qspiders - variable length-subnet-masks
TRANSCRIPT
Variable-Variable-Length Length Subnet Subnet MasksMasks
© 2001, Cisco Systems, Inc. 3-13-1
What Is a Variable-Length Subnet Mask?
HQ 172.16.0.0/16
HQ
172.16.1.0/24
172.16.2.0/24
HQ 172.16.0.0/16
What Is a Variable-Length Subnet Mask? (cont.)
172.16.14.32/27
172.16.14. 64/27
172.16.14.96/27C
B
A
–Subnet 172.16.14.0/24 is divided into smaller subnets:• Subnet with one mask at first (/27)
HQ
172.16.1.0/24
172.16.2.0/24
HQ 172.16.0.0/16
What Is a Variable-Length Subnet Mask? (cont.)
172.16.14.32/27
172.16.14. 64/27
172.16.14.96/27
• Subnet 172.16.14.0/24 is divided into smaller subnets:• Subnet with one mask at first (/27)• Then further subnet one of the unused /27 subnets into
multiple /30 subnets
C
B
A
HQ
172.16.1.0/24
172.16.2.0/24
HQ 172.16.0.0/16172.16.14.136/30
172.16.14.132/30
172.16.14.140/30
What Is a Variable-Length Subnet Mask? (cont.)
Calculating VLSMs
Subnetted Address: 172.16.32.0/20In Binary 10101100. 00010000.00100000.00000000
Calculating VLSMs (cont.)
VLSM Address: 172.16.32.0/26In Binary 10101100. 00010000.00100000.00000000
Subnetted Address: 172.16.32.0/20In Binary 10101100. 00010000.00100000.00000000
Network Subnet VLSM subnet
Host
10101100 . 00010000 .0010 0000.00 000000=172.16.32.0/261st subnet:
VLSM Address: 172.16.32.0/26In Binary 10101100. 00010000.00100000.00000000
Subnetted Address: 172.16.32.0/20In Binary 10101100. 00010000.00100000.00000000
Calculating VLSMs (cont.)
Subnetted Address: 172.16.32.0/20In Binary 10101100. 00010000.00100000.00000000
VLSM Address: 172.16.32.0/26In Binary 10101100. 00010000.00100000.00000000
1st subnet: 10101100 . 00010000 .0010 0000.00 000000=172.16.32.0/26172 . 16 .0010 0000.01 000000=172.16.32.64/26172 . 16 .0010 0000.10 000000=172.16.32.128/26172 . 16 .0010 0000. 1 000000=172.16.32.192/26172 . 16 .0010 0001.00 000000=172.16.33.0/26
Network Subnet VLSM Subnet
Host
1
2nd subnet:3rd subnet:4th subnet:5th subnet:
Calculating VLSMs (cont.)
A Working VLSM Example
Derived from the 172.16.32.0/20 Subnet
A Working VLSM Example (cont.)
172.16.32.0/26
172.16.32.64/26
172.16.32.128/26
172.16.32.192/26
26 bit mask(62 hosts)
Derived from the 172.16.32.0/20 Subnet
Derived from the 172.16.33.0/26 Subnet
30 bit mask(2 hosts)
172.16.32.0/26
172.16.32.64/26
172.16.32.128/26
172.16.32.192/26
26 bit mask(62 hosts)
Derived from the 172.16.32.0/20 Subnet
A Working VLSM Example (cont.)
172.16.33.0/30
172.16.33.4/30
172.16.33.8/30
172.16.33.12/30
Derived from the 172.16.33.0/26 Subnet
30-Bit Mask(2 Hosts)
172.16.32.0/26
172.16.32.64/26
172.16.32.128/26
172.16.32.192/26
26-Bit Mask(62 Hosts)
Derived from the 172.16.32.0/20 Subnet
A Working VLSM Example (cont.)
Route Summarization
© 2001, Cisco Systems, Inc. 3-14
What Is Route Summarization?
Routing table172.16.25.0/24172.16.26.0/24172.16.27.0/24
172.16.27.0/24
172.16.26.0/24
172.16.25.0/24
A
What Is Route Summarization? (cont.)
• Routing protocols can summarize addresses of several networks into one address
I can route to the 172.16.0.0/16 network.
