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Exam A
A packet that needs to be forwarded arrives on an interface of a router. In order for a router to route data, what must that router determine? (Select the best answer)
A. The route age of the next-hop device
B. The subnet mask of the source network
C. The cost metric of the path of the destination
D. The outbound interface of the best path to the destination
E. All of the above

Correct Answer: D Section: (none) Explanation
Explanation: In order to route the data to the correct destination the router must know the outbound interface that provides the best destination. When a receives a packet that needs to be forwarded, the router determines the destination network, looks up the best path to that destination in the routing table, and then forwards the packet out the correct interface. Incorrect Answers:
A. The age of the next-hop router is not consulted before forwarding information.
B. The destination subnet mask is used by the router to determine the best path (most specific network match rule), but not the source subnet mask.
C. The cost metric is used by routing protocols to determine the best route to a destination. This best route is then installed into the routing table. The router uses the routing table to forward packets, but does not use the metrics for that specific route before forwarding each packet.

A new router is being installed into an existing network, and the routing table is being built for the first time on this network. Which of the following statements is true regarding the routing tables on a Cisco router?
A. Entries are listed in the order of the route cost metric.
B. Only the active link is shown for load-balanced routers.
C. Privileged EXEC mode is reuired to view the routing table.
D. The clear ip route * command refreshes the entire routing table.
E. All of the above are true.

Correct Answer: C Section: (none) Explanation
The show ip route command is used to display IP routing table entries. It can only be run in
privileged (enable) mode.
Incorrect Answers:

A. Entries are not listed in route cost order. Entries are ordered by destination IP address.
B. The other links in the load balanced bundle are also shown.
D. The clear ip route command is used the clear delete IP routing table entries. In particular the clear ip route * (or clear ip route all) command deletes IP routing table entries. This is not a refresh. Static routes will not be recreated.

Which of the following phrases is the correct term for what happens to a network when a topology change causes all the routers to synchronize their routing tables?
A. Flooding
B. Broadcasting
C. Convergence
D. Summarization
E. None of the above

Correct Answer: C Section: (none) Explanation
Explanation: A topology change forces a convergence of the routers to a new routing state.
Convergence is the time that it takes for all routers to agree on the network topology after a
Incorrect Answers:

A. Flooding is the process of sending out routing topology information used by link state protocols.
B. Broadcasting is used on LAN level communications. By default, routers do not forward broadcasts.
D. Summarization is the act of taking multiple routes within the routing table, and advertising them as one less specific route.

What is the purpose of configuring a router with the “IP Helper address” command?
A. IP Helper is used to direct BOOTP clients to a BOOTP server.
B. IP Helper is used to prevent the router form forwarding IP broadcasts.
C. IP Helper is used to allow IPX clients to communicate with IP-based servers.
D. IP Helper is used to accommodate compatibility routers using different IP routing protocols.

Correct Answer: A Section: (none) Explanation
Explanation: The ip helper-address command is used to have the Cisco IOS software forward User Datagram Protocol (UDP) broadcasts, including BOOTP, received on an interface. DHCP protocol information is carried inside of BOOTP packets. To enable BOOTP broadcast forwarding for a set of clients, configure a helper address on the router interface closest to the client. The helper address should specify the address of the DHCP server. Note: A DHCP server can be considered to be a BOOTP server, even though a DHCP server is more advanced. Incorrect Answers:
B. Combined with the ip forward-protocol global configuration command, the ip hel peraddress command allows you to control which broadcast packets and which protocols are forwarded. However, the main purpose of the IP helper feature is not to prevent the router from forwarding IP broadcasts.
C. IP helper does not use IPX.
D. This is false.

On router CK1 the command “ip helper address” is already configured. Which of the following commands would you use if you wanted to send SNMP broadcast packets off to a specific server?
A. ip server udp 161
B. ip helper-protocol 161
C. ip forward-protocol 161
D. ip directed-broadcast 161
E. ip forward snmp

Correct Answer: C Section: (none) Explanation Explanation/Reference:
Explanation: SNMP requests are typically sent to UDP port 161.
The ip forward-protocol command is used to specify which protocols and ports the router
forwards when forwarding broadcast packets. If an IP helper address is defined, UDP forwarding is
enabled on default ports.
Note: Syntax: ip forward-protocol {udp [port] | nd | sdns}
Incorrect Answers:

