Notes – Odom, Chapter 14 Routing Protocol Concepts and ...

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Susan
Ferdon


Notes

Odom, Chapter 14

Routing Protocol Concepts and Configuration

Flashcards Set:

http://www.flashcardmachine.com/1335840/i84t



network route

A data transmission path through one or more networks
between two end nodes.

route metrics

The cost in time and res
ources to send a data packet
over that route.

s
tatic route

A route that is manually configured on a router. Includes
destination IP, subnet mask, and next
-
hop
-
IP (or
outgoing interface). Route remains static/unchanged
unless reconfigured.

d
efault route

O
n a router, the route that is considered to match all
packets that are not otherwise matched by some more
specific route.

d
ynamic route

A route that the router learns from neighboring routers.

r
outing
protocol

A set of messages and processes with which r
outers can
exchange information about routes to reach subnets in a
particular network. Examples of routing protocols include
the Enhanced Interior Gateway Routing Protocol (EIGRP),
the Open Shortest Path First (OSPF) protocol, and the
Routing Information P
rotocol (RIP).

Routing Information Protocol

RIP

An Interior Gateway Protocol (IGP) that uses distance
vector logic and router hop count as the metric. RIP
Version 1 (RIP
-
1) has become unpopular, with RIP
Version 2 (RIP
-
2) providing more features, includ
ing
support for VLSM.

Enhanced Interior Gateway Router Protocol

EIGRP

EIGRP is an advanced distance
-
vector routing protocol,
with optimizations to minimize both the routing instability
incurred after topology changes, as well as the use of
bandwidth and processing power in the router. The data
EIGRP collects is stored in thr
ee tables: Neighbor Table,
Topology Table, and Routing table. Routing information is

exchanged only upon the establishment of new neighbor
adjacencies, after which only changes are sent
.

Open Shortest Path First

OS
PF

A
n adaptive routing protocol for Int
ernet Protocol (IP)
networks which
uses a link state routing algorithm
and

operates
within a single autonomous system (AS). It
gathers link state information from ava
ilable routers and
constructs a topology map of the network. The topology
determines the routing table presented to the Internet
Layer which makes routing decisions based solely on the
destination IP address found in IP packets.

Intermediate System to Intermediate System
Routing Protocol

IS
-
IS

An interior gateway protocol, designed for use within an
administrative domain or network. IS
-
IS is a link
-
state
routing protocol, operating by reliably flooding link state
information throughout a network of routers. Each IS
-
IS
router independently builds
a database of the network's
topology,
and
p
ackets (datagrams) are

forwarded, based
on the computed ideal
path, through the network to the
destination
.

a
dministrative
d
istance

In Cisco routers, a means for one router to choose
between multiple routes to reach the same subnet when
those routes were
learned by different routing protocols.
The lower the administrative distance, the better the
source of the routing information.

m
etric

A unit of measure used by routing protocol algorithms to
determine the best route for traffic to use to reach a
particu
lar destination.

Variable
-
length subnet masking

VLSM

The capability to specify a different subnet mask for the
same Class A, B, or C network number on different
subnets. VLSM
can
help optimize available address space.

Interior Gateway Protocol

IGP

A
routing protocol that was designed and intended for use
inside a single autonomous system
.

Exterior Gateway Protocol

EGP

A routing protocol that was designed and intended for use
between different autonomous systems
.

AS

Autonomous System


An internetw
ork in the administrative control of one
organization, company, or governmental agency, inside
which that organization typically runs an Interior Gateway
Protocol (IGP).

Border Gateway Protocol

BGP

A protocol that is used
to exchange routes between
rout
ers in different autonomous systems
. It is an EGP.

b
alanced hybrid

A term that refers to a general type of routing protocol
algorithm, the other two being distance vector and link
state. The Enhanced Interior Gateway Routing Protocol
(EIGRP) is the only r
outing protocol that Cisco classifies
as using a balanced hybrid algorithm.

c
lassful routing
protocol

Does not transmit the mask information along with the
subnet number, and therefore must consider Class A, B,
and C network boundaries and perform
autosum
marization at those boundaries. Does not
support VLSM.

c
lassless
routing
protocol

An inherent characteristic of a routing protocol,
specifically that the routing protocol does send subnet
masks in its routing updates, thereby removing any need
to make ass
umptions about the addresses in a particular
subnet or network, making it able to support VLSM and
manual route summarization.

