CCNA 2 Chapter 4

Which of these have volatile memory? RAM, ROM, NVRAM, or Flash?


What is saved in RAM on a router?

running IOS
running configuration file
IP routing and ARP tables
packet buffer

What is saved in ROM on a router?

bootup instructions
basic diagnostic software
limited IOS

What is saved in NVRAM on a router?

startup configuration file

What is saved in Flash memory on a router?

other system files

What code is used in the routing table to identify routes learned through EIGRP?


What 3 steps does a router do when it receives a packet destined for another network?

Step 1: de-encapsulates the Layer 3 packet by removing Layer 2 frame header and trailer
Step 2: examines destination IP address of the packet to find the best path in the routing table
Step 3: encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface

What address and prefix length is used when configuring an IPv6 default static route?


When a router learns that multiple paths are available to a destination network from the same routing protocol, which factor is considered by a router to choose the best path to forward a packet?

the lowest metric

Describe 3 features of Cisco devices that perform routing:

1. The IP address of a LAN interface on a Layer 3 device provides the default gateway for hosts connected to that LAN.
2. A routing table is automatically created for directly connected, active LAN and WAN interfaces.
3. Routing tables are volatile. When power is removed from a Layer 3 device, the routing table ceases to exist.

Why are routers needed in networking?

to forward network traffic to remote networks - each interface on a router belongs to a different network

What are 3 functions of the transport layer?

packet delivery
packet delivery status

What are 2 components of a router?

1. ROM contains diagnostics executed on hardware modules.
2. Flash memory does not lose its contents during a reboot.

What is a gateway of last resort?

the IP address of another router - a default route

Which 2 tasks can be accomplished by using the command history feature?

1. Set the command history buffer size.
2. Recall previously entered commands.

During the process of encapsulation, how does the PC determine if the packet is destined for a host on a remote network?

by performing the AND operation on the destination IP address and its own subnet mask

Which 2 statements describe characteristics of load balancing?

1. Load balancing allows a router to forward packets over multiple paths to the same destination network.
2. Unequal cost load balancing is supported by EIGRP.

What is the purpose of a routing protocol?

It allows a router to share information about known networks with other routers.

Which 2 statements describe static routes?

1. They require manual reconfiguration to accommodate network changes.
2. They are identified in the routing table with the prefix S

The output of the show ip route command contains the following:
S [1/0] via
What value is indicated by the 1 in the [1/0] portion of the output?

administrative distance

Router Bootup Process:

2. Bootstrap - ROM
3. Load IOS from Flash Memory
4. Load Startup-Config from NVRAM

What is meant by administrative distance (AD)?

The trustworthiness of the route source - a lower value indicates preferred route source. Cisco IOS uses AD.

Would R1 install an EIGRP route or a RIP route?

EIGRP - because adminisitrative distance of EIGRP (90) is lower than RIP (120)

Which command would you issue to see if load balancing is in effect on a router?

show ip route

List 2 facts about EIGRP:

* only EIGRP supports unequal cost load balancing
* chooses a path based on its composite metric

Which metric does RIP (routing information protocol) use?

hop count

Which metric does OSPF (open shortest path first)?

cost based on bandwidth (cumulative from source to destination)

Which metric does EIGRP use?


What are 3 benefits of using static routes?

* improved security
* the admin maintains control over routing
* use less bandwidth

The following line of code is displayed in a routing table:
R [120/2] via, 00:00:16, S0/0/0
What can be concluded?

The value 120 is used to determine the best path when a router has more than one routing protocol configured for the same destination network

The following line of code is present in the routing table:
O [110/129] via, 00:00:05, Serial0/0/1
What does the number 129 indicate in this output?

The cost for this link has a value of 129.

The network admin decided to convert the static network 0f 30 routers to dynamic routing. What characteristics of protocols should be considered in this selection process?

OSPF can be used between the routers.

A router learns two paths with equal metrics to a destination network via the RIP routing protocol. How will the router handle packets to the destination network?

