Download Layer Number Layer Designation Function Responsibility Page

Layer
Number
Layer 7
Layer
Designation
Application
Function
Layer 6
Presentation
Presents Data
Handles processing
such as encryption
Layer 5
Session
Keeps different
applications’ data
separate
Layer 4
Transport
Provides reliable or
unreliable delivery
Performs error
correction before
retransmit
Layer 3
Network
Provides logical
addressing, which
routers use for
path determination
Layer 2
Data Link
Combines packets
into bytes and
bytes into frames
Provides access to
media using MAC
address
Performs error
detection not
correction
Provides a User
Interface
File, print,
message,
database, and
application
services
Responsibility
Identifying and establishing the
availability of the intended
communication partner and
determining whether sufficient
resources for the intended
communication exist
Data encryption,
Presents data to the Application
compression, and
layer and is responsible for data
translation
translation and code formatting.
services
Data compression,
decompression, encryption,
decryption are associated with this
layer
Dialog control
Setting up, managing, and then
tearing down sessions between
Presentation layer entities, also
provides dialog control between
devices, or nodes. (Simplex, Half
Duplex, and Full Duplex) Keeps
different applications’ data
separate from other applications’
data
End-to-end
Segments and reassembles data
connection,
into a data stream. (TCP and UDP
TCP Header,
function here) Provides
Upper layer data
mechanisms for multiplexing
upper-layer applications,
establishing sessions, and tearing
down virtual circuits. Also hides
details of any network-dependent
information from higher layers by
providing transparent data
transfer
Routing, IP
Manages device addressing, tracks
header, Data
the locations of devices on the
network, and determines the best
way to move data. Two types of
packets are used at the Network
layer: data and route updates
Framing, LLC
Provides physical transmission of
header, Data, FCS
the data and handles error
notification, network topology,
and flow control. Ensures
messages are delivered to the
proper device on a LAN using
hardware addresses and will
translate messages from the
Network layer into bits for the
Physical layer to transmit. Uses
Media Access Control (MAC) 802.3
and Logical Link Control (LLC)
Page
Number
15
16
16
16
22
24
Layer 1
Physical
Moves bits
between devices
Specifies voltage,
wire speed, and
pin-out of cables
Physical
topology, MAC
header, Data, FCS
802.2
Two functions send bits and
receive bits (communicates with
physical media, cables) The
Physical layer specifies the
electrical, mechanical, procedural,
and functional requirements for
activating, maintaining, and
deactivating a physical link
between end systems
30
Routers 





Routers separate broadcast domains (will not forward any broadcast or multicast packets)
Routers use the logical address in a network layer header to determine the next hop router to forward the
packet to
Routers can use access lists, created by an administrator, to control security on the types of packets that are
allowed to enter or exit an interface
Routers can provide layer 2 bridging functions if needed and can simultaneously route through the same
interface
Layer 3 devices (routers in this case) provide connections between virtual LANs (VLANs)
Routers can provide quality of service (QoS) for specific types of network traffic
Interface Identification –


DTE – Data terminal Equipment – Usually located at the service provider
DCE – Data communication Equipment – the attached device
- Services available to a DTE are most often accessed via modem or channel service unit/data service unit
(CSU/DSU)
Ethernet –


Layer 1 (Physical) and Layer 2 (Data Link)
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
- A protocol that helps devices share the bandwidth evenly without having two devices transmit at the same
time on the network medium
Protocol Data Units (PDUs)