c
onvergence

The time required for routing protocols to react to
changes in the network, removing bad routes and adding
new, bett
er routes so that the current best routes are in
all the routers’ routing tables.

d
istance vector

The logic behind the behavior of some interior routing
protocols, such as RIP. Distance vector routing algorithms
call for each router to send its entire rou
ting table in each
update, but only to its neighbors. Distance vector routing
algorithms can be prone to routing loops but are
computationally simpler than linkstate routing algorithms.

l
ink
-
state

A classification of the underlying algorithm used in some
routing protocols. Link
-
state protocols build a detailed
database that lists links (subnets) and their state (up,
down), from which the best routes can then be
calculated.

r
outing update

A generic reference to any routing protocol’s messages in
which it s
ends routing information to a neighbor.


CCNA Certification for Dummies
---
BEST!!


(The following is a combination of info from the textbook and Dummies
book.)


A
network route
is a data transmission path through one or more networks
between two end node
s. More than one route can exist. The main purpose of
a router is to find the best route to read a destination node. The best route
is calculated through
route metrics
: the cost in time and resources to send a
data packet over that route (Dummies, p. 593).


There are three types of network routes:



Static routes: Defined manually on a router

the
y
are static
(unchanged) unless you reconfigure.

o

Advantages:



Efficiency

you can leave routing protocols disabled which
saves bandwidth.



Security

you can filter
routing data using firewalls and
VPN to secure data no matter which path they travel on.

o

Disadvantages:



Maintenance

management overhead to update routes



Accuracy

if network changes and you don’t update static
routes you will have lost or delayed data.



Scalability

Large networks have hundreds or thousands
of alternate routes

too many to configure and maintain
statically.



Default routes:
Default routes are static routes that you define for
packets bound to a destination network that is not in any of
the
routing tables on your router. A default route is a data transmission
path to that default outbound gateway in a network.


o

Default routes work best when only one path exists to a part of
the network.


o

Without a default route, the router will discards p
ackets that
don’t match the routing table.



Dynamic routes:
Routes that change over time. May be due to network
topology and traffic updates, available bandwidth, and link state.

o

Advantages:



Low maintenance

routes are automatically updated, all
you have t
o do is configure routing protocols on your
routers.



Accuracy

Routing protocols keep track of network
changes which means routers will send packets over the
best possible routes.



Scalability


in a large network it’s a maintenance
nightmare to define all
routes statically. Routing protocols
allow routers to communicate about routes they know,
new routes they discover, and routes that become
unavailable or overloaded.

o

Disadvantages:



Overhead

consumes bandwidth because they regularly
send route update pac
kets between routers.





Connected and Static Routes

Connected Routes



A router adds routes to its routing table for the subnets connected to
each of the router’
s interfaces
-
the router must have an IP address
and mask configured on the interface
(staticall
y with the ip address command
or dynamically using Dynamic Host Configuration Protocol [DHCP])
and both
interface status codes must be “up.”



In Example 14
-
1, the output of the
show ip route
command confirms
that Albuquerque indeed added a route to all thre
e subnets to its
routing table.



The output begins with a single
-
letter code legend, with “C” meaning
“connected.”



The output lists the mask

in prefix notation by default.



In cases when one mask is used throughout a single classful network

in other words
, static
-
length subnet masking (SLSM) is used

the
show ip route command output lists the mask on a heading line above
the subnets o
f
that classful network.



Static Routes

http://ww
w.petri.co.il/csc_how_to_static_routes_cisco_ios.htm

http://ciscotests.org/ccna.php?part=6



Static routes are best for LANs

maintenance issues make static
routes practically impossible for WAN/large net
works. If a route
changes, that change would have to be manually
configured on each
individual
router.



Configure static routes using the
ip route
command in global
configuration mode. Syntax:

ip route

dest
-
ip

subnet
{
next
-
hop
-
ip
|
interface
}

o

Dest
-
ip
:
IP address of the destination network. You are
registering a static route to the destination network.

o

Subnet
: This is the subnet mask of the destination network;
defines which part of address is network and which is host.

o

{next
-
hop
|
interface
}: IP gatewa
y (router) through which you
reach the destination network. Specify the IP address of the next
hop or the outbound interface through which the router can
reach the destination.
Interface is used when it’s a point
-
to
-
point
serial link.

o

{} means
you must spe
cify something, | (pipe) means choose
one or the other of the options.



