Foundation Summary

Last Updated on Wed, 28 Jun 2023 | CCIE Security

The "Foundation Summary" is a condensed collection of material for a convenient review of this chapter's key concepts. If you are already comfortable with the topics in this chapter and decided to skip most of the "Foundation Topics" material, the "Foundation Summary" will help you recall a few details. If you just read the "Foundation Topics" section, this review should help further solidify some key facts. If you are doing your final preparation before the exam, the "Foundation Summary" offers a convenient and quick final review.

Table 1-18 OSI Model

OSI Name and Layer Number

Description

Application layer (Layer 7)

The application layer is closest to the end user, which means that the application is being accessed by the end user. This layer's major function is to provide services to end users. Examples of application layer services include the following:

• File Transfer Protocol

• Trace route

• Mail clients

Presentation layer (Layer 6)

The presentation layer handles data formats and code formatting. This layer's functions are normally transparent to the end user because it takes care of code formats and presents them to the application layer, where the end user can examine the data. Examples of presentation layer protocols include the following:

• HTML

continues continues

Table 1-18 OSI Model (Continued)

OSI Name and Layer Number

Description

Session layer (Layer 5)

The session layer performs several major functions, including managing sessions between devices and establishing and maintaining sessions. Examples of session layer protocols include the following:

• Database SQL

• NetBIOS Name Queries

• H.323

Transport layer (Layer 4)

The transport layer is responsible for segmenting upper-layer applications and establishing end-to-end connections between devices. Other transport layer functions include providing data reliability and error-free delivery mechanisms. Information being processed at this layer is processed in what are commonly known as segments. Examples of transport layer protocols include Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Voice RTP resides here also.

Network layer (Layer 3)

The network layer determines the best path to a destination. Device addressing, packet fragmentation, and routing all occur at the network layer. Information at this layer is processed in what are commonly known as packets. Examples of network layer protocols include the following:

• Internet Protocol (IP)

• Open Shortest Path First (OSPF)

• Cisco Enhanced Interior Gateway Routing Protocol (EIGRP)

Data link layer (Layer 2)

The data link layer focuses on getting data reliably across any particular kind of link. Flow control and error notifications are other data link layer functions. The data link layer applies to all access methods, whether they are LAN or WAN methods. Information being processed at this layer is processed in what are commonly known as frames. Examples of correct frame types include the following:

• Frame Relay

• Bridge protocol data units (spanning tree)
Table 1-18 OSI Model (Continued)

OSI Name and Layer Number

Description

Physical layer (Layer 1)

The physical layer consists of standards that describe bit ordering, bit transmission rates, connector types, and electrical and other specifications. Information at Layer 1 is transmitted in binary (1s and 0s; for example, the letter A is transmitted as 00001010). Examples of physical layer standards include the following:

• Gigabit Ethernet
Table 1-19 Ethernet Media Formats

Media Type

Characteristics

10BASE5*

• Maximum length: 500 m

• Maximum stations: 1024

• Minimum distance between devices: 2.5 m

10BASE2

• Maximum length: 185 m, using RG58 cable types and T connectors on all end stations

• Minimum distance between devices: 0.5 m

• Maximum devices per 185 m segment: 30 stations

• Speed: 10 Mbps

10BASE-T

• Based on UTP cabling

• Up to 100 m; better-category cables longer

• One device per cable; typically, only one device per segment with hubs or switches connecting all devices together

• Physical topology: star

• Logical topology: bus
Table 1-19 Ethernet Media Formats (Continued)

Media Type

Characteristics

100BASE-T

• Same characteristics as 10BASE-T but operates faster, at 100 Mbps

• Can be fiber, as well (100BASE-FX); defined in IEEE 802.3U

• Physical topology: star

• Logical topology: bus

1000 GE

• Gigabit Ethernet operating at 1000 Mbps

• Can run over fiber or UTP; frame formats and CSMA/CD identical to Ethernet standards

• Physical topology: star

• Logical topology: bus

*The word BASE refers to baseband signaling, which uses a single channel, as opposed to broadband, which uses multiple frequency channels.

*The word BASE refers to baseband signaling, which uses a single channel, as opposed to broadband, which uses multiple frequency channels.

■ All ports part of FEC must be set to the same speed.

■ All ports must belong to the same VLAN.

■ Duplex must be the same (half or full), not a mixture.

■ Up to eight ports can be bundled together.

■ To set FEC on a switch, the CatOS syntax is set port channel.

