Module 14 Routing Concepts

Refer to the exhibit. What will the router do with a packet that has a destination IP address of 192.168.12.227?

• Drop the packet.

• Send the packet out the Serial0/0/0 interface.

• Send the packet out the GigabitEthernet0/0 interface.

• Send the packet out the GigabitEthernet0/1 interface.

Answer explanation

After a router determines the destination network by ANDing the destination IP address with the subnet mask, the router examines the routing table for the resulting destination network number. When a match is found, the packet is sent to the interface associated with the network number. When no routing table entry is found for the particular network, the default gateway or gateway of last resort (if configured or known) is used. If there is no gateway of last resort, the packet is dropped. In this instance, the 192.168.12.224 network is not found in the routing table and the router uses the gateway of last resort. The gateway of last resort is the IP address of 209.165.200.226. The router knows this is an IP address that is associated with the 209.165.200.224 network. The router then proceeds to transmit the packet out the Serial0/0/0 interface, or the interface that is associated with 209.165.200.224.

Refer to the exhibit. PC A sends a request to Server B. What IPv4 address is used in the destination field in the packet as the packet leaves PC A?

• 192.168.10.10

• 192.168.11.1

• 192.168.10.1

• 192.168.12.16

Answer explanation

The destination IP address in packets does not change along the path between the source and destination.

Refer to the exhibit.What does R1 use as the MAC address of the destination when constructing the frame that will go from R1 to Server B?

• If the destination MAC address that corresponds to the IPv4 address is not in the ARP cache, R1 sends an ARP request.

• The packet is encapsulated into a PPP frame, and R1 adds the PPP destination address to the frame.

• R1 uses the destination MAC address of S1.

• R1 leaves the field blank and forwards the data to the PC.

Answer explanation

Communication inside a local network uses Address Resolution Protocol to obtain a MAC address from a known IPv4 address. A MAC address is needed to construct the frame in which the packet is encapsulated.

What are two advantages of static routing over dynamic routing? (Choose two.)

• Static routing is more secure because it does not advertise over the network.

• Static routing scales well with expanding networks.

• Static routing requires very little knowledge of the network for correct implementation.

• Static routing uses fewer router resources than dynamic routing.

• Static routing is relatively easy to configure for large networks.

Answer explanation

Static routing requires a thorough understanding of the entire network for proper implementation. It can be prone to errors and does not scale well for large networks. Static routing uses fewer router resources, because no computing is required for updating routes. Static routing can also be more secure because it does not advertise over the network.

What happens to a static route entry in a routing table when the outgoing interface associated with that route goes into the down state?

• The static route is removed from the routing table.

• The router polls neighbors for a replacement route.

• The static route remains in the table because it was defined as static.

• The router automatically redirects the static route to use another interface.

Answer explanation

When the interface associated with a static route goes down, the router will remove the route because it is no longer valid.

What is a characteristic of a static route that matches all packets?

• It backs up a route already discovered by a dynamic routing protocol.

• It uses a single network address to send multiple static routes to one destination address.

• It identifies the gateway IP address to which the router sends all IP packets for which it does not have a learned or static route.

• It is configured with a higher administrative distance than the original dynamic routing protocol has.

Answer explanation

A default static route is a route that matches all packets. It identifies the gateway IP address to which the router sends all IP packets for which it does not have a learned or static route. A default static route is simply a static route with 0.0.0.0/0 as the destination IPv4 address. Configuring a default static route creates a gateway of last resort.

What route would have the lowest administrative distance?

• a directly connected network

• a static route

• a route received through the EIGRP routing protocol

• a route received through the OSPF routing protocol

Answer explanation

The most believable route or the route with the lowest administrative distance is one that is directly connected to a router.

When would it be more beneficial to use a dynamic routing protocol instead of static routing?

• in an organization with a smaller network that is not expected to grow in size

• on a stub network that has a single exit point

• in an organization where routers suffer from performance issues

• on a network where there is a lot of topology changes

Answer explanation

Dynamic routing protocols consume more router resources, are suitable for larger networks, and are more useful on networks that are growing and changing.

Which route would be used to forward a packet with a source IP address of 192.168.10.1 and a destination IP address of 10.1.1.1?

• C 192.168.10.0/30 is directly connected, GigabitEthernet0/1

• S 10.1.0.0/16 is directly connected, GigabitEthernet0/0

• O 10.1.1.0/24 [110/65] via 192.168.200.2, 00:01:20, Serial0/1/0

• S* 0.0.0.0/0 [1/0] via 172.16.1.1

Answer explanation

Even though OSPF has a higher administrative distance value (less trustworthy), the best match is the route in the routing table that has the most number of far left matching bits.

Refer to the exhibit. What is the administrative distance value of the route for router R1 to reach the destination IPv6 address of 2001:DB8:CAFE:4::A?

• 1

• 4

• 110

• 120

Answer explanation

The RIP route with the source code R is used to forward data to the destination IPv6 address of 2001:DB8:CAFE:4::A. This route has an AD value of 120.