Routing Table172.16.0.0/16
B
Routing Table172.16.25.0/24172.16.26.0/24172.16.27.0/24
172.16.27.0/24
172.16.26.0/24
172.16.25.0/24
A
Summarizing Within an Octet
172.16.168.0/24 = 10101100 . 00010000 . 10101 000 . 00000000
Number of Common Bits = 21Summary: 172.16.168.0/21
Noncommon Bits = 11
172.16.169.0/24 = 172 . 16 . 10101 001 . 0
172.16.170.0/24 = 172 . 16 . 10101 010 . 0
172.16.171.0/24 = 172 . 16 . 10101 011 . 0
172.16.172.0/24 = 172 . 16 . 10101 100 . 0
172.16.173.0/24 = 172 . 16 . 10101 101 . 0
172.16.174.0/24 = 172 . 16 . 10101 110 . 0
172.16.175.0/24 = 172 . 16 . 10101 111 . 0
Summarizing Addresses in a VLSM-Designed Network
CorporateNetwork
172.16.0.0/16
172.16.64.0/20
172.16.128.0/20
172.16.32.64/26172.16.32.0/24
172.16.128.0/20
172.16.32.128/26
A
B
C
D172.16.64.0/20
ClasslessInterdomain
Routing© 2001, Cisco Systems, Inc. 3-19
Classless Interdomain Routing
• Mechanism developed to alleviate exhaustion of addresses and reduce routing table size• Blocks of Class C addresses assigned
to ISPs—ISPs assign subsets of address space to organizations• Blocks are summarized in routing tables
CIDR Example
ISP
H
B
192.168.8.0/24
192.168.9.0/24
192.168.15.0/24
• Networks 192.168.8.0/24 through 192.168.15.0/24 are summarized by the ISP in one advertisement 192.168.8.0/21
A
192.168.8.0/21
192.168.15.0/24
192.168.8.0/24
192.168.9.0/24
WAN Basics
• A network that serves users across a broad geographic area• Often uses transmission devices provided by public carriers (Pacific Bell, AT&T, etc.) • This service is commonly referred to as
“plain old telephone service” (POTS)•WANs function at the lower three layers of the OSI reference model• Physical layer, data link layer, and network
layer
What Is a WAN?
WAN Overview
Service Provider
• WANs connect sites• Connection requirements vary depending
on user requirements and cost
What is a WAN?
A WAN is a data communications network that covers a relatively broad geographic area and often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.
WAN connection types
• Point-to-Point Links or Leased Lines• Circuit Switching• Packet Switching
Point-to-Point Links or Leased Lines
• A point-to-point link is also known as a leased line because its established path is permanent and fixed for each remote network reached through the carrier facilities.
Leased Line
• One connection per physical interface• Bandwidth: depends on interface type• Cost effective at 4–6 hours daily usage• Dedicated connections with predictable throughput• Permanent• Cost varies by distance
• Dedicated physical circuit established, maintained, and terminated through a carrier network for each communication session• Datagram and data stream transmissions• Operates like a normal telephone call• Example: ISDN
WANModem Modem
Circuit Switching
•Sets up line like a phone call. No data can transfer before the end-to-end connection is established.
•Uses dial-up modems and ISDN. It is used for low-bandwidth data transfers.
Circuit Switching
POTS Using Modem Dialup
• Widely available• Easy to set up• Dial on demand• Asynchronous transmission• Low cost, usage-based• Lower bandwidth access requirements
Telecommuters
Mobile Users
ModemCorporate Network
ServerModem
Access Router
Basic Telephone
Service
Integrated Services Digital Network (ISDN)
• High bandwidth•Up to 128 Kbps per basic rate interface • Dial on demand•Multiple channels• Fast connection time•Monthly rate plus cost-effective,
usage-based billing• Strictly digital
LAN Server
Company Network
Telecommuter/After-Hours, Work-at-Home
BRI2B+D
BRI/PRI23B+D
30B+D (Europe)
ISDN
• Network devices share a point-to-point link to transport packets from a source to a destination across a carrier network• Statistical multiplexing is used to enable devices to share
these circuits• Examples: ATM, Frame Relay, X.25
WANModem Modem
Multiplexing Demultiplexing
Packet Switching
•WAN switching method that allows you to sharebandwidth with other companies to save money.
•Think of packet switching networks as a party line. As long as you are not constantly transmit-ting data and are instead using bursty data transfers, packet switching can save you a lot of money. However, if you have constant data transfers,then you will need to get a leased line.
• Frame Relay and X.25 are packet-switching technologies. Speeds can range from 56Kbps to 2.048Mbps.
