Chapter 18 - Configuring IPv4 Addresses and Static Routes Flashcards
A PC user opens a command prompt and uses the ipconfig command to see that the PC’s IP address and mask are 192.168.4.77 and 255.255.255.224. The user then runs a test using the ping 192.168.4.117 command. Which of the following answers is the most likely to happen?
a. The PC sends packets directly to the host with address 192.168.4.117.
b. The PC sends packets to its default gateway.
c. The PC sends a DNS query for 192.168.4.117.
d. The PC sends an ARP looking for the MAC address of the DHCP server.
B. PCs use two-option logic: send local packets (destined for hosts in the same subnet) directly, and send remote packets (destined for hosts in other subnets) to the default gateway/router. In this case, the PC’s own IP address is 192.168.4.77, with mask 255.255.255.224, so it is in subnet 192.168.4.64/27. This subnet has a range of addresses from 192.168.4.64 to 192.168.4.95, including the subnet and broadcast addresses. As a result, the PC sends the packet to its default gateway. As for the other incorrect answers, if the ping command had used a hostname, it would have first asked a DNS server to resolve the name. Also, the PC already has an IP address, so DHCP would not be needed.
Router R1 lists a route in its routing table. Which of the following answers list a fact from a route that the router then compares to the packet’s destination address? (Choose two answers.)
a. Mask
b. Next-hop router
c. Subnet ID
d. Outgoing interface
A and C. The route defines the group of addresses represented by the route using the subnet ID and mask. The router can use those numbers to find the range of addresses that should be matched by this route. The other two answers list facts useful when forwarding packets that happen to match the route.
Router 1 has a Fast Ethernet interface 0/0 with IP address 10.1.1.1. The interface is connected to a switch. This connection is then migrated to use 802.1Q trunking. Which of the following commands could be part of a valid configuration for Router 1’s Fa0/0 interface? (Choose two answers.)
a. interface fastethernet 0/0.4
b. dot1q enable
c. dot1q enable 4
d. trunking enable
e. trunking enable 4
f. encapsulation dot1q 4
A and F. Of all the commands listed, only the two correct answers are syntactically correct router configuration commands. The command to enable 802.1Q trunking is encapsulation dot1q vlan_id.
A Layer 3 switch has been configured to route IP packets between VLANs 1, 2, and 3, which connect to subnets 172.20.1.0/25, 172.20.2.0/25, and 172.20.3.0/25, respectively. The engineer issues a show ip route command on the Layer 3 switch, listing the connected routes. Which of the following answers lists a piece of information that should be in at least one of the routes?
a. Interface Gigabit Ethernet 0/0.3
b. Next-hop router 172.20.4.1
c. Interface VLAN 2
d. Mask 255.255.255.0
C. The configuration of the Layer 3 switch’s routing feature uses VLAN interfaces, with the interface number matching the VLAN ID. The matching connected routes, like all connected IP routes, will list the interfaces but not a next-hop IP address. The three connected routes will list the VLAN interfaces 1, 2, and 3, respectively.
An engineer configures a static IPv4 route on Router R1. Which of the following pieces of information should not be listed as a parameter in the configuration command that creates this static IPv4 route?
a. The destination subnet’s subnet ID
b. The next-hop router’s IP address
c. The next-hop router’s neighboring interface
d. The subnet mask
C. The ip route command can refer to the IP address of the next-hop router or to the local router’s interface. It also refers to the subnet ID and matching subnet mask, defining the range of addresses matched by the route.
Which of the following commands correctly configures a static route?
a. ip route 10.1.3.0 255.255.255.0 10.1.130.253
b. ip route 10.1.3.0 serial 0
c. ip route 10.1.3.0 /24 10.1.130.253
d. ip route 10.1.3.0 /24 serial 0
A. The correct syntax lists a subnet number, then a subnet mask in dotted-decimal form, and then either an outgoing interface or a next-hop IP address.
A network engineer configures the ip route 10.1.1.0 255.255.255.0 s0/0/0 command on a router, and then issues a show ip route command from enable mode. No routes for subnet 10.1.1.0/24 appear in the output. Which of the following could be true?
a. The ip route command has incorrect syntax and was rejected in config mode.
b. interface s0/0/0 is down.
c. The router has no up/up interfaces in Class A network 10.0.0.0.
d. The ip route command is missing a next-hop router IP address.
B. The ip route command can reference an outgoing interface or a next-hop IP address, which rules out one answer. The command does use the correct syntax, ruling out another answer. There is no requirement for a router to have any particular interface IP addresses in relation to the configuration of an ip route command, ruling out yet another answer.
The checks that IOS uses when looking at a new ip route command include whether the outgoing interface is up/up, whether the next-hop address is reachable, and, if there is a competing route from another source, whether the other route has a better administrative distance.