■ To set Fast EtherChannel on a router, the Cisco IOS syntax is channel-group under the Fast Ethernet interface.

Table 1-20 The States of Spanning Tree

Bridge Port State

Description

Disabled

The port is not participating in spanning tree and is not active.

Listening

The port has received data from the interface and will listen for frames. In this state, the bridge only receives data; it does not forward any frames to the interface or to other ports.

Learning

The bridge still discards incoming frames. The source address associated with the port is added to the CAM table. BPDU are sent and received.

Forwarding

The port is fully operational; frames are sent and received.

Blocking

The port has been through the learning and listening states, and because this particular port is a dual path to the root bridge, the port is blocked to maintain a loop-free topology.
Table 1-21 Class A, B, C, D, and E Ranges*

Class of Address

Starting Bit Pattern

Range

Default Subnet Mask

Class A

Oxxxxxxx

l-l26, l27**

255.0.0.0

Class B

lOxxxxxx

l28-l9l

255.255.0.0

Class C

llOxxxxx

l92-223

255.255.255.0

Class D

lllOxxxx

224-239

Not officially defined

Class E

llllxxxx

240-255

Reserved

*Only Class A, B, and C have predefined default subnet masks.

**127.0.0.0 is reserved for loopback purposes. Other reserved addresses for private use as defined by RFC 1918 are as follows:

172.16.0.0-172.31.255.255

192.168.0.0-192.168.255.255

*Only Class A, B, and C have predefined default subnet masks.

**127.0.0.0 is reserved for loopback purposes. Other reserved addresses for private use as defined by RFC 1918 are as follows:

172.16.0.0-172.31.255.255

192.168.0.0-192.168.255.255

Table 1-22 Routing Protocol Classifications

Routing Protocol

Class

IGRP

Distance vector (classful)

EIGRP

Hybrid (classless)

OSPF

Link-state (classless)

RIPvl

Distance vector (classful)

RIPv2

Distance vector (classless)

BGP

Path vector (classless)
Table 1-23 TCP Flags Summary

Flag

Description

URG (U)

Urgent—Informs the other station that urgent data is being carried. The receiver will decide what to do with the data.

ACK (A)

Acknowledge—Indicates that the packet is an acknowledgment of received data, and the acknowledgment number is valid.

PSH (P)

Push—Informs the end station to send data to the application layer immediately.

RST (R)

Reset—Resets an existing connection.

SYN (S)

Synchronize—Initiates a connection.

FIN

Finished—Indicates that the sender is finished sending data and terminates the session.
Table 1-24 TCP/IP Common Applications

Application

Description

Address Resolution Protocol (ARP)

Maps an IP address to a MAC address.

Reverse Address Resolution Protocol (RARP)

Determines a host's IP address when the MAC address is known.

Dynamic Host Configuration Protocol (DHCP)

Dynamically provides IP addresses to TCP/IP hosts, subnet masks, and gateway addressing. Many other IP options can be assigned, as well.

Hot Standby Router Protocol (HSRP)

Redundancy gateway protocol, Cisco proprietary.

Internet Control Message Protocol (ICMP)

A network layer (Layer 3) Internet protocol that reports errors and provides other information relevant to IP packet processing. ICMP is fully documented in RFC 792.

Telnet

TCP/IP application layer protocol that enables remote management of TCP/IP hosts, such as routers or switches.

File Transfer Protocol (FTP)

TCP/IP application layer protocol that enables file transfer between TCP/IP hosts using a TCP, connection-orientated protocol.

Trivial File Transfer Protocol (TFTP)

TCP/IP application layer protocol that enables file transfers between TCP/IP hosts using a UDP, connectionless protocol.
Table 1-25 Default Administrative Distances

Route Source

Default Administrative Distance

Connected interface

0

Static route

1

EIGRP summary route

5

External BGP

20

Internal EIGRP

90

IGRP

100

OSPF

110

IS-IS

115

RIP

120

EGP

140

EIGRP external route

170

Internal BGP

200

Unknown

255
Table 1-26 Common TCP/UDP Ports in VoIP

Related Posts

Application

Protocol

Port(s)

DHCP

UDP

67/68

HTTP

TCP

80

RTP

UDP

16384-32767

TAPI/JTAPI (Softphone if present)

TCP

2748

Cisco Softphone Directory Lookup

TCP

389/8404

Cisco skinny

TCP

2000

HIDS management

TCP

5000

Directory access (DCD)

TCP

8404

Continue reading here: Scenario Routing IP on Cisco Routers

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