instructor & todd lammle
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Sybex CCNA 640-802 Chapter 14: Wide Area Networks
Instructor & Todd Lammle
Chapter 14 Objectives
The CCNA Topics Covered in this chapter include:
• Introduction to WAN’s• HDLC• PPP• Frame Relay• Introduction to VPN’s
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Defining WAN Terms
• Customer Premises Equipment (CPE)
• Demarcation (demarc)
• Local loop
• Central Office (CO)
• Toll network
WAN Connection Types
DTE-DCE-DTE
Channel Service Unit (CSU) is a device that converts a digital data frame from the communications technology used on a local area network (LAN) into a frame appropriate to a wide-area network (WAN) and vice versa. The Data Service Unit (DSU) is a device that performs protective and diagnostic functions for a telecommunications line.
WAN Support
• Frame Relay• ISDN: Integrated Services Digital
Network• LAPB: Link Access Procedure,
Balanced• LAPD: Link Access Procedure, D-
channel• HDLC: High-level Data Link Control• PPP• ATM: Asynchronous Transfer Mode
HDLC Protocol
• Bit-oriented Data Link layer ISO standard protocol, i.e., control information is encoded by bits
• Specifies a data encapsulation method on synchronous serial data links
• A point-to point protocol used on leased lines
• No authentication can be used
HDLC Frame Format
Point-to-Point Protocol (PPP)
• Purpose:– Transport layer-3 packets across a
Data Link layer point-to-point link
• Can be used over asynchronous serial (dial-up) or synchronous serial (ISDN) media– Uses Link Control Protocol (LCP)
• Builds & maintains data-link connections
Point-to-Point Protocol Stack
PPP Main Components
• EIA/TIA-232-C– Intl. Std. for serial communications
• HDLC– Serial link datagram encapsulation method
• LCP– Used in P-t-P connections:
• Establishing• Maintaining• Terminating
• NCP– Method of establishing & configuring Network
Layer protocols– Allows simultaneous use of multiple Network
layer protocols
LCP Configuration Options
• Authentication– PAP: Password Authentication Protocol– CHAP: Challenge Handshake
Authentication Protocol• Compression
– Stacker– Predictor
• Error detection– Quality– Magic Number
• Multilink– Splits the load for PPP over 2+ parallel
circuits; a bundle
PPP Session Establishment
• Link-establishment phase
• Authentication phase
• Network-layer protocol phase
PPP Session Establishment
PPP Authentication Methods
• Password Authentication Protocol (PAP)– Passwords sent in clear text– Remote node returns username & password– Only performed in initial link establishment
• Challenge Handshake Authentication Protocol (CHAP)– Done at start-up & periodically– Challenge & Reply
• Remote router sends a one-way hash ~ MD5
Configuring PPP• Step #1: Configure PPP on RouterA & RouterB:
Router__#config t
Router__(config)#int s0
Router__(config-if)#encapsulation ppp
Router__(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 remoteremote router
(2) Passwords must match
• Step #3: Choose Authentication type for each router; CHAP/PAP
Router__(Config)#int s0
Router__(config-if)#ppp authentication chap
Router__(config-if)#ppp authentication pap
Router__(config-if)#^Z
PPP Example 1
PPP Example 2: Failed PPP authentication
PPP Example 3:Mismatched WAN Encapsulations
PPP Example 4:Mismatched IP Address
Frame Relay
• Background– High-performance WAN encapsulation
method– OSI Physical & data Link layer– Originally designed for use across ISDN
• Supported Protocols– IP, DECnet, AppleTalk, Xerox Network
Service (XNS), Novell IPX, Banyan Vines, Transparent Bridging, & ISO
Before Frame Relay
After Frame Relay
Frame Relay
• Purpose– Provide a communication interface
between DTE & DCE equipments– Connection-oriented Data Link
layer communication• Via virtual circuits: PVC, SVC• Provides a complete path from the
source to destination before sending the first frame
Frame Relay Terminology
Frame Relay Encapsulation
• Specified on serial interfaces• Encapsulation types:
– Cisco (default encapsulation type)– IETF (used between Cisco & non-
Cisco devices)
RouterA(config)#int s0
RouterA(config-if)#encapsulation frame-relay ?
ietf Use RFC1490 encapsulation
<cr>
Data Link Connection Identifiers (DLCIs)
• Frame Relay PVCs are identified by DLCIs• IP end devices are mapped to DLCIs
– Mapped dynamically or mapped by IARP
• Global Significance: – Advertised to all remote sites as the same PVC, need
LMI extensions
• Local Significance: – DLCIs do not need to be unique
• ConfigurationRouterA(config-if)#frame-relay interface-dlci ?