Packet Switching
Frame Relay
• Permanent, not dialup• Multiple connections per
physical interface (permanent virtual circuits)
• Efficient handling of bursty (peak performance period) data
• Guaranteed bandwidth (typical speeds are 56/64 Kbps, 256 Kbps, and 1.544 Mbps)—committed information rate (CIR)
• Cost varies greatly by region
Permanent Virtual Circuit (PVC)
X.25
• Very robust protocol for low-quality lines• Packet-switched• Bandwidth: 9.6 kbps–64 kbps• Well-established technology;
large installed base• Worldwide availability
X.25DCE
DTE DTEDCE
Asynchronous Transfer Mode (ATM)
• Technology capable of transferring voice, video, and data through private and public networks
• Uses VLSI technology to segment data, at high speeds, into units called cells• 5 bytes of header information• 48 bytes of payload• 53 bytes total
• Cells contain identifiers that specify the data stream to which they belong
• Primarily used in enterprise backbones or WAN links
DataDataHeaderHeader
55 4848
Cabling the WAN
Core_Server
core_sw_a
ISDN Cloud
LegendFastEthernet/EthernetISDNDedicated
core_sw_b core_sw_b
ISL
Leased Line/Frame Relay
WAN Physical Layer Implementations
• Physical layer implementations vary• Cable specifications define speed of link
PPP
Fram
e R
elay
EIA/TIA-232EIA/TIA-449
X.21 V.24 V.35HSSI
ISDN BRI (with PPP)
RJ-45NOTE: Pinouts are different than RJ-45
used in campus
HD
LC
Differentiating Between WAN Serial Connectors
Router connections
Network connections at the CSU/DSUEIA/TIA-232 EIA/TIA-449 EIA-530V.35 X.21
CSU/DSU
End user device
DTE
DCE
Service provider
Data Terminal EquipmentEnd of the user’s deviceon the WAN link
Data Communications Equipment• End of the WAN provider’s
side of the communication facility• DCE is responsible for clocking
DCEDTE
ModemCSU/DSU
S S
SSS S
DTE DTEDCE DCE
Serial Implementation ofDTE versus DCE
WAN Terminating Equipment
Modem
Data Terminal EquipmentDTE
Data Circuit-Terminating Equipment
The Service Providers The Service Providers EquipmentEquipment
DCE
EIA/TIA-232V.35X.21HSSI
To Corporate Network
The Customer’s The Customer’s EquipmentEquipment
WAN Provider(Carrier) Network
Physical Cable Types
Usually on the Customer’sPremises
Router
LAN/WAN Devices
© 1999, Cisco Systems, Inc. www.cisco.com
• Hubs
• Bridges
• Switches
• Routers
LAN/WAN Devices
Hub
• Device that serves as the center of a star Device that serves as the center of a star topology network, sometimes referred to topology network, sometimes referred to as a as a multiport repeatermultiport repeater, , no forwarding no forwarding intelligenceintelligence
Hubs123123
124124
125125
126126
127127
128128
Hub
DataData DataData
• Amplifies signals• Propagates signals through the network• Does not filter data packets based on destination• No path determination or switching• Used as network concentration point
Hubs Operate at Physical layer
A B C D
Physical
• All devices in the same collision domain• All devices in the same broadcast domain• Devices share the same bandwidth
Hubs: One Collision Domain
• More end stations means more collisions• CSMA/CD is used
Bridge
• Device that connects and passes packets Device that connects and passes packets between two network segments.between two network segments.
• More intelligent than hub—analyzes More intelligent than hub—analyzes incoming packets and forwards (or filters) incoming packets and forwards (or filters) them based on addressing information. them based on addressing information.
Bridge
Segment 1 Segment 2
123123
124124
125125
126126
127127
128128Corporate Intranet
Hub Hub
• More intelligent than a hub—can analyze incoming packets and forward (or filter) them based on addressing information• Collects and passes packets between two network segments • Maintains address tables
Bridge Example
Switches
• Use Use bridging technologybridging technology to to forward traffic between ports. forward traffic between ports.
• Provide full Provide full dedicateddedicated data transmission data transmission rate between two stations that are directly rate between two stations that are directly connected to the switch ports.connected to the switch ports.
• Build and maintain Build and maintain address address tablestables called content-addressable memory called content-addressable memory (CAM).(CAM).
10-MbpsUTP Cable
“Dedicated”
Workstation
3131
Switch
Corporate Intranet
3232
33 3636100 Mbps 100 Mbps
• Uses bridging technology to forward traffic (i.e. maintains address tables, and can filter)
• Provides full dedicated transmission rate between stations that are connected to switch ports
• Used in both local-area and in wide-area networking• All types available—Ethernet, Token Ring, ATM
Switching—“Dedicated” Media
3535
3434
• Each segment has its own collision domain• All segments are in the same broadcast domain
Data Link
Switches and Bridges Operate at Data Link Layer
OR1 2 3 1 24
Switches
• Each segment has its own collision domain• Broadcasts are
forwarded to all segments
Memory
Switch
Routers• Interconnect LANs and WANsInterconnect LANs and WANs• Provide path determination using metricsProvide path determination using metrics• Forward packets from one network to Forward packets from one network to
anotheranother• Control broadcasts to the networkControl broadcasts to the network
Routing TableNET INT Metric
124
S0S0E0
100
1.0 4.0
1.3E0
4.3S0
2.2
E0
2.1
S0
4.1
4.2
1.1
1.2
Routing TableNET INT Metric
124
E0S0S0
001
• Logical addressing allows for hierarchical network• Configuration required• Uses configured information to identify paths to networks
Network Layer Functions (cont.)
Routers: Operate at the Network Layer
• Broadcast control
• Multicast control
• Optimal path determination
• Traffic management
• Logical addressing
• Connects to WAN services
Using Routers to Provide Remote Access
Internet
Telecommuter
Branch Office
Modem or ISDN TA
Mobile User
Main Office
Network Device Domains
Hub Bridge Switch Router
Collision Domains:1 4 4 4
Broadcast Domains:1 1 1 4