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Cisco Systems CCNA Version 3 Semester 1
Module 10
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 1
Overview
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 2
Module 10: Routing Fundamentals and Subnets
10.1 Routed Protocol
10.1.1 Routable and routed protocols
10.1.2 IP as a routed protocol
10.1.3 Packet propagation and switching within a router
10.1.4 Internet Protocol (IP)
10.1.5 Anatomy of an IP packet
10.2 IP Routing Protocols
10.2.1 Routing overview
10.2.2 Routing versus switching
10.2.3 Routed versus routing
10.2.4 Path determination
10.2.5 Routing tables
10.2.6 Routing algorithms and metrics
10.2.7 IGP and EGP
10.2.8 Link state and distance vector
10.2.9 Routing protocols
10.3 The Mechanics of Subnetting
10.3.1 Classes of network IP addresses
10.3.2 Introduction to and reason for subnetting
10.3.3 Establishing the subnet mask address
10.3.4 Applying the subnet mask
10.3.5 Subnetting Class A and B networks
10.3.6 Calculating the resident subnetwork through ANDing
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 3
10.1.1 Routable and routed protocols
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 4
10.1.1 Routable and routed protocols
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The network address is obtained by ANDing the address with the network mask.
The reason that a network mask is used is to allow groups of sequential IP
addresses to be treated as a single unit.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 5
IP is a connectionless, unreliable,
best-effort delivery protocol.
IP determines the
most efficient route
for data, based on
the routing protocol.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 6
10.1.2 IP as a routed protocol
MACd MACs
IPs
IPd
Ps Pd
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 7
10.1.3 Packet propagation and switching within a router
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Reliable
connection-oriented
Ps Pd
IPs
IPd
MACd MACs
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 8
IP
Header
MAC
destination
Frame Trailer
(FCS/CRC)
IP
source
MAC
source
IP
destination
Frame
Header
Port
destination
Segment
Header
MACd MACs
IPs
IPd
Port
source
Ps Pd
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 9
One Complete Maximum Frame
IP addresses
Data…
…Data…
IP Header
FCS
…Data…
MAC addresses
Frame Header
MACd MACs
…Data
IPs
IPd
Ps Pd
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 10
10.1.3 Packet propagation and switching within a router
Each time a packet is switched from one router interface to another
the packet is de-encapsulated then encapsulated once again.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 11
10.1.3 Packet propagation and switching within a router
IPs
IPd
Ps Pd
MACd MACs
The Empty Frame is
Thrown Away…
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The MAC address is changed each time the packet passes
through a router.
The Router interface is part of the attached LAN. Like a host,
the router uses the MAC address to exchange topological
(physical) information.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 12
10.1.3 Packet propagation and switching within a router
Eventually these discarded Mac addresses
will pile up and should be returned to the
Manufacturer for recycling.
Discarded MAC
addresses
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 13
10.1.3 Packet propagation and switching within a router
MACd MACs
IPs
IPd
…and a new one is created with the Router’s Mac address.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 14
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 15
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 16
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 17
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 18
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 19
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 20
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 21
10.1.3 Packet propagation and switching within a router
Routers determine the subnet network address based upon a given IP address and
subnet mask by binary ANDing the two together.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 22
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 23
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 24
10.1.3 Packet propagation and switching within a router
Ps Pd
IPs
IPd
MACd MACs
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 25
10.1.3 Packet propagation and switching within a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 26
10.1.4 Internet Protocol (IP)
IP is a connectionless service. The route that
the packet takes is determined by the routers.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 27
WAN Services
Dedicated Physical - PPP
ISDN – Private Physical Switched
private
Frame Relay - Private Packet Switched
VPN - Public Packet Switched
internet
Point of
Demarcation
Many ways
to do this.
The Telephone
Company owns all
the infrastructure
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 28
10.1.5 Anatomy of an IP packet
IP Stuff
MACd MACs
IPs
IPd
Ps Pd
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 29
IP Stuff
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Version – Indicates the version of IP currently used; four bits. If the version field is different than
the IP version of the receiving device, that device will reject the packets.
*IP header length (HLEN) – Indicates the datagram header length in 32-bit words. This is the total
length of all header information, accounting for the two variable-length header fields.
Type-of-service (TOS) – Specifies the level of importance that has been assigned by a particular
upper-layer protocol, eight bits.
Total length – Specifies the length of the entire packet in bytes, including data and header, 16 bits.
To get the length of the data payload subtract the HLEN from the total length.
Identification – Contains an integer that identifies the current datagram, 16 bits. This is the
sequence number.
*Flags – A three-bit field in which the two low-order bits control fragmentation. One bit specifies
whether the packet can be fragmented, and the other specifies whether the packet is the last
fragment in a series of fragmented packets.
Fragment offset – Used to help piece together datagram fragments, 13 bits. This field allows the
previous field to end on a 16-bit boundary.
*Time-to-live (TTL) – A field that specifies the number of hops a packet may travel. This number is
decreased by one as the packet travels through a router. When the counter reaches zero the packet
is discarded. This prevents packets from looping endlessly.
