ICND2 – IP Routing

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Question 1

[am4show have=’p2;’]Which two are advantages of static routing when compared to dynamic routing? (choose two)

A. Security increases because only the network administrator may change the routing tables.
B. Configuration complexity decreases as network size increases.
C. Routing updates are automatically sent to neighbors.
D. Route summarization is computed automatically by the router.
E. Routing traffic load is reduced when used in stub network links.
F. An efficient algorithm is used to build routing tables using automatic updates.
G. Routing tables adapt automatically to topology changes.

 

Answer: A E[/am4show]

Explanation

Static routing can only be configured for each route manually so it is more secure than dynamic routing which only needs to declare which networks to run -> A is correct.

Also static route does not use any complex algorithm to find out the best path so no routing updates need to be sent out -> reduce routing traffic load. Static routing is useful especially in stub network links.

Note: Stub network (or stub router) is used to describe a network (or router) that does not have any information about other networks except a default route. This type of network (or router) usually has only one connection to the outside.

Question 2

[am4show have=’p2;’]Which parameter would you tune to affect the selection of a static route as a backup, when a dynamic protocol is also being used?

A. hop count
B. administrative distance
C. link bandwidth
D. link delay
E. link cost

 

Answer: B[/am4show]

Explanation

By default a static route has the Administrative Distance (AD) of 1, which is always preferred to dynamic routing protocols. In some cases we may want to use dynamic routing protocols and set static routes as a backup route when the “dynamic” routes fail -> we can increase the AD of that static route to a higher value than the AD of the dynamic routing protocols.

Question 3

[am4show have=’p2;’]Which statement is true, as relates to classful or classless routing?

A. RIPV1 and OSPF are classless routing protocols.
B. Classful routing protocols send the subnet mask in routing updates.
C. Automatic summarization at classful boundaries can cause problems on discontigous networks.
D. EIGRP and OSPF are classful routing protocols and summarize routes by default.

 

Answer: C[/am4show]

Explanation

Discontiguous networks are networks that have subnets of a major network separated by a different major network. Below is an example of discontiguous networks where subnets 10.10.1.0/24 and 10.10.2.0/24 are separated by a 2.0.0.0/8 network.

If we configure automatic summarization at classful boundaries, users on network 10.10.1.0/24 cannot communicate with users on network 10.10.2.0/24.

If you are not clear about automatic summarization please read the last part of this tutorial: http://www.9tut.com/eigrp-routing-protocol-tutorial.

Question 4

[am4show have=’p2;’]A technician pastes the configurations in the exhibit into the two new routers shown. Otherwise, the routers are configured with their default configurations. A ping from Host1 to Host2 fails, but the technician is able to ping the S0/0 interface of R2 from Host1. The configurations of the hosts have been verified as correct. What is the cause of the problem?

A. The serial cable on R1 needs to be replaced.
B. The interfaces on R2 are not configured properly.
C. R1 has no route to the 192.168.1.128 network.
D. The IP addressing scheme has overlapping subnetworks.
E. The ip subnet-zero command must be configured on both routers.

 

Answer: C[/am4show]

Explanation

Host1 can ping the Serial interface of R2 because R1 has the network of 192.168.1.4/30 as directly connected route. But R1 does not know how to route to the network of Host2 (192.168.1.128/26) so R1 will drop that ping without trying to send it out S0/0 interface. To make the ping work, we have to configure a route pointing to that network (for example: ip route 192.168.1.128 255.255.255.192 s0/0 on R1).

Question 5

[am4show have=’p2;’]Refer to the exhibit. The Lakeside Company has the internetwork in the exhibit. The Administrator would like to reduce the size of the routing table to the Central Router. Which partial routing table entry in the Central router represents a route summary that represents the LANs in Phoenix but no additional subnets?

A – 10.0.0.0 /22 is subnetted, 1 subnet
D 10.0.0.0 [90/20514560] via 10.2.0.2 6w0d, serial 0/1

B – 10.0.0.0 /28 is subnetted, 1 subnet
D 10.2.0.0 [90/20514560] via 10.2.0.2 6w0d, serial 0/1

C – 10.0.0.0 /30 is subnetted, 1 subnet
D 10.2.2.0 [90/20514560] via 10.2.0.2 6w0d, serial 0/1

D – 10.0.0.0 /22 is subnetted, 1 subnet
D 10.4.0.0 [90/20514560] via 10.2.0.2 6w0d, serial 0/1

E – 10.0.0.0 /28 is subnetted, 1 subnet
D 10.4.4.0 [90/20514560] via 10.2.0.2 6w0d, serial 0/1

F – 10.0.0.0 /30 is subnetted, 1 subnet
D 10.4.4.4 [90/20514560] via 10.2.0.2 6w0d, serial 0/1

 

Answer: D[/am4show]

Explanation

All the above networks can be summarized to 10.0.0.0 network but the question requires to “represent the LANs in Phoenix but no additional subnets” so we must summarized to 10.4.0.0 network. The Phoenix router has 4 subnets so we need to “move left” 2 bits of “/24”-> /22 is the best choice -> D is correct.

Question 6

[am4show have=’p2;’]Refer to the exhibit. How will the router handle a packet destined for 192.0.2.156?

A. The router will drop the packet.
B. The router will return the packet to its source.
C. The router will forward the packet via Serial2.
D. The router will forward the packet via either Serial0 or Serial1.

 

Answer: C[/am4show]

Explanation

From the output we see a line “Gateway of last resort is 192.168.4.1 to network 0.0.0.0”. Gateway of last resort refers to the next-hop router of a router’s current default route. Therefore all the traffic through this router to destination networks not matching any other networks or subnets in the routing table will be sent to 192.168.4.1 (which is on Serial2) -> packet destined for 192.0.2.156 (or an unknown destination) will be forwarded via Serial2.

An weird thing in the output above is the missing of the asterisk mask (*) which represents for the candidate default route. To set the “Gateway of last resort is 192.168.4.1 to network 0.0.0.0” as the output above we can use these commands:

ip route 0.0.0.0 0.0.0.0 192.168.4.1
ip default-network 192.168.4.0

But these commands will create an static routing in the routing table with an asterisk mask. Maybe the output shown above is missing that route.

For more information about the command ip default-network please visit: http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094374.shtml.

Question 7

[am4show have=’p2;’]Refer to the exhibit. RTA is configured with a basic configuration. The link between the two routers is operational and no routing protocols are configured on either router. The line shown in the exhibit is then added to router RTA. Should interface Fa0/0 on router RTB shut down, what effect will the shutdown have on router RTA?

A. A route to 172.16.14.0/24 will remain in the RTA routing table.
B. A packet to host 172.16.14.225 will be dropped by router RTA
C. Router RTA will send an ICMP packet to attempt to verify the route.
D. Because router RTB will send a poison reverse packet to router RTA, RTA will remove the route.

 

Answer: A[/am4show]

Explanation

Static routes remain in the routing table even if the specified gateway becomes unavailable. If the specified gateway becomes unavailable, you need to remove the static route from the routing table manually. However, static routes are removed from the routing table if the specified interface goes down, and are reinstated when the interface comes back up.

Therefore the static route will only be removed from the routing table if the S0/0 interface on RTA is shutdown.

(Reference: http://www.cisco.com/en/US/docs/security/asa/asa84/configuration/guide/route_static.html)