A: The use of ip server udp is not correct.
B: There is no such command.
D: The ip directed-broadcast command is used to enable the translation of directed broadcast to physical broadcasts. It does not apply in this scenario. Furthermore, an access-list with number 161 has to be configured. Syntax: ip directed-broadcast [access-list-number] | [extended access-list-number]

When you execute the “ip helper-address” command on a router, which three UDP ports get enabled automatically by default? (Select three)
A. 53 (DNS)
B. 69 (TFTP)
C. 515 (LPR)
D. 161 (SNMP)
E. 49 (TACACS) Answer: A, B, E Explanation: To forward the BootP/DHCP reuest from the client to the DHCP server, the ip helper-address interface command is used. The IP helper-address can be configured to forward any UDP broadcast based on UDP port number. By default, the IP helper-address will forward the following UDP broadcasts: DNS (port 53), time service (port 37) Trivial File Transfer Protocol (TFTP) (port 69) Terminal Access Control Access Control System (TACACS) service (port 49) NetBIOS name server (port 137) NetBIOS datagram server (port 138) Boot Protocol (DHCP/BootP) client and server datagrams (ports 67 and 68) IEN-116 name service (port 42) Reference: Understanding and Troubleshooting DHCP in Catalyst Switch or Enterprise Networks

Correct Answer: Section: (none) Explanation
Which administrative distance is given to EIGRP summary routes?
A. 0
B. 1
C. 5
D. 90
E. 95
F. 150

Correct Answer: C Section: (none) Explanation
The following table displays the default AD for all routing protocols:

If there is a route to the subnet learned via RIP and a route to the subnet learned via STATIC, which route would be preferred to reach the destination address
A. The route learned via RIP will be used because its prefix has the longest match.
B. RIP has an administrative distance of 120, and static routes have an administrative distance of 1, so the static route would be preferred.
C. The static route to will be preferred because static routes have an administrative distance of 0 and the static route looks as though it is directly connected.
D. A show ip route to the destination will show that the destination is learned from both RIP and the static route, so the traffic to will be load balanced between the two paths.
E. The information given is not sufficient to determine this.

Correct Answer: A Section: (none) Explanation
Explanation: The longest match rule always takes precedence over any other routing information. The administrative distance (AD) values are only compared for destinations with subnet masks of eual length.

You are determining the routing protocol to use throughout your network. In doing this you compare the advantages of classless and classful protocols. Which of the following statements are true regarding classless routing protocols?
A. A default gateway is reuired.
B. Variable-length subnet masks are not supported.
C. Routers are automatically summarized to class boundaries.
D. Networks with different subnet masks can exist in the same address class.
E. All of the above

Correct Answer: D Section: (none) Explanation
Classless routing protocols understand that different routes within a major network can have different
masks. They include VLSM information in the routing updates, enabling the use of different subnet mask

Incorrect Answers:

A. There is no reuirement for a default gateway.
B. Classless routing protocols advertise the routing mask for each route. This enables VLSM (variable length subnet masks) support.
C. With classless routing the summarization process can manually controlled and can be invoked at any point within the network. It is not limited to class boundaries.

Which two of the following describe advantages of implementing a classless routing protocol, when compared to a classful routing protocol?
A. Support for VLSM.
B. Support for FLSM.
C. Summarization of discontinuous subnets.
D. Auto-summarization across network boundaries.
E. The ip classless command improves convergence time.

Correct Answer: AC Section: (none) Explanation
A. Classless routing protocols support VLSM, and that, in turn, leads to more efficient
allocation of subnet masks to meet different host reuirements on different subnetworks,
resulting in better utilization of host addresses.

C. Because subnets routes are propagated throughout the routing domain, summarization is
often reuired to keep the routing tables at a manageable size.
Incorrect Answers:
B, D: Fixed Length Subnet Masks (FLSM) and auto-summarized routes across network
boundaries are functions of classful routing protocols, not classless.

E. The convergence time of a network is due to numerous factors, including the timers of the routing
protocol, as well as support for triggered updates. The “ip classless” command has no impact on the
convergence time of any network.
Reference: Building Scalable Cisco Networks (Cisco Press) page 19-20.

You wish to use a classless IP routing protocol within your network. Which of the following classless routing protocols could you use? (Select all that apply)
C. RIPv1

Correct Answer: Section: (none) Explanation
A. D, E
Intermediate System to Intermediate System (IS-IS), Open Shortest Path First (OSPF) and
Enhanced IGRP are all classless routing protocols.
Note: RIPv2 and BGP are also classless routing protocols.
Incorrect Answers:

B, C: IGRP and RIPv1 are not classless. Both of these protocols do not support VLSM networks.
The Certkiller network administrator is considering using a link state routing protocol to replace their existing distance vector protocol. Which if the following are true regarding link state routing protocols?
A. Link-state protocols do not support summarization.
B. Static routes must be used to accommodate link redundancy.
C. All routers in the area know when another router joins the area.
D. Link-state protocols utilize spanning tree to propagate routing changes.
E. The spanning tree protocol must be enabled for link state protocols to work.

