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CCNA Semester 3
Chapter 01Chap
ter 01
CLASSLESSCLASSLESSROUTINGROUTING
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ObjectivesObjectives
Define VLSM and briefly describe the reasons for itsuse
Divide a major network into subnets of different sizesusing VLSM
Define route aggregation and summarization as theyrelate to VLSM
Configure a router using VLSM
Identify the key features of RIP v1 and RIP v2
Identify the important differences between RIP v1and RIP v2
Configure RIP v2
Verify and troubleshoot RIP v2 operation
Configure default routes using the ip route and ipdefault-network commands
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Table of ContentTable of Content
1VLSM
2 CIDR
3 Classless routing
4RIP version 2
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VLSMVLSM
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Issues with IP AddressingIssues with IP Addressing
IP addressing crisis
As early as 1992, the IETF identified twospecific concerns:
IP address exhaustion
Routing table growth
U N I V E R S I T YU N I V E R S I T Y
Internet
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IP Addressing SolutionsIP Addressing Solutions
Short term to extension to IPv4 Subneting masking: RFCs 950, 1812
Variable-length subnet masks: RFC 1812
Classless interdomain routing: RFCs 1518,1519, 2050
Address allocation for private Internets:RFC 1918
Network AddressTranslation: RFC 1631
Route summarization: RFC 1518
Ultimate solution: IPv6 128-bit address
space
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172.16.14.32/27
172.16.14. 64/27
172.16.14.96/27
What is VLSM ?What is VLSM ?
Subnet 172.16.14.0/24 is divided into smallersubnets (Sub-subnet):
Subnet with one mask at first (/27)
Further subnet one of these subnets notused elsewhere (/30)
CC
BB
AA
HQHQ
172.16.1.0/24
172.16.2.0/24
HQHQ172.16.0.0/16
172.16.14.136/30
172.16.14.132/30
172.16.14.140/30
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A waste of spaceA waste of space
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When to use VLSM?When to use VLSM?
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Calculating subnets with VLSMCalculating subnets with VLSM
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Calculating subnets with VLSM (2)Calculating subnets with VLSM (2)
Derived from the
172.16.32.0/20Subnet 172.16.33.0/3
0
172.16.32.0/26
172.16.32.64/26
172.16.32.128/2
6
172.16.32.192/26
26-Bit Mask (62 Hosts)
Derived from the
172.16.33.0/26 Subnet
30-Bit Mask (2 Hosts)
172.16.33.12/30
172.16.33.8/30
172.16.33.4/30
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Exercise Calculating subnets with VLSMExercise Calculating subnets with VLSM
60 Hosts 12 Hosts 12 Hosts
Using VLSMs, define appropriate subnets for addressing thenetworks using 192.168.10.0/24.
28 HostsKL
SydneyPerth Singapore
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Exercise Calculating subnets with VLSMExercise Calculating subnets with VLSM
60 Hosts 12 Hosts 12 Hosts
192.168.10.0/24
KL
SydneyPerth Singapore
192.168.10.64/27
192.168.10.128/30192.168.10.132/30 192.168.10.136/30
28 Hosts
192.168.10.0/26 192.168.10.96/28 192.168.10.112/2
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Classless Interdomain RoutingClassless Interdomain Routing
CIDR is a mechanism developed to alleviateexhaustion of addresses and reduce routing tablesize.
Block addresses can be summarized into singleentries without regard to the classful boundary ofthe network number.
Summarized blocks are installed in routing tables.
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Route aggregation with VLSMRoute aggregation with VLSM
KLSydney
Perth
Singapore
192.168.48.0/24192.168.49.0/24192.168.50.0/24192.168.51.0/2
4
192.168.52.0/2
4192.168.53.0/24192.168.54.0/24192.168.55.0/24192.168.56.0/2
4192.168.57.0/24192.168.63.0/24
19
2.168.
56.0/21
192.168.52.0/22
192.168.48.0/20
192.168.48.0/22
Upstream
provider
Upstream
provider
Route summarization reduces routing table sizeby aggregating routes to multiple networks intoone supernet
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Route summarization exampleRoute summarization example
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Configuring VLSMConfiguring VLSM
60 Hosts 12 Hosts 12 Hosts
192.168.10.0/24
KL
SydneyPerth Singapore
192.168.10.64/27
192.168.10.128/30192.168.10.132/30
192.168.10.136/30
28 Hosts
192.168.10.0/26 192.168.10.96/28 192.168.10.112/2
S010.137
S0 10.138
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CLASSLESS ROUTING
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Network Summarization in Classful Routing
Summary routes are exchanged betweenforeign networks
Summary routes are automatically created atClass A, B, and C network boundaries
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Classful Subnet Issues
All router interfaces within the same networkmust have the same subnet mask.
This approach may not fully use availableallocation of host addresses.
All subnets of the same major network must
be contiguous.
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IP Routing TableIP Routing Table with a Classful Protocolwith a Classful Protocol
p1r3# show ip route
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
10.0.0.0/24 is subnetted, 3 subnets,
R 10.1.1.0/24 [120/1] via 10.1.2.2, 00:00:05, Ethernet0
C 10.1.2.0/24 is directly connected, Ethernet0
R 10.1.3.0/24 [120/2] via 10.1.2.2, 00:00:05, Ethernet0R 192.168.24.0/24 [120/2] via 10.1.2.2, 00:00:16, Ethernet0
R 172.16.0.0/16 [120/3] via 10.1.2.2, 00:00:16, Ethernet0
R* 0.0.0.0/0 [120/3] via 10.1.2.2, 00:00:05, Ethernet0
Where will the router send traffic bound for the
following destinations?