To remove a static route use the usual
no
prefix with
ip route

command
:
no ip route

dest
-
ip
[
subnet
] {
next
-
hop
-
ip
|
interface
}
.



You configure default routes using the same
ip route
comm
and in
global configuration mode. However, the IP address and subnet mask
are 0.0.0.0

which means “match all packets”
-

since the network is
unknown.



You can see all routes using
show ip route
command. To see only
statically configured routes, use
show i
p route static
.



Telnet to a router and use
ping
commands to see which routes
a
router is able to connect to
(
Text, p. 444).



When you troubleshoot this internetwork, you can use the extended
ping
command to act like you issued a ping from a computer on that

subnet, without having to call a user and ask to enter a ping command
for you on the PC.


Routing Protocol Overview

Routing protocols help routers learn routes by having each router advertise
the routes it knows. Each router begins by knowing only connect
ed routes.
Then, each router sends messages, defined by the routing protocol, that list
the routes. When a router hears a routing update message from another
router, the router hearing the update learns about the subnets and adds
routes to its routing tabl
e
(Text, p. 448).


Routing protocols exchange network, routes, and metric information
between routers to help find optimal routes as fast as possible. Routers use
the information provided by routing protocols to build their routing tables for
each routed p
rotocol to keep track of networks, paths to networks, and
metrics associated with each route (Dummies, p. 598).


The most widely used routing protocols are:



Routing Information Protocol (RIP)



Enhanced Interior Gateway Routing Protocol (EIGRP)



Open
Shortest
Path First (OSPF)


Routing Decision Criteria



Routers pick different network routes depending on various criteria.



Some routes may be deemed faster by different routing protocols.



Routers keep separate routing tables for each protocol.



A route that is best
now may not be best in a few minutes, depending
on various criteria like traffic, available bandwidth, and link state.



Routing tables keep track of networks, paths to networks, and metrics
associated with each route.



Routers consider two aspects when deci
ding which network routes are
best at a given moment:

o

Administrative Distance

How reliable is the information source
that provided the data about the network route?

o

Routing Protocol Metrics

What are the costs associated with
each network route?


Admini
strative Distance (AD)



Routers learn about networks using various methods:

o

Directly connected

AD = 0. Router learns about the network
firsthand, because it connects to it.

o

Static route

AD = 1. The router does not “see” the network,
but it’s been inform
ed about its existence by a fairly reliable
source (the static route).

o

Connected indirectly

The router heard about it from another
router (EIGRP, SOPF, RIP).



Routers prefer sources with lower AD numbers.



If the same routing protocol finds two different r
outes to the same
destination and the AD is the same, other metrics are considered to
decide which route to use.


Routing Protocol Metrics (Dummies, p. 600)



Each routing protocol calculates the efficiency (the cost) of a route
differently.



Whenever routing
protocols contradict each other, the one with the
lowest AD is preferred.



If the same routing protocol finds two (or more) routes to the same
destination, specific decision criteria are used:

o

Hop count

the number of routers that need to be transversed
(
prefer few hops because there is delay at every hop). RIP uses
hop count metric to choose network routes.

o

Bandwidth

prefer routes with larger bandwidth; very likely
packets will arrive faster. EIGRP uses bandwidth metric to
choose network routes.

o

Delay

Total delay calculated on processing delay, queuing
delay, transmission delay and propagation delay (EIGRP).

o

Reliability

Percentage of time the route is available (EIGRP)

o

Load

Bandwidth consumed by current traffic on a given route
;
the difference betw
een total bandwidth and available bandwidth
of the route (EIGRP).

o

Maximum Transmission Unit (MTU)


The size, in bytes, of each
data packet. The higher the MTU, the more data can be
transferred at once (EIGRP).

o

Cost


Calculated based on the bandwidth of a
network route;
10
8
/bandwidth (OSPF).

Routing Methods (Dummies, p. 602)

Routing protocols use different methods to exchange the info that helps
routers build their routing tables.



Distance vector routing:

o

Build routing tables based on route distance.

o

Excha
nge and combine their rout
ing table with their neighbors
(called convergence).

o

Neighbor routers trust each other’s route information, and they
relay the combined information farther.

o

Routing tables are combined and relayed to all routers in the
network.

o

Be
cause DV routing protocols combine the routing tables of all
routers and propagate them to all neighbors, the convergence
process can be very long in larger networks
.

o

Distance vector routing can cause routing loops so various
features are used to avoid rou
ting loops:



Maximum hop count

never takes route that exceeds
certain number of hops (looping).