Correct Answer: C Section: (none) Explanation
All routers within an area will have the same view of the area, meaning they will all have the same topology
table. All of them will know when another router joins the area, since the routing topology table of all
routers in any area must remain identical.

Incorrect Answers

A: Link state protocols support route summarization, as well as variable length subnet masking.
B: Link redundancy does not reuire the use of static routes. Redundant links can be used with link state protocols, and load balancing over redundant links is also supported. D, E: The spanning tree is not to propagate routing changes. Instead it used to find the shortest path to the destinations. The spanning tree protocol is used at layer 2 to determine bridging and switching loops, not routing loops.
IS-IS and OSPF are two examples of link state routing protocols. Regarding the operation of link state protocols, which of the following are true?
A. Link state protocols periodically multicast the Link State Advertisements at 90 second intervals.
B. Link state routing protocols use Hello packets to build the link state database.
C. Link state routing protocols use poison reverse and holddown timer to prevent routing loops.
D. Link state routing protocols use Link State Advertisements to announce route changes.
E. All of the above

Correct Answer: D Section: (none) Explanation
Explanation: LSA – Link State Announcement. Used by OSPF, an LSA is used to announce changes in network topology to adjacent routers Each router periodically sends an LSA to provide information on a router’s adjacencies or to inform others when a router’s state changes. By comparing established adjacencies to link states, failed routers can be detected quickly and the network’s topology altered appropriately. From the topological database generated from LSAs, each router calculates a shortest-path tree, with itself as root. The shortest-path tree, in turn, yields a routing table.
Incorrect Answers:
A: Although link state protocols use multicasts for routing updates, they are sent using hellos. OSPF uses multicast IP addresses and LSAs are not sent every 90 seconds.
B: The Hello Protocol is responsible for establishing and maintaining neighbor relationships. It is used to build the neighbor table, not the link state database.
C: These are loop avoidance mechanisms used by distance vector routing protocols, not link state.
One of the serial links in an OSPF network is experiencing problems and continuously changes from up to down. In a link-state environment, what does the router do when a route flaps?
A. It enters the exstart state with its neighbors.
B. It floods the area with new routing information.
C. It generates a routing exchange using the hello protocol.
D. It waits for the holdown timers to expire and then sends an update.

Correct Answer: B Section: (none) Explanation
Explanation: One of the drawbacks of using OSPF is that it can be prone to issues resulting in flapping routes. OSPF is a very strong protocol in terms of convergence time-each router is aware of the entire topology in the area. This results in fast convergence. However, if a link flaps, or changes between up and down status uickly, a flood of LSAs may be generated. This may prevent the routers in the network from converging. Administrators may use the “spf holdtime” command to force OSPF into a waiting state before computing a new route.
You are an administrator of a network segment that uses RIP v2 as the routing protocol. How would the core router react if it were to detect a flapping link to a neighboring router?
A. It recalculates the network topology.
B. It purges that link from its routing table.
C. It places a hold-down on the routes from that link.
D. It sends a LSA to other router reuesting an RIP update.

Correct Answer: C Section: (none) Explanation
RIP is a distance vector routing protocol, which utilizes hold down timers and the rule of split horizons.
The purpose of the hold-down state is to ensure the validity of any new routes for the same destination.
Incorrect Answers:

A: RIP does not calculate a network topology.
B: This would not serve any practical purpose, since the purged link would then reappear. The link would be placed in a held state, but not purged.
D: OSPF utilizes link state advertisements (LSAs), but RIP routers do not.
Which of the following routing protocols listed below use the Class D address of to multicast its routing updates?
D. RIPv2

Correct Answer: D Section: (none) Explanation
Explanation: Class D addresses are multicast addresses used by many routing protocols for updating all neighbors on a link. Some of the Class D multicast addresses used by routing protocols are as follows: OSPF – and Routing Information Protocol version 2 (RIPSv2) – EIGRP – Reference: Building Scalable Cisco Networks (Cisco Press)
When comparing and contrasting the differences between classless and classful routing protocols, which of the following is true?
A. In a classful system, a router uses a bit mask to determine the network and host portions of an address and there is no class restriction.
B. In a classless system, a router determines the class of an address and then identifies the network and host octets based on that class.
C. In a classful system, subnet mask information is maintained and passed along with each routing update.
D. In a classless system, when a routing update is received about a different major network as configured on the receiving interface, the default subnet mask is applied.
E. In a classful system, when a routing update is received about the same major network as configured on the receiving interface, the router applies the subnet mask configured on the receiving interface.