The router will install both routes in the routing table and load balance between the two.

When multiple routing protocols have a route to the same destination network, what determines which route is installed in the routing table?

lowest administrative distance

What does MTBF stand for?

mean time between failures

Describe process switching:

* old & slow
* When each & every packet arrives on an interface, it is forwarded to the CPU which determines the exit interface and forwards the packet

Describe fast switching:

uses a fast-switching cache to store next-hop info so next packet going to the same destination is reused without CPU intervention

Describe CEF (Cisco Express Forwarding):

* fastest - preferred Cisco method
* builds FIB & change triggered adjacency table for next hop interface, so when a network converges the router can forward a packet

What happens when a router is configured with the ipv6 unicast-routing command.

Router interface sends ICMPv6 router advertisement messages, which enables a connected PC to auto configure an IPv6 address and set a default gateway without using a DHCPv6 server.

What is dual stacking?

Assigning both an IPv6 and IPv4 address on an interface.

What is a loopback interface?

* a logical internal router interface - if the router is functioning, it is always UP
* a router uses the loopback interface address for identification, rather than an IP address assigned to a physical port which is useful for OSPF

show ip interface brief
show ip route
show running-config interface
show interfaces
show ip interface

summary for all interfaces
routing table stored in RAM
displays commands configured
displays interface info & packet flow count
displays IPv4 info for all interfaces

What is the output for command show ipv6 interface brief?

interface status, link local, global unicast &
multicast address

What does a | (pipe) symbol do?

filters show commands

What does "switching function" refer to for a router?

a router accepts a packet on one interface and forwards it out of another interface

What steps does a router take with a packet received from one network and destined for another network?

1 - de-encapsulates the Layer 3 packet (removes Layer 2 frame header & trailer
2 - examines destination IP address of the IP packet & finds best path in routing table
3 - encapsulates Layer 3 packet into new Layer 2 frame & forwards it out exit interface

What has a Layer 3 IPv4 address?

devices - as a packet travels from source to final destination, Layer 3 IP addresses don't change

What has layer 2 data link addresses?

Ethernet interfaces - Layer 2 data link addresses change at every hop as the packet is de-encapsulated and re-encapsulated in a new frame by each router.

Can a packet be encapsulated in a different type of Layer 2 frame than the one in which it was received?


What happens when PC1 sends a packet to PC2 in its own network?

PC1 refers to its ARP cache for the MAC address of the device with that destination IPv4 address. If it does not find the MAC address, PC1 generates an ARP request.

What happens when PC1 sends a packet to PC3 in a remote network?

PC1 checks its ARP cache for the IPv4 address of the default gateway. If it does not find the default gateway, PC1 sends an ARP request.

What does IPv6 use instead of ARP?

ICMPv6 Neighbor Solicitation & Neighbor Advertisement messages and the table is called the neighbor cache

The routing table search results in 1 of 3 path determinations, which are?

* directly connected network - packet forwarded to destination device
* remote network - packet forwarded to next router
* no route determined - packet forwarded to Gateway of Last Resort (if there is a default route) or packet discarded (if there isn't a default route - ICMP unreachable message sent to source IP address)

What is equal cost load balancing?

when a router has 2 or more paths to a destination with equal cost metrics it forwards packets using both paths equally

List the AD for route sources:

Connected = 0
Static = 1
EIGRP = 90
OSPF = 110
RIP = 120

Which codes identifies how the network was learned by the router?

L - router interface address
C - directly connected address
S - static route
D - dynamically learned from another router using EIGRP
O - dynamically learned from another router using OSPF

Where is the routing tabled stored?

data file in RAM

To enable IPv6 routers to forward traffic, what must you configure?

ipv6 unicast-routing command

What do routers do during network discovery?

routers exchange routes and update their routing tables

What does a routing table contain for directly connected interfaces?

route source, destination network, outgoing interface

What happens if a router is running a dynamic routing protocol?

makes a best path determination to a network and also determines a new best path if the initial path becomes unusable

REMOTE Network Routing Table