Split horizon

prevents route from be advertised back to
its advertiser.



Route poisoning

changes hop count for route that
become unreachable, which disables
a route quickly.



Poison reverse

breaks the split horizon rule ensuring that
all neighbors receive “route down” message as quickly as
possible.



Hold
-
down timer

prevents router from accepting updates
about a router for a certain amount of time if that w
as
reported as down.



Triggered update

allows routers to update each other as
soon as a change occurs, rather than waiting for scheduled
update to be exchanged.

o

Best suited for access or distribution layer routers.

o

RIP and IGRP (replaced by EIGRP) are dis
tance vector routing
protocols.



Link
-
state routing:

o

Build their routing tables independently based on route updates
they receive from their neighbors.

o

Do not merge the routing tables of neighbor routers.

o

Enable routers to have clear image of their neighbor
s, network
topology, and routes to neighbors and beyond.

o

OSPF uses link
-
state routing.



Hybrid routing:

o

Have both distance
vector
and link
-
state
characteristics.

o

Like distance vector protocols …



hybrid routing protocols use distance to evaluate quality of
r
outes.



hybrid routing protocols send route updates that contain
the whole routing table

o

Like link
-
state protocols …



hybrid routing protocols use other metrics in addition to
distance to evaluate the quality of routes.



hybrid routing protocols only exchange
“hello” messages
initially so convergence time is faster than distance vector
protocols.



hybrid routing protocols send updates only when routes
change.

o

Hybrid routing protocols are well
-
suited for core layer,
distribution layer, and even access layer rout
ers.

o

EIGRP is considered a hybrid routing protocol.



RIP
-
2 Basic Concepts (
p. 449)



Routers using RIP
-
2 advertise a small amount of simple information
about each subnet to their neighbors. Their neighbors in turn advertise
the information to their neighbor
s, and so on, until all routers have
learned the information.



RIP routers send periodic routing updates about every 30 seconds by
default. When something changes, the routers will react and converge
to use the then
-
best working routes.



Figure 14
-
3 (p. 449
) shows RIP
-
2 advertising subnet number, mask,
and metric to its neighbors.


Comparing and Contrasting IP Routing Protocols (p. 450)



Important considerations:

o

Is it a public standards (defined in RFCs) or Cisco proprietary?

o

Does the routing protocol suppor
t variable
-
length subnet
masking (VLSM)?


Interior and Exterior Routing Protocols (p. 451)



Two types:

o

Interior Gateway Protocol (IGP)
:
A routing protocol that was
designed and intended for use inside a single autonomous
system
.

o

Exterior Gateway Protocol (E
GP):
A routing protocol that was
designed and intended for use between different autonomous
systems
.



An autonomous system is an internetwork under the administrative
control of a single organization.



Each autonomous system ca
n be assigned a number, called

an
autonomous system number (ASN). Like public IP addresses, the
Internet Corporation for Assigned Network Numbers (ICANN) controls
the worldwide rights to assign ASNs
.



By assigning each autonomous organization an ASN, B
order
G
ateway
P
rotocol (BGP is an E
GP)
can ensure that packets do not loop around
the global Internet by making sure that packets do not pass through
the same autonomous system twice.





Metrics give an objective number to the “goodness” of each route. The
lower the metric, the better the r
oute. Figure 14
-
5 compares two
routes

RIP/hop count and EIRGP/bandwidth.


Autosummarization and Manual Summarization (p. 454)



Routers generally perform routing (forwarding) more quickly with
smaller routing tables, and less quickly with larger routing ta
bles.
Route summarization helps shorten the routing table while retaining all
the needed routes in the network.



Manual summarization gives the network engineer a great deal of
control and flexibility, allowing the engineer to choose what summary
routes to
advertise, instead of just being able to summarize with a
classful network.


Classless and Classful Routing Protocols (p. 454)



Classful routing protocol:

o

m
ust consider the Class A, B, or C network number that a subnet
resides in when performing some of its
tasks.

o

does NOT support VLSM.

o

does NOT send subnet mask in routing updates.

o

does NOT support manual route summarization.



Classless routing protocols d
o not need to consider class rules.

o

DOES support VLSM.

o

DOES send subnet mask in routing updates.

o

DOES sup
port manual route summarization.