192.168.24.3
172.16.5.1
10.1.2.7
200.100.50.0
10.2.2.2
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The IP Classless CommandThe IP Classless Command
Router(config)# ip classlessRouter(config)# ip classless
Replaces the default behavior of classful routingprotocols to match against only known subnets of
a major network Changes default behavior of classful routingprotocol for unknown subnets
On by default in Cisco IOS version 12.0 and later
Has no effect on most classless routing protocolsbecause they use the longest-match criteriaby default
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WithoutWithout ip classlessip classless commandcommand
BHMGAD
S0/0
192.168.13.2
To10.2.2.4
192.168.1.4/30
10.1.1.0
10.3.3.0
Fa0/1
Fa0/0
Destination network Outbound interface
10.3.3.0 Fa0/1
10.1.1.0 Fa0/0
0.0.0.0 S0/0
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WithWith ip classlessip classless commandcommand
BHMGAD
S0/0
192.168.13.2
To10.2.2.4
192.168.1.4/30
10.1.1.0
10.3.3.0
Fa0/1
Fa0/0
Destination network Outbound interface
10.3.3.0 Fa0/1
10.1.1.0 Fa0/0
0.0.0.0 S0/0
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Classless Routing OverviewClassless Routing Overview
Classless routing protocols include the subnet mask withthe route advertisement.
Classless routing protocols support VLSM.
Summary routes can be manually controlled within thenetwork.
Example of classless routing protocols are as follows: OSPF
EIGRP
RIPv2 IS-IS
BGPv4
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Classless Subnetting Requirements
Router interfaces within the same networkcan have different subnet masks:
VLSM is supported
This approach maximizes allocation ofavailable host addresses.
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Automatic Network-Boundary Summarization
EIGRP on both Router A and Router B
advertises a summarized route to172.16.0.0/16.
Router C receives two routes to 172.16.0.0/16.
Router A or B, or both, should be configured
to not summarize.
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Effect of the auto-summary Command
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Effect of the no auto-summary Command
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RIP Version 2RIP Version 2
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RIP v1:RIP v1: CharacteristicsCharacteristics
IGP protocol, is classful routing. It is a distance vector protocol that uses a
hop count metric.
The maximum number of hops is 15. By default, routing updates are broadcast
every 30 seconds.
The router applies the one subnet mask thatis configured on the receiving interface toreceive network information.
Load balancing over as many as six equal-
cost paths, with four paths as the default.
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RIP v1:RIP v1: LimitationsLimitations
It does not send subnet mask information inits updates.
It sends updates as broadcasts on255.255.255.255.
It does not support authentication.
It is not able to support VLSM or classlessinterdomain routing (CIDR).
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RIP v1:RIP v1: ConfigurationConfiguration
NOTE:
Subnets will be understood as major network
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RIP v2 featuresRIP v2 features
Send out subnet mask information with theroute update.
Support VLSM or classless interdomain routing
(CIDR). Provides for authentication in its updates.
Provides Multicast routing updates, using the
Class D address 224.0.0.9. Use external route tags
Routing update is includes a next-hop routeip address.
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Comparing RIP v1 and v2Comparing RIP v1 and v2
RIP v1
Easy to configure.
Only supports classfulrouting protocol
No subnet informationwith routing update.
Does not support prefixrouting all the devices
in the same networkmust use same subnetmask.
No authentication in
updates
RIP v2
Easy to configure.
Supports use classless routing
Send subnet information withrouting updates.
Support prefix routing different subnets within thesame network can have
different subnet masks. Provides for authentication in
its updates.
Provides multicast routingupdates
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RIP v2:RIP v2: ConfigurationConfiguration
router rip
version 2
network 150.100.0.0
router rip
version 2
network 150.100.0.0
Kuala Lumpur Bangkok
150.100.4.0/24
150.100.2.0/24
150.100.3.0/24
NOTE:
Assigning IP network numbers without specifyingsubnet values
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Discontiguous subnets and classless routingDiscontiguous subnets and classless routing
RIP v1 always uses automatic summarization.
The default behavior of RIP v2 is to summarize at
network boundaries the same as RIP v1.
router ripversion 2no auto-summary
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Verifying RIP v2 :Verifying RIP v2 : SHOW IP PROTOCOLSSHOW IP PROTOCOLS
BA
172.16.1.1
192.168.1.0172.16.1.0
10.1.1.1 10.1.1.2
10.2.2.2
10.2.2.3
192.168.1.1
B
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Verifying RIP v2:Verifying RIP v2: SHOW IP ROUTESHOW IP ROUTE
BA
172.16.1.1
192.168.1.0172.16.1.0
10.1.1.1 10.1.1.2
10.2.2.2
10.2.2.3
192.168.1.1
B
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Troubleshooting RIP v2 :Troubleshooting RIP v2 : DEBUG IP RIPDEBUG IP RIP
BA
172.16.1.1
192.168.1.0172.16.1.0
10.1.1.1 10.1.1.2
10.2.2.2
10.2.2.3
192.168.1.1
B
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Other RIPv2 Commands (EXTRA)Other RIPv2 Commands (EXTRA)
Router(config-router)# neighbor ip-addressDefines a neighboring router with which to exchange
unicast routing information. (RIPv1 or RIPv2)
Router(config-if)# ip rip send|receive version 1 | 2 | 1
2
Configures an interface to send/receive RIP Version 1 and/orVersion 2 packets
Router(config-if)# ip summary-address rip ip_address
ip_network_mask
Specifies the IP address and network mask that identify theroutes to be summarized.
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