Correct Answer: E Section: (none) Explanation
Explanation: Routing protocols can be divided into various categories, such as classful or classless, and distance-vector or link-state. A classful routing protocol is one that exchanges routing information based on the classful IP boundaries. A router running a classful routing protocol such as RIPv1 or IGRP that receives an update for a network to which it is not physically connected will summarize that network at the default classful boundary. If the router received a route to network, for instance, it would summarize the route to in its routing table, because an 8-bit ( subnet mask is the default classful boundary for Class A addresses. A classless routing protocol, such as RIPv2, OSPF or EIGRP, exchanges the subnet mask with the subnet information. So if the aforementioned router was running OSPF, it would receive a route to network with a 24-bit ( subnet mask included, and would not summarize the route to
Which two statements are true with regard to RIPv1 and OSPF? (Choose two)
A. RIPv1 uses the Dijkstra algorithm while OSPF uses the Bellman-Ford algorithm for calculating best path.
B. RIPv1 uses the Bellman-Ford algorithm, OSPF uses the Dijkstra algorithm for calculating best path.
C. RIP forwards the entire routing table incrementally, OSPF link-state advertisements are sent out when a change occurs and every thirty minutes if no change occurs.
D. RIPv1 maintains a 15 hop count limit while OSPF maintains a 255 hop count limit.
E. Both RIPv1 and OSPF carry subnet mask information and therefore support VLSM.

Correct Answer: BC Section: (none) Explanation
Explanation: RIP is a distance vector routing protocol, which uses the Bellman-Ford algorithm for calculating the best path to a destination. OSPF is a link state routing protocol, which means that it uses the Dijkstra algorithm to determine the best path. RIP also periodically advertises the entire routing protocol to all neighbors, while OSPF uses LSA information to flood the area with routing information, but only after a topology change has occurred. To maintain stability, OSPF also floods out the entire OSPF table every thirty minutes if no change has occurred. Incorrect Answers:
A: The reverse is true.
D: RIP maintains a hop limit of 15 (16 means it is unreachable) but OSPF does not have any hop limitations.
E: RIPv1 does not carry the subnet mask information in the routing updates, and so it does not support VLSM. RIPv2 does, however.
The Certkiller IGRP network is displayed in the diagram below:

Certkiller 1 and Certkiller 2 are running IGRP. Certkiller 1 receives an update on its Fa0/0 interface from Certkiller 2 about the network. Which mask will be applied to the update?

Correct Answer: A Section: (none) Explanation
Explanation: The ability to specify a different subnet mask for the same network number on different subnets is called Variable-Length Subnet Mask (VLSM). RIPv1 and IGRP are classful protocols and are incapable of carrying subnet mask information in their updates. Before RIPv1 or IGRP sends out an update, it performs a check against the subnet mask of the network that is about to be advertised and, in case of VLSM, the subnet gets dropped. In this example, first router Certkiller 2 checks to see whether is part of the same major net as, which is the network assigned to the interface that will be sourcing the update. It is not, and so Certkiller 2 will summarize at the network boundary, which is since this is a class C network.
You’re a systems administrator who’s just chosen OSPF over RIP version 1. Your junior administrator Britney is confused and asks you why you didn’t choose RIP. What would you tell her? (Choose all that apply)
A. OSPF maintains smaller routing tables than RIP
B. OSPF cost metric is based on number of hops.
C. OSPF only sends routing updates only when necessary.
D. OSPF supports VLSM and allows more efficient use of IP addresses.

Correct Answer: CD Section: (none) Explanation
Explanation: C: RIP use periodic broadcast of the entire routing table, while OSPF use event-triggered announcements. OSPF uses
D: RIP Version 1 does not support VLSM, while OSPF does. Incorrect Answers:
A: The size of the routing table depends on the number of routes. Since RIP version 1 automatically summarizes at the network boundary, the routing tables of RIP networks are generally smaller than OSPF networks.
B: RIP uses hop as cost metric. OSPF uses a metric based on the bandwidth of the links to the destination.

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