CCNP Route FAQ: Policy-Based Routing and IP Service Level Agreement

CCNP Route FAQ: Policy-Based Routing and IP Service Level Agreement


Figure: Sending and Receiving Packets with IP SLA

Q1. Policy-Based Routing (PBR) has been enabled on Router R1’s interface F0/0. Which of the following is true regarding how PBR works? (Choose two.)
a. Packets entering F0/0 will be compared based on the PBR route map.
b. Packets exiting F0/0 will be compared based on the PBR route map.
c. IOS ignores the PBR forwarding directions when the packet matches a route map deny clause.
d. IOS ignores the PBR forwarding directions when the packet matches a route map permit clause.

Answer: A and C. PBR supports processing packets on an interface, for the inbound direction only. The referenced route map causes PBR to attempt policy routing of packets that match a permit clause in the route map.

Q2. Examine the following configuration on Router R1. R1’s show ip route 172.16.4.1 command lists a route with outgoing interface S0/1/1. Host 172.16.3.3 uses telnet to connect to host 172.16.4.1. What will Router R1 do with the packets generated by host 172.16.3.3 because of the telnet, assuming the packets enter R1’s F0/0 interface? (Choose two.)

a. The packet will be forwarded out S0/0/1, or not at all.
b. The packet will be forwarded out S0/0/1 if it is up.
c. The packet will be forwarded out S0/1/1 if it is up.
d. The packet will be forwarded out S0/1/1 if it is up, or if it is not up, out s0/0/1.
e. The packet will be forwarded out S0/0/1 if it is up, or if it is not up, out s0/1/1.

Answer: B and E. Packets created by Telnet use TCP, so the packet will match ACL 101 with a permit action. So, PBR will match the only route map clause shown in the configuration, with that permit route map clause listing a set command. The set command lists S0/0/1 as the outgoing interface, and without a default parameter. So, Router R1 will first attempt to forward the packet based on the set command (interface S0/0/1), but if the interface is down, then try to forward based on the IP routing table (interface S0/1/1).

Q3. The following output occurs on Router R2. Which of the following statements can be confirmed as true based on the output from R2?

a. R2 will forward all packets that enter Fa0/0 per the PBR configuration.
b. R2 will use route map RM2 when determining how to forward packets that exit interface Fa0/1.
c. R2 will consider using PBR for all packets exiting S0/0/0 per route map RM3.
d. R2 will consider using PBR for all packets entering S0/0/0 per route map RM3.

Answer: D. The output from the show ip policy command shows the interfaces on which PBR has been enabled, and the name of the route map enabled for PBR on each interface. For the purposes of this question, the output tells us the interfaces on which PBR has been enabled. Two answers mention packets exiting the interface, so these answers cannot be correct, because PBR applies to packets entering an interface. For the two interfaces that mention inbound packets, one suggests that all packets will be forwarded per the PBR configuration; some may not be forwarded per PBR, depending on the configuration of the route map. The correct answer specifically mentions that PBR will consider all packets with PBR, which is the more accurate statement about PBR operations.

Q4. Which of the following are examples of traffic that can be created as part of an IP Service-Level Agreement operation? (Choose two.)
a. ICMP Echo
b. VoIP (RTP)
c. IPX
d. SNMP

Answer: A and B. The IP SLA feature focuses on IP traffic, so IOS does not include Novell’s older IPX protocol as part of IP SLA. IP SLA uses SNMP MIBs to store statistics, but it does not use SNMP as an operation.

Q5. The following configuration commands exist only in an implementation plan document. An engineer does a copy/paste of these commands into configuration mode on Router R1. Which of the following answers is most accurate regarding the results?

a. The SLA operation will be configured but will not start until additional commands are used.
b. The SLA operation is not completely configured so it will not collect any data.
c. The SLA operation is complete and working, collecting data into the RTTMON MIB.
d. The SLA operation is complete and working but will not store the data in the RTTMON MIB without more configuration.

Answer: C. The three lines shown create the operation number (first command), define the operation (second command), and start the operation (third command). All commands are correct. After the operation is started, IP SLA stores the data in the RTTMON MIB–no additional configuration necessary.

Q6. The following output occurs on Router R1. IP SLA operation 1 uses an ICMP echo operation type, with default frequency of 60 seconds. The operation pings from address 1.1.1.1 to address 2.2.2.2. Which of the following answers is true regarding IP SLA and object tracking on R1?

a. The tracking return code fails after the SLA operation results in an ICMP echo failure three times.
b. The tracking return code fails after the SLA operation results in an ICMP echo failure one time.
c. After the tracking object fails, the tracking object moves back to an up state 45 seconds later in all cases.
d. After moving to a down state, the tracking object moves back to an OK state 45 seconds after the SLA operation moves to an OK state.

Answer: D. The up timers on the tracking object defines how long to wait, when in a down state, after seeing the IP SLA object transition to an OK state. Similarly, the down timer defines how long to wait, when in an OK state, after seeing the IP SLA object move to a down state, before moving the tracking object to a down state.

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James Palmer

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