<16-1007> Define a DLCI as part of the current
subinterface
RouterA(config-if)#frame-relay interface-dlci 16
DLCI’s are Locally Significant
Local Management Interface (LMI)
• Background: a signaling standard between a router and the first connected frame relay switch
• Purpose: passing information about the operation and status of the VC between the DTE and switch
• LMI Messages– Keepalives– Multicasting– Global addressing– Status of virtual circuits
LMI Types
• Configuration:RouterA(config-if)#frame-relay lmi-type ? cisco ansi q933a
– Beginning with IOS ver 11.2+ the LMI type is auto-sensed
– Default type: cisco• Virtual circuit status:
– Active: everything is up, routers can exchange information
– Inactive: router interface is up and connected with the switch, but the remote router is not up
– Deleted: no LMI info is being received on the interface from the switch
Single interfacesRouterA(config)#int s0/0
RouterA(config-if)#encapsulation frame-relay
RouterA(config-if)#ip address 172.16.20.1 255.255.255.0
RouterA(config-if)#frame-relay lmi-type ansi
RouterA(config-if)#frame-relay interface-dlci 101
RouterA(config-if)#^Z
Sub-interfaces
• Definition– Multiple virtual circuits on a single
serial interface: multiplexing– Enables the assignment of different
network-layer characteristics to each sub-interface
• IP routing on one sub-interface• IPX routing on another
– Mitigates difficulties associated with:• Partial meshed Frame Relay networks• Split Horizon protocols
Creating Sub-interfaces
Configuration:#1: Set the encapsulation on the serial
interface
#2: Define the subinterfaceRouterA(config)#int s0
RouterA(config)#encapsulation frame-relay
RouterA(config)#int s0.?
<0-4294967295> Serial interface number
RouterA(config)#int s0.16 ?
multipoint Treat as a multipoint link
point-to-point Treat as a point-to-point link
Sub-interfaces
– Point-to-point: a single virtual circuit connects one router to another. Each p-t-p subinterface requires its own subnet.
– Multipoint: when the router is the center of a star of virtual circuits that are using a single subnet for all routers’ serial interfaces connected to the switch.
Mapping Frame Relay
Necessary to IP end devices to communicate– Addresses must be mapped to
the DLCIs– Methods:
• Frame Relay map command• Inverse-arp function
Using the map command
RouterA(config)#int s0
RouterA(config-if)#encap frame
RouterA(config-if)#int s0.16 point-to-point
RouterA(config-subif)#no inverse-arp
RouterA(config-subif)#ip address 172.16.30.1 255.255.255.0
RouterA(config-subif)#frame-relay map ip 172.16.30.17 16 ietf broadcast
Using the inverse arp command
RouterA(config)#int s0.16 point-to-point
RouterA(config-subif)#encap frame-relay ietf
RouterA(config-subif)#ip address 172.16.30.1 255.255.255.0
RouterA(config-subif)#frame-relay interface-dlci 200
Committed Information Rate (CIR)
• Definition: Provision allowing customers to purchase amounts of bandwidth lower than what they might need– Cost savings– Good for bursty traffic– Not good for constant amounts of
data transmission
Congestion Control• Discard Eligibility (DE):
– Transmit packets beyond the CIR, the packets exceeding the CIR are to be discarded if network is congested at that time. These excessive bits are marked with a DE bit.
• Forward-Explicit Congestion Notification (FECN)– When the frame relay network recognizes
congestion in the cloud, the FECN bit will be set to 1 to notify the destination DTE that the path the frame just traversed is congested.
• Backward-Explicit Congestion Notification (BECN)– When the switch detects congestions, it’ll set the
BECN bit in a frame that’s destined for the source router.
Monitoring Frame Relay
RouterA>sho frame ?
ip show frame relay IP statistics
lmi show frame relay lmi statistics
map Frame-Relay map table
pvc show frame relay pvc statistics
route show frame relay route
traffic Frame-Relay protocol statistics
RouterA#sho int s0
RouterB#show frame map
Router#debug frame-relay lmi
Troubleshooting Frame Relay
Why can’t RouterA talk to RouterB?Why can’t RouterA talk to RouterB?You need to use your own DLCI number 100 instead of the remoteYou need to use your own DLCI number 100 instead of the remoteDLCI number to communicate with the switch. DLCI number to communicate with the switch.
Troubleshooting Frame Relay
Why is RIP not sent across the PVC?Why is RIP not sent across the PVC?Because frame relay is a non-broadcast multi-access network, i.e., no Because frame relay is a non-broadcast multi-access network, i.e., no broadcast across the PVC. So it’s necessary to add broadcast in the broadcast across the PVC. So it’s necessary to add broadcast in the mapping statement.mapping statement.
Introduction to VPN’s
• VPNs are used daily to give remote users and disjointed networks connectivity over a public medium like the Internet instead of using more expensive permanent means.
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Types of VPN’s
• REMOTE ACCESS VPNSRemote access VPNs allow remote users like
telecommuters to securely access the corporate network wherever and whenever they need to.
• SITE-TO-SITE VPNSSite-to-site VPNs, or, intranet VPNs, allow a company to
connect its remote sites to the corporate backbone securely over a public medium like the Internet instead of requiring more expensive WAN connections like Frame Relay.
• EXTRANET VPNSExtranet VPNs allow an organization’s suppliers,
partners, and customers to be connected to the corporate network in a limited way for business-to-business (B2B) communications.
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Written Labs and Review Questions
– Open your books and go through all the written labs and the review questions.
– Review the answers in class.
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