1

Wide Area Network

(WAN)

2 Content

Remote access overview WAN Concepts WAN Configurations Point-to-point WANs Fundamentals of WANs Frame Relay Concepts, Config and Troubleshooting Virtual Private Networks IPv6 NAT/PAT

3 Remote Access Overview

A WAN is a data communications network covering a relatively broad geographical area.

A network administrator designing a remote network must weight issues concerning users needs such as bandwidth and cost of the variable available technologies.

4 Circuit switching is a methodology of implementing a

telecommunications network in which two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session.

Packet-switched networks move data in separate, small blocks -- packets -- based on the destination address in each packet. When received, packets are reassembled in the proper sequence to make up the message.

5 PSTN

PSTN – Public Switched Telephone Network Phone Lines – switched meaning you can place a call, at will, to

other destinations. The cable linking your house to exchange is called the Local Loop. Designed for voice, analogue transmissions are used over the local

loop. Telco's will then use high speed digital lines to interconnect exchanges.

This digital signal is sampled and converted using Pulse Code Modulation (PCM). This is demodulated at the other end, and analogue signal transported over local loop to receiving end.

6 PSTN

Lines can be leased, or run through the voice network. Two methods of connection each with advantages and

disadvantages. Modem DSL

7 Modems

Messages from your PC are sent digitally to a device that will translate to Analogue signal.

This is done in a process called modulation. The reverse (Analogue to Digital) is a process called

demodulation. The device is called a modem

8 Modems & CSU/DSU

Dial-up is referred to as a switched circuit as you can hang up and dial another number to establish a different circuit.

Modems are asynchronous, they do not maintain timing Leased Lines with CSU/DSU are synchronous, attempting to keep

in time with other units.

9 Digital Subscriber Line

Digital Subscriber Line (DSL) established in the mid-late 90’s to address issues with modem communication, but still use local loop.

Digital data is sent using a different frequency than voice data – allowing both to be in use at the same time.

No signal/dial – “Always On” access.

10 DSL

Equipment required: Home end

Filter (splitting voice/data) DSL Modem (that matches telco specification)

Telco end DSL Access Multiplexor (DSLAM)

Voice frequency is up to 4000 Hz Data frequency is > 4000 Hz

11 DSL

Types of DSL Asymmetric DSL

Upload and download rates can be different. Symmetric DSL

Upload and download rates are the same Asymetric DSL Types:

ADSL (Asymmetric), VDSL (Very-high-data-rate), CDSL (Consumer). Symetric DSL

SDSL (Symetric), HDSL (high-data-rate), IDSL (ISDN DSL)

12 DSL

Considerations Distance from exchange - < 18,000 ft (5km) Quality of local loop (particularly in old houses/premises) Type of DSL (previous slide) provided by telco Space/Capacity on DLSAM

Speeds can range up to ~10mbps down.

13 Cable Connections

Co-axial cable service – allows data and TV through the same cable (CATV)

No phone line required “Always on” connection. Data and TV (right down to individual TV channels) are separated much

like that of DSL – by individual frequencies.

14 Cable Connections

Speeds 3-6Mbps – but this will depend Shared infrastructure

more local users = slower speeds.

15 WAN Connection Types

16 WAN Connection Types

Packet switching

WAN switching method that allows you to share bandwidth with other companies to save money. As long as you are not constantly transmitting 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.

17 Defining WAN Encapsulation Protocols

Each WAN connection uses an encapsulation protocol to encapsulate traffic while it crossing the WAN link.

The choice of the encapsulation protocol depends on the underlying WAN technology and the communicating equipment.

18 Defining WAN Encapsulation Protocols

Each WAN connection uses an encapsulation protocol to encapsulate traffic while it crossing the WAN link.

The choice of the encapsulation protocol depends on the underlying WAN technology and the communicating equipment.

19 Determining the WAN Type to Use

Availability

Each type of service may be available in certain geographical areas.

Bandwidth

Determining usage over the WAN is important to evaluate the most cost-effective WAN service.

Cost

Making a compromise between the traffic you need to transfer and the type of service with the available cost that will suit you.

20 Determining the WAN Type to Use

Ease of Management Connection management includes both the initial start-up configuration and

the outgoing configuration of the normal operation. Application Traffic

Traffic may be as small as during a terminal session , or very large packets as during file transfer.

21 Max. WAN Speeds for WAN Connections

WAN Type Maximum Speed

Asynchronous Dial-Up 56-64 Kbps

X.25, ISDN – BRI 128 Kbps

ISDN – PRI E1 / T1

Leased Line / Frame Relay E3 / T3

22 OSI Layer-2 Point-to-Point WANs

WAN protocols used on Point-to-Point serial links provide the basic function of data delivery across that one link.

