CCNA Routing Protocols and Concepts, Chapter 6: VLSM and CIDR
255.255.255.192
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252
The shortage of ip addresses
The difficulty of assigning static IP addresses to hosts in large enterprises
The complexity of implementing advanced routing protocols such as OSPF and EIGRP.
The shortage of network administrators qualified in the use of RIP v1 and EIGRP.
255.255.255.252 for QA
255.255.255.224 for Sales
255.255.255.240 for QA
255.255.255.248 for QA
255.255.255.0 for Sales
The network for a default route
A network that contains both private and public addresses
A set of discontiguous networks that are controlled by an ISP
A summarization of several IP classful networks into one IP address range
OSPF
RIPv1
RIPv2
EIGRP
BGP
/31
/30
/29
/28
/27
VLSM
CIDR
Private IP Addresses
Classful Routing
192.168.4.3/29
192.168.4.15/29
192.168.4.65/26
192.168.4.255/24
6
14
29
34
62
Because RIPv2 does not support VLSM, the subnet masks will not be allowed.
The subnets will not have enough host addresses for the given network requirements.
The subnets overlap and will be rejected by the router.
The router will support the addressing scheme.
None
8
16
24
26
Host B has a defective Ethernet card.
The default gateway on Host B is not correctly set.
There is a layer 2 problem between R2 and Host B
R2 does not have routes back to networks connected to R1.
32-bit address
Next hop router interface
Subnet mask
Unicast host address
Layer 2 address
192.168.0.0 - 192.168.32.0/24
192.168.0.0 - 192.168.47.0/24
192.168.32.0 - 192.168.47.0/24
192.168.32.0 - 192.168.48.0/24
192.168.32.0 - 192.168.63.0/24
3
4
12
36
84
Reduced routing table size.
Dynamic address assignment.
Automatic route distribution.
Reduced routing update traffic.
Automatic summarization at classful boundaries.
192.168.1.16/26
192.168.1.96/28
192.168.1.160/28
192.168.1.196/27
192.168.1.224/28
192.168.1.5/30
192.168.2.17/28
192.168.2.63/27
192.168.2.130/25
192.168.0.0/23
192.168.0.0/22
192.168.0.0/21
192.168.0.0/20
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