Protocol – indicates which upper-layer protocol, such as TCP or UDP, receives incoming packets after
IP processing has been completed, eight bits.
Header checksum – helps ensure IP header integrity, 16 bits.
IP Source
IP Destination
Options – allows IP to support various options, such as security, variable length.
*Padding – extra zeros are added to this field to ensure that the IP header is always a multiple of
32 bits.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 30
Module 10: Routing Fundamentals and Subnets
10.1 Routed Protocol
10.1.1 Routable and routed protocols
10.1.2 IP as a routed protocol
10.1.3 Packet propagation and switching within a router
10.1.4 Internet Protocol (IP)
10.1.5 Anatomy of an IP packet
10.2 IP Routing Protocols
10.2.1 Routing overview
10.2.2 Routing versus switching
10.2.3 Routed versus routing
10.2.4 Path determination
10.2.5 Routing tables
10.2.6 Routing algorithms and metrics
10.2.7 IGP and EGP
10.2.8 Link state and distance vector
10.2.9 Routing protocols
10.3 The Mechanics of Subnetting
10.3.1 Classes of network IP addresses
10.3.2 Introduction to and reason for subnetting
10.3.3 Establishing the subnet mask address
10.3.4 Applying the subnet mask
10.3.5 Subnetting Class A and B networks
10.3.6 Calculating the resident subnetwork through ANDing
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 31
10.2.1 Routing overview
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 32
10.2.1 Routing overview
The router compares available routing
table information to select the best path.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 33
10.2.1 Routing overview
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Routing metrics are values used in determining the advantage of one route over another.
Routing protocols use various combinations of metrics for determining the best path for data.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 34
10.2.1 Routing overview
MACd MACs
IPs
IPd
Ps Pd
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 35
10.2.2 Routing versus Switching
Routing is a hierarchical organizational scheme that allows individual addresses to be
grouped together; the same as area codes in the telephone network.
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016139337917
Routers must maintain routing tables and
make sure other routers know of changes in
the network topology.
This function is performed using a routing
protocol.
The router must use the routing table to
determine where to send packets.
The router switches the packets to the
appropriate interface, adds the necessary
framing information for the interface, and
then transmits the frame.
IP address ? Telephone number ? Social Security Number ?
You need a subnet mask to know.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 36
Routable Protocols
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This course focuses on Internet Protocol (IP).
Other routable or routed protocols include DecNet,
IPX/SPX, XNS and AppleTalk.
These protocols provide Layer 3 support.
Non-routable protocols do not provide Layer 3
support.
The most common non-routable protocol is NetBEUI.
NetBEUI is a small, fast, and efficient protocol that
is limited to frame delivery within one segment.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 37
3
10.2.2 Routing versus Switching
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 38
10.2.2 Routing versus Switching
On the WAN side, the router
keeps a Routing Table.
E1 is just another NIC on the
network. The router keeps
the same arp table as any of
the hosts on that network.
S1
S1
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 39
10.2.2 Routing versus Switching
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 40
RoutED
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Includes any network protocol that provides enough information in its network layer
address for a router to forward it to the next device and thence to its destination.
Defines the format and use of the fields within a packet.
The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX) are
examples of routed protocols. Other examples include DECnet, AppleTalk, Banyan
VINES, and Xerox Network Systems (XNS).
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 41
10.2.3 Routed versus routing
RoutING
Link State
Distance Vector
1.
2.
3.
4.
5.
Routing Information Protocol (RIP)
Interior Gateway Routing Protocol (IGRP)
Open Shortest Path First (OSPF)
Border Gateway Protocol (BGP)
Enhanced IGRP (EIGRP).
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 42
Distance Vector
IGP
EGP
IGP
Link State
IGP
IGP
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 43
10.2.4 Path determination
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Routes configured manually by the network administrator are static routes.
Routes learned by others routers using a routing protocol are dynamic routes.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 44
10.2.4 Path determination
Each intersection
is a router
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 45
10.2.4 Path determination
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 46
10.2.5 Routing tables
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Routing Information Protocol (RIP) uses hop count as its only routing metric.
Interior Gateway Routing Protocol (IGRP) uses a combination of bandwidth, delay,
load, and reliability metrics to create a composite metric value.
S0
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 47
10.2.6 Routing algorithms and metrics
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Bandwidth
Delay
Load
Reliability
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 48
10.2.6 Routing algorithms and metrics
1.
2.
3.
4.
5.
6.
7.
Bandwidth – The data capacity of a link. Normally, a 10-Mbps Ethernet link is
preferable to a 64-kbps leased line.
Delay – The length of time required to move a packet along each link from source to
destination. Delay depends on the bandwidth of intermediate links, the amount of
data that can be temporarily stored at each router, network congestion, and physical
distance.
Load – The amount of activity on a network resource such as a router or a link.
Reliability – Usually a reference to the error rate of each network link.
Hop count – The number of routers that a packet must travel through before
reaching its destination. Each router the data must pass through is equal to one hop.
A path that has a hop count of four indicates that data traveling along that path
would have to pass through four routers before reaching its final destination. If
multiple paths are available to a destination, the path with the least number of hops
is preferred.
