. In contrast to the term data plane, the control plane relates to the communication of control information—in short, routing protocols like OSPF and BGP. These chapters cover the routing protocols on the exam, plus an additional chapter on redistribution and route summarization.

“Do I Know This Already?” Quiz

Table 6-1 outlines the major headings in this chapter and the corresponding “Do I Know This Already?” quiz questions.

Table 6-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

To best use this pre-chapter assessment, remember to score yourself strictly. You can find the answers in Appendix A, “Answers to the ‘Do I Know This Already?’ Quizzes.”

1. What command is used to enable CEF globally for IPv4 packets?

   1. enable cef
   2. ip enable cef
   3. ip cef
   4. cef enable
   5. cef enable ip
   6. cef ip

2. What command is used to enable CEF globally for IPv6 packets?

   1. enable cef6
   2. ipv6 enable cef
   3. ipv6 cef
   4. ip cef (the command automatically enables CEF for IPv4 and IPv6)

3. Can CEF for IPv6 be enabled independently of CEF for IPv4?

   1. Yes
   2. No

4. Which of the following triggers an update to a CEF FIB?

   1. Receipt of an ICMPv6 Neighbor Advertisement message with previously unknown information
   2. Receipt of a LAN ARP reply message with previously unknown information
   3. Addition of a new route to the IP routing table by EIGRP
   4. Addition of a new route to the IP routing table by adding an ip route command
   5. The removal of a route from the IP routing table by EIGRP

5. Which of the following triggers an update to a CEF adjacency table?

   1. Receipt of a CDP multicast on the PVC connected to Router1
   2. Receipt of an ARP response with previously unknown information
   3. Receipt of a packet that needs to be routed to another router over a point-to-point interface
   4. Receipt of an ICMPv6 Neighbor Advertisement with previously unknown information

6. Which of the following packet-switching paths is considered to be the slowest?

   1. Process Switching
   2. Fast Switching
   3. Route Cache
   4. Cisco Express Forwarding

7. Which of the following commands is used on a Cisco IOS Layer 3 switch to use the interface as a routed interface instead of a switched interface?

   1. ip routing or ipv6 unicast-routing global command
   2. ip routing or ipv6 unicast-routing interface subcommand
   3. ip address interface subcommand
   4. switchport mode routed interface subcommand
   5. no switchport interface subcommand

8. On a Cisco Catalyst 3560 switch, the first line of the output of a show interface vlan 55 command lists the state as “Vlan 55 is down, line protocol is down.” Which of the following might be causing that state to occur?

   1. VLAN interface has not been no shut yet.
   2. The ip routing global command is missing from the configuration.
   3. On at least one interface in the VLAN, a cable that was previously plugged in has been unplugged.
   4. VTP mode is set to transparent.
   5. The VLAN has not yet been created on this switch, or is not in the active state.

9. On a Cisco Catalyst 3560 switch, the first line of the output of a show interface vlan 55 command lists the state as “Vlan 55 is up, line protocol is down.” Which of the following might be causing that state to occur?

   1. VLAN interface has not been no shut yet.
   2. The ip routing global command is missing from the configuration.
   3. There is no switch port on the switch with this VLAN allowed and in the STP forwarding state.
   4. STP has been administratively deactivated for this VLAN.
   5. The VLAN has not yet been created on this switch, or is not in the active state.

10. Imagine a route map used for policy routing, in which the route map has a set default interface serial0/0 command. Serial0/0 is a point-to-point link to another router. A packet arrives at this router, and the packet matches the policy routing route-map clause whose only set command is the one just mentioned. Which of the following general characterizations is true?

    1. The packet will be routed out interface s0/0; if s0/0 is down, it will be routed using the default route from the routing table.
    2. The packet will be routed using the default route in the routing table; if there is no default, the packet will be routed out s0/0.
    3. The packet will be routed using the best match of the destination address with the routing table; if no match is found, the packet will be routed out s0/0.
    4. The packet will be routed out interface s0/0; if s0/0 is down, the packet will be discarded.

11. Router1 has an fa0/0 interface and two point-to-point WAN links back to the core of the network (s0/0 and s0/1, respectively). Router1 accepts routing information only over s0/0, which Router1 uses as its primary link. When s0/0 fails, Router1 uses policy routing to forward the traffic out the relatively slower s0/1 link. Which of the following set commands in Router1’s policy routing route map could have been used to achieve this function?

    1. set ip default next-hop
    2. set ip next-hop
    3. set default interface
    4. set interface