The two most popular data link protocols used today are Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC).

23 High-Level Data Link Control HDLC

HDLC performs OSI Layer-2 functions. It determines when it is appropriate to use the physical medium. Ensures that the correct recipient receives and processes the data that

is sent. Determines whether the sent data was received correctly or not (error

detection).

24 HDLC

HDLC Frame Format

The original HDLC didn’t include any Protocol Type field, every company (including Cisco) added its own field, so it became a proprietary protocol that can be used between only Cisco routers.

25

The Point-to-Point Protocol (PPP) is generally viewed as the successor to the Serial Line IP (SLIP) protocol. PPP provides router-to-router and host-to-network connections over both synchronous and asynchronous circuits.

PPP emerged in the late 1980s in response to a lack of encapsulation protocols for the Internet that was blocking growth of serial-line access. PPP was basically created to solve remote Internet connectivity problems. PPP supports a number of network layer protocols, including Novell IPX, TCP/IP and AppleTalk.

26 The Point to Point Protocol (PPP) is the most widely used Wan protocol and performs the following functions.

Link establishment - This function opens a connection or path between two routers and negotiates how data will be sent across this network path.

Link quality determination - This function will test the link to make sure that the data path is stable and reliable.

Network layer protocol configuration - This function establishes which layer 3 protocols will be sent across the data path. Since PPP can deliver multiple layer 3 protocols such as IP and IPX at the same time both sides of the connection need to know what protocols will be sent.

Link termination - This function will terminate the WAN data path between two routers. With these processes in place data can be moved across a WAN link(s) with reliability using the PPP WAN protocol.

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PPP uses a layered architecture. With its lower-level functions, PPP can use:

• Synchronous physical media like those that connect ISDN.

• Asynchronous physical media like those that use basic telephone service for modem dialup connections.

PPP offers a rich set of services that control setting up a data link. These services are options in LCP and are primarily negotiation and checking frames to implement the point-to-point controls an administrator specifies for the call

With its higher-level functions, PPP carries packets from several network-layer protocols in NCPs.

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PPP runs on the following types of WAN physical interfaces: • Asynchronous serial • ISDN • Synchronous serial PPP datagram transmission employs three key components to provide effective data transmission:Encapsulation - PPP supports the High-Level Data Link Control (HDLC) protocol to provide encapsulation.

Link Control Protocol (LCP) - An extensible LCP is used to establish, configure, and test the data link connection.

Network Control Protocols (NCPs) - a family of NCPs are used to establish and configure different network layer protocols.

29 Point-to-Point Protocol (PPP)

PPP is a standard encapsulation protocol for the transport of different Network Layer protocols (including, but not limited to, IP).

It has the following main functional components

Link Control Protocol (LCP) that establishes, authenticates, and tests the data link connection.

Network Control Protocols (NCPs) that establishes and configure different network layer protocols.

30 Point-to-Point Protocol (PPP)

PPP discards frames that do not pass the error check. PPP is a standard protocol, and so it can be used with all types of routers

(not Cisco Proprietary).

31 PPP LCP Features

Authentication Compression Multilink PPP Error Detection Looped Link Detection

32PPP Authentication Methods Password Authentication Protocol (PAP)

Passwords sent in clear text Remote node returns username & password

Challenge Authentication Protocol (CHAP) Done at start-up & periodically Challenge & Reply

Remote router sends a one-way hash ~ MD5

33 PPP Multilink

PPP Multilink provides load balancing over dialer interfaces-including ISDN, synchronous, and asynchronous interfaces.

This can improve throughput and reduce latency between systems by splitting packets and sending fragments over parallel circuits.

34 Error Detection

PPP can take down a link based on the value of what is called LQM (Link Quality Monitor) as it gets the ratio of corrupted packets to the total number of sent packets, and according to a predetermined value, the link can be brought down if it is thought that its performance is beyond limits accepted.

35 Looped Link Detection

PPP can detect looped links (that are sometimes done by Teleco companies) using what is called Magic Number.

Every router will have a magic number, and if packets were received having the same router’s magic number, then the link is looped.

36Configuring PPP

Step #1: Configure PPP on RouterA & RouterB:

Router__#config tRouter__(config)#int s0Router__(config-if)#encapsulation pppRouter__(config-if)#^Z

Step #2: Define the username & password on each router:

RouterA: RouterA(config)#username RouterB password cisco RouterB: RouterB(config)#username RouterA password cisco

NOTE: (1) Username maps to the remote router (2) Passwords must match

Step #3: Choose Authentication type for each router; CHAP/PAP

Router__(Config)#int s0Router__(config-if)#ppp authentication chapRouter__(config-if)#ppp authentication papRouter__(config-if)#^Z