Ticks – The delay on a data link using IBM PC clock ticks. One tick is approximately
1/18 second.
Cost – An arbitrary value, usually based on bandwidth, monetary expense, or other
measurement, that is assigned by a network administrator.
Bad Dogs Love Routing Hairy Tom Cats
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 49
10.2.6 Routing algorithms and metrics
1.
2.
3.
4.
5.
Optimization – Optimization describes the capability of the routing algorithm
to select the best route. The route will depend on the metrics and metric
weightings used in the calculation. For example, one algorithm may use both hop
count and delay metrics, but may consider delay metrics as more important in
the calculation.
Simplicity and low overhead – The simpler the algorithm, the more efficiently
it will be processed by the CPU and memory in the router. This is important so
that the network can scale to large proportions, such as the Internet.
Robustness and stability – A routing algorithm should perform correctly when
confronted by unusual or unforeseen circumstances, such as hardware failures,
high load conditions, and implementation errors.
Flexibility – A routing algorithm should quickly adapt to a variety of network
changes. These changes include router availability, router memory, changes in
bandwidth, and network delay.
Rapid convergence – Convergence is the process of agreement by all routers on
available routes. When a network event causes changes in router availability,
updates are needed to reestablish network connectivity. Routing algorithms that
converge slowly can cause data to be undeliverable.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 50
10.2.7 IGP and EGP
(RIP) and (RIPv2) (IGRP) (EIGRP) (OSPF) (IS-IS)
Interior Gateway
Protocols
Exterior Gateway
Protocols
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 51
10.2.8 Link state and distance vector
IGPs can be further categorized as either:
1.
Distance-Vector protocols - RIP IGRP EIGRP
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Routing by rumor
2. Link-State protocols.
Link-state advertisements are caused by…
topology changes
link-state refresh packets
1.
2.
Distance-Vector protocols “Psst! Hey neighbor,
remember who I know about?”
Link-State protocols. “Listen up everybody, there’s
a change to the networks that I’m connected to.”
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 52
Module 10: Routing Fundamentals and Subnets
10.1 Routed Protocol
10.1.1 Routable and routed protocols
10.1.2 IP as a routed protocol
10.1.3 Packet propagation and switching within a router
10.1.4 Internet Protocol (IP)
10.1.5 Anatomy of an IP packet
10.2 IP Routing Protocols
10.2.1 Routing overview
10.2.2 Routing versus switching
10.2.3 Routed versus routing
10.2.4 Path determination
10.2.5 Routing tables
10.2.6 Routing algorithms and metrics
10.2.7 IGP and EGP
10.2.8 Link state and distance vector
10.2.9 Routing protocols
10.3 The Mechanics of Subnetting
10.3.1 Classes of network IP addresses
10.3.2 Introduction to and reason for subnetting
10.3.3 Establishing the subnet mask address
10.3.4 Applying the subnet mask
10.3.5 Subnetting Class A and B networks
10.3.6 Calculating the resident subnetwork through ANDing
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 53
10.3.1 Classes of network IP addresses
EG: An IP address 172.32.65.13 and a default subnet mask,
the host belongs to the 172.32.0.0 network.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 54
10.3.2 Introduction to and reason for subnetting
The benefits of Subnetting
1.
smaller broadcast domains
2.
low-level security provided
3.
increased address flexibility
EG: In a class C network a subnet mask of 255.255.255.224 will create 6
useable subnets each with 32 useable hosts.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 55
10.3.2 Introduction to and reason for subnetting
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Host bits of the network address are all equal to 0.
Host bits of the broadcast address are all equal to 1.
Host bits are reassigned as network bits.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 56
10.3.2 Introduction to and reason for subnetting
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 57
10.3.3 Establishing the subnet mask address
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 58
10.3.3 Establishing the subnet mask address
Assume Class C subnetting
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 59
10.3.3 Establishing the subnet mask address
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 60
10.3.3 Establishing the subnet mask address
Magic Numbers
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 61
10.3.4 Applying the subnet mask
Assumes subnet mask of
255.255.255.224 resulting
in a magic number = 32
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 62
10.3.4 Applying the subnet mask
Magic Numbers
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 63
10.3.5 Subnetting Class A and B networks
16 bits are available for Class B host IP
addresses using the default subnet mask.
Applying the subnet mask 255.255.255.240 (/28) to a
Class B network will give 4094 useable subnets and 14
useable hosts/subnet.
If you applied the subnet mask 255.255.255.0 to
a Class B network it would give you 254 useable
subnets and 254 useable hosts/subnet.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 64
10.3.5 Subnetting Class A and B networks
To borrow 20 bits you would use subnet mask
255.255.255.240 = /28
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 65
10.3.5 Subnetting Class A and B networks
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 66
10.3.5 Subnetting Class A and B networks
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 67
10.3.5 Subnetting Class A and B networks
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 68
10.3.6 Calculating the resident subnetwork through ANDing
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 69
10.3.6 Calculating the resident subnetwork through ANDing
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 70
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 71
FIN
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod10 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 72