Transport – Segments
- TCP Header
Network – Packets
- IP header
Data Link – Frame
- LLC header
- MAC header
Physical – Bits
TCP/IP Model vs. OSI Model
Process/Application
Application
Presentation
Session
Host-to-Host
Transport
Internet
Network
Network Access
Data Link
Physical
When different protocols in the IP stack are discussed, the layers of the OSI and DoD models are interchangeable.
The TCP/IP Protocol Suite Pg. 70
Process/Application
Trivial File Transfer
Protocol (TFTP)
Host-to-Host
Internet
File Transfer
Protocol
Line Printer
Daemon
Simple Network
Management Protocol
(FTP)
(LPD)
(SNMP)
Simple Mail Transfer
Protocol
Network File
System
X Window
(SMTP)
(NFS)
Telnet
Transmission Control Protocol
User Datagram Protocol
(TCP)
(UDP)
Internet Control
Message Protocol
Address Resolution
Protocol
(ICMP)
(ARP)
Reverse Address Resolution Protocol
(RARP)
Internet Protocol
(IP)
Network Access
Ethernet
Fast Ethernet
Token Ring
FDDI
Key Protocols That Use TCP and UDP Pg. 83
TCP
Port
UDP
Port
Telnet
23
SNMP
161
SMTP
25
TFTP
69
HTTP
80
DNS
53
FTP
21
DNS
53
HTTPS
443
Possible Protocols Found in the Protocol Field of an IP Header Pg. 86
Protocol
Protocol Number
ICMP
1
IP in IP (tunneling)
4
IGRP
9
EIGRP
88
OSPF
89
IPv6
41
GRE
47
Layer 2 Tunnel (L2TP)
115
IP Address Classes Pg. 94
Class
1st Octet
Decimal
Range
1st Octet
High Order
Bits
Network/Host ID
(N=Network, H=Host)
Default Subnet
Mask
Number of
Networks
Hosts per Network
(Usable Addresses)
A
1 – 126*
0
N.H.H.H
255.0.0.0
126 (27 – 2)
16,777,214 (224 – 2)
B
128 – 191
10
N.N.H.H
255.255.0.0
16,382 (214 –
2)
65,534 (216 – 2)
C
192 – 223
110
N.N.N.H
255.255.255.0
2,097,150
(221 – 2)
254 (28 – 2)
D
224 – 239
1110
Reserved for Multicasting
E
240 – 254
1111
Experimental; used for research
Note: Class A addresses 127.0.0.0 to 127.255.255.255 cannot be used and is reserved for loopback and diagnostic
functions.
Class
Private Networks
Subnet Mask
Address Range
A
10.0.0.0
255.0.0.0
10.0.0.0 10.255.255.255
B
172.16.0.0 - 172.31.0.0
255.255.0.0
172.16.0.0 172.31.255.255
C
192.168.0.0
255.255.255.0
192.168.0.0 192.168.255.255
Powers of 2 are important to understand and memorize for use with IP subnetting.
To review powers of 2, remember that when you see a number with another number to its upper right (called an
exponent), this means you should multiply the number by itself as many times as the upper number specifies.
2 power of 1 = 2
2 power of 2 = 4
2 power of 3 = 8
2 power of 4 = 16
2 power of 5 = 32
2 power of 6 = 64
2 power of 7 = 128
2 power of 8 = 256
2 power of 9 = 512
2 power of 10 = 1,024
2 power of 11 = 2,048
2 power of 12 = 4,096
2 power of 13 = 8,192
2 power of 14 = 16,384
CIDR Values
CIDR Classes
CIDR Value
Class A
Class B
Class C
Subnet Mask
Available Host Addresses
/8
255.0.0.0
16777214
/9
255.128.0.0
8388606
/10
255.192.0.0
4194302
/11
255.224.0.0
2097150
/12
255.240.0.0
1048574
/13
255.248.0.0
524286
/14
255.252.0.0
262142
/15
255.254.0.0
131070
/16
255.255.0.0
65534
/17
255.255.128.0
32766
/18
255.255.192.0
16382
/19
255.255.224.0
8190
/20
255.255.240.0
4096
/21
255.255.248.0
2046
/22
255.255.252.0
1022
/23
255.255.254.0
510
/24
255.255.255.0
254
/25
255.255.255.128
126
/26
255.255.255.192
62
/27
255.255.255.224
30
/28
255.255.255.240
14
/29
255.255.255.248
6
/30
255.255.255.252
2
What do we know?
What do we know about a /25?
What do we know about a /26?
What do we know about a /27?
What do we know about a /28?
What do we know about a /29?
What do we know about a /30*?

128 Mask

1 bits on and 7 bits off (10000000)

Block size of 128

2 subnets, each with 126 hosts

192 Mask

2 bits on and 6 bits off (11000000)

Block size of 64

4 subnets, each with 62 hosts

224 Mask

3 bits on and 5 bits off (11100000)

Block size of 32

8 subnets, each with 30 hosts

240 Mask

4 bits on and 4 bits off (11110000)

Block size of 16

16 subnets, each with 6 hosts

248 Mask

5 bits on and 3 bits off (11111000)

Block size of 8

32 subnets, each with 6 hosts

252 Mask

6 bits on and 2 bits off (11111100)

Block size of 4

64 subnets, each with 2 hosts
*Regardless of whether you have a Class A, Class B, or Class C address, the /30 mask will provide you with only two
hosts, ever. This mask is suited almost exclusively – as well as suggested by Cisco-for use on point-to-point links. (WAN)