The processes used by routing protocols to recognize the changes, to
figure out the now
-
best

routes to each subnet, and to change all the
routers’ routing tables, is called
convergence
. Some routing protocols
converge
more
quickly
than others.



Later
-
defined IGPs typically support some kind of authentication as a
means of mitigating possible DoS attacks.





Configuring and Verifying RIP
-
2 (p. 456)



Three
-
step process:

o

Step 1
-

Use the
router rip
configuration command to move
into
RIP configuration mode.

o

Step 2
-

Use the
version 2
RIP subcommand to tell the router to
use RIP Version

2 exclusively.

o

Step 3
-

Use one or more
network

net
-
number
RIP
subcommands to enable RIP on the correct interfaces.



Each RIP network command enabl
es RIP on a set of interfaces.



The RIP network command only uses a classful network number as its
one parameter.



For any of the router’s interface IP addresses in that entire classful
network, the router

does the following three things:

o

The router multic
asts routing updates to a reserved IP multicast
IP address, 224.0.0.9.

o

The router listens for incoming updates on that same interface.

o

The router advertises about the subnet connected to the
interface.



Sample RIP configuration on page 457.



RIP configuratio
n does not provide a way to enable RIP on only some
interfaces so the network must be configured then use the
passive
-
interface

type
-
number
RIP subcommand to stop sending RIP updates
out that interface.



IOS includes three primary
show
commands to confirm h
o
w well RIP
-
2 is working (detailed example begins on p. 459).




Of particular importance for real
-
life troubleshooting and for the exam, focus
on both the version information and the routing information sources. If you
forget to configure the version 2 c
ommand on one router, that router will
send only RIP
-
1 updates by default, and the column labeled “Send” would
list a 1 instead of a 2. The other routers, only listening for Version 2
updates, could not learn routes from this router.


(Text goes over Admin
istrative Distance, see notes from Dummies book,
above.)


Examining RIP Messages with debug (p. 464)



The best way to understand whether RIP is doing its job is to use the
debug ip rip
command. This command enables a debug option that
tells the router to ge
nerate log messages each time the router sends
and receives a RIP update.



Example 14
-
9 shows the output generated by the
debug ip rip

command on the Albuquerque router, based on Figure 14
-
1. Note that
to see these messages, the user needs to be connected t
o the console
of the router, or use the terminal monitor privileged mode

EXEC
command if using Telnet or SSH to connect to the router.



A close examination of the number of subnets in each routing update
(Example 14
-
9)
shows that the routers do not advertis
e all routes in
the updates. The reason has to do with the theory behind RIP,
specifically a feature called split horizo
n. This loop
-
avoidance feature
limits which subnets are advertised in each update to help avoid some
forwarding loops.



Before using the
debug
command, look at the router’s CPU utilization
with the show process command. On routers with a higher CPU
utilization, generally above 30 to 40 percent, be very cautious when
enabling debug options, as this may drive the CPU to the point of
impacting
packet forwarding.



To make the router generate time stamps, you need to configure the
service timestamps global configuration command.






“Do I Know This Already” Quiz,
Chapter 14

-
pp.
436
-
438


TOPIC

Q#

1
st
Try

2
nd
Try

Answer

1

B
, C


A, C

Connected and Static
Routes

2

A,
C, D


A

3

A


A,
B

4

E, F



5

B


B
, D, E,
F

Routing Protocol Overview

6

B
, D, E


D, E,
F

7

A, D,
G
,
I


A, D,
E
,
H

8

F


A

9

D, E, F


B

Configuring and Verifying
RIP
-
2

10

B, C,
F


B, C


Q
1
:

Which of the following must
be true for a static route to be installed in a

router’s IP routing table?

a. The outgoing interface associated with the route must be in an “up
and up” state.

b. The router must receive a routing update from a neighboring router.

c. The ip route command
must be added to the configuration.

d. The outgoing interface’s ip address command must use the special
keyword.


Answer:
A, C

Explanation:

Typo

I really meant A. B is not correct since configuring static
routes do not rely on learning routes from neigh
bors (that would be dynamic
routing).


Q2
:

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 ser
ial 0


Answer:
A

Explanation:
Commands for static route include destination IP, subnet mask,
and next
-
hop
-
ip | interface. B is not correct because there is no subnet
mask. C and D are not correct because it must be dotted decimal format.


Q3
:

Which of the
following routing protocols are considered to use distance
vector logic?

a. RIP

b. IGRP

c. EIGRP

d. OSPF


Answer:
A and B

Explanation:
I forgot about IGRP. The Dummies books says that isn’t used
anymore

it was replaced by EIGRP.


Q5
:

Which of the followi
ng routing protocols support VLSM?

a. RIP

b. RIP
-
2

c. IGRP

d. EIGRP

e. OSPF

f. Integrated IS
-
IS


Answer:
B, D, E and F

Explanation:
A is not correct

RIP does not send subnet mask so variable
-
length subnet mask would not be supported. C is not correct

I
GRP is also
old, not supported. Basically, new ones
support VLSM old ones don’t.


Q6
:

Which of the following routing protocols are considered to be capable of


converging

quickly?

a. RIP

b. RIP
-
2

c. IGRP

d. EIGRP

e. OSPF

f. Integrated IS
-
IS


Answer:

D, E and F

Explanation:
I said B, D and F. B is not correct

both RIP and RIP
-
2 send
the whole routing table so convergence won’t be quick. Hybrid and link
-
state
don’t merge tables, so convergence is faster

that would be EIGRP, OSPF
and Integrated IS
-
I
S.


Q7
:

Router1 has interfaces with addresses 9.1.1.1 and 10.1.1.1. Router2,


connected to Router1 over a serial link, has interfaces with addresses


10.1.1.2 and 11.1.1.2. Which of the following commands would be part


of a complete R
IP Version 2 configuration on Router2, with which


Router2 advertises out all interfaces, and about all routes?

a.
router rip

b.
router rip 3

c.
network 9.0.0.0

d.
version 2

e.
network 10.0.0.0

f.
network 10.1.1.1

g.
network 10.1.1.2

h.
network 11.0
.0.0

i.
network 11.1.1.2


Answer:
A, D, E, H

Explanation:
I said A, D, G, I. A is correct because we are configuring with
RIP routing protocol. D is correct because we are using RIP
-
2, not RIP. Other
answers were wrong because I misread the question

I th
ought we were
configuring Router 1, so network numbers for that router (answers G and I)
would not be used. We are configuring Router 2, so static routes to Router 1
addresses would be configured. **Is H a mistake? 11.0.0.0 is on Router 2.


Q8
:

Which of th
e following network commands, following a router rip


command, would cause RIP to send updates out two interfaces whose


IP addresses are 10.1.2.1 and 10.1.1.1, mask 255.255.255.0?

a. network 10.0.0.0

b. network 10.1.1.0 10.1.2.0

c. network 1
0.1.1.1. 10.1.2.1

d. network 10.1.0.0 255.255.0.0

e. network 10

f. You cannot do this with only one network command.


Answer:
A

Explanation:
I said F because I thought you had to do the thing where you
configure RIP for the whole router then disable some o
f the interfaces. A is
correct because that is the address
for the network that the two interfaces
are part of. B and C are not correct because you can’t put two IP addresses
in the same command plus using the IP address for the entire network
covers both
bases with one command. Answer E is not correct

“10” is not a
valid address.


Q9
:

What command(s) list(s) information identifying the neighboring routers


that are sending routing information to a particular router?

a. show ip

b. show ip protocol

c. show ip routing
-
protocols

d. show ip route

e. show ip route neighbor

f. show ip route received


Answer:
B

Explanation:
I said D, E and F. Per Table 14
-
5, show ip protocol “l
ists
information about the RIP configuration, plus the IP addresses of
neighbori
ng RIP routers from which the local router has learned routes.
” D,
E, and F are not correct


show ip route
command shows learned routes
but not IP addresses from which those routes were learned. I haven’t found
any documentation that shows that E or F use
correct syntax.


Q10
:

Review the snippet from a show ip route command on a router:


R 10.1.2.0 [120/1] via 10.1.128.252, 00:00:13, Serial0/0/1


Which of the following statements are true regarding this output?

a. The administrative distance
is 1.

b. The administrative distance is 120.

c. The metric is 1.

d. The metric is not listed.

e. The router added this route to the routing table 13 seconds ago.

f. The router must wait 13 seconds before advertising this route again.


Answer:
B and C

Expla
nation:
I said B, C and F.
F is not correct
-
the time listed is the
amount of
time since the router last heard about this route.