Chapter 11

Wide Area Networking (WAN) Protocols

Defining WAN Terms

Customer Premises Equipment (CPE) is your stuff

Demarcation (demarc) is end of provider’s responsibility

Local loop connects demarc to central office

Central Office (CO) / Point of Presence (POP) connects customer to provider’s switching network

Toll network - trunk lines in WAN network

WAN Connection Types

Up to 45 Mbps

WAN Support

Frame Relay – packet switched, 64 Kbps to 1.44 Mbps

ISDN – voice and data over phone lines LAPB – connection oriented, good with errors,

not used much HDLC - connection oriented, proprietary PPP – standard protocol, very flexible ATM – simultaneous transmission of voice, video

and data, uses 53 byte sized cells for sending.

Serial Transmission

Cisco routers use a proprietary 60-pin serial connector

Serial links are described in frequency or cycles-per-second

Amount of data carried inside a frequency is the bandwidth– Bits-per-second that a serial line can carry

DCE/DTE Equipment

DTE (Data Terminal Equipment)– Routers are (usually) DTEs

DCE (Data Communication Equipment)– CSU/DSUs are the DCEs

HDLC Protocol

“High Level Data Link Control” Bit-oriented Data Link layer ISO standard

protocol Specifies a data encapsulation method Point-to-Point protocol for leased lines No authentication can be used Different HDLC versions incompatible

HDLC Frame Format

Point-to-Point Protocol (PPP)

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 - standard for serial communications HDLC - serial link datagram encapsulation method LCP - used in Point-to-Point connections:

– Establishing– Maintaining– Terminating

NCP– Establishes & configures Network Layer protocols– Allows simultaneous use of multiple Network layer protocols

LCP Configuration Options

Authentication identifies the user; PAP and CHAP Compression helps speed transfers; Stacker and

Predictor Error detection; Quality and Magic Number Multilink splits the load for PPP over 2+ parallel

circuits (a bundle)

PPP Session Establishment

Link-establishment phase – LCP packets test the link

Authentication phase (if configured) – PAP or CHAP do their stuff

Network layer protocol phase – PPP uses Network Control Protocol to encapsulate other protocols

PPP 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

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

Frame Relay

Background– High-performance WAN encapsulatuon 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

Frame Relay

Provide a communications interface between DTE & DCE equipment

Connection-oriented Data Link layer communication– Via virtual circuits– 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 (choose one):

– 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 Local Significance:

– DLCIs do not need to be unique Configuration

RouterA(config-if)#frame-relay interface-dlci ?<16-1007> Define a DLCI as part of the current

subinterfaceRouterA(config-if)#frame-relay interface-dlci 16

Local Management Interface (LMI)

Adds to frame relay Allows routers to talk to frame switch LMI messages from router to switch:

– Keepalives (is data flowing?)– Multicasting (DLCI PVCs)– Multicast addressing (global significance)– Status of DLCI virtual circuits

LMI Types

Three types of LMI:RouterA(config-if)#frame-relay lmi-type ? cisco ansi q933a

– LMI type is auto-sensed beginning with IOS 11.2+– Default type: cisco

Virtual circuit status:– Active – routers are routing– Inactive – router is up, remote router is not– Deleted – no LMI info is being received

Sub-interfaces

Multiple virtual circuits on a single serial interface

Allows different network-layer characteristics for each sub-interface

– IP routing on one sub-interface– IPX routing on another

Reduces difficulties associated with:– Partial meshed Frame Relay networks– Split Horizon protocols

Partial Meshed Networks

This works on a LAN, but is messy with WANs

Have to set up PVCs for frame relay

Full Mesh Networks

This works on LANs and WANs, but is very expensive

Each circuit is a separate cost

Partial Mesh w/ Subinterfaces

A, B, and C are fully meshed

C and D are point to point

D and E are point to point

C and D have subinterfaces to forward packets

Creating Sub-interfaces

#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

Mapping Frame Relay

Necessary for 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-if)#no inverse-arp

RouterA(config-if)#ip address 172.16.30.1 255.255.255.0

RouterA(config-if)#frame-relay map ip 172.16.30.17 16 ietf broadcast

RouterA(config-if)#frame-relay map ip 172.16.30.18 17 broadcast

RouterA(config-if)#frame-relay map ip 172.16.30.19 18

See page 552 for full explanation

Using inverse arp command

RouterA(config)#int s0.16 point-to-point

RouterA(config-if)#encap frame-relay ietf

RouterA(config-if)#ip address 172.16.30.1 255.255.255.0

Congestion Control

What if frame relay circuit gets too busy? Discard Eligibility (DE) drops packets that are eligible Forward-Explicit Congestion Notification (FECN)

alerts destination DCE that circuit is busy Backward-Explicit Congestion Notification (BECN)

alerts source router to slow down

Committed Information Rate (CIR)

Allows customers to purchase amounts of bandwidth lower than what they might need

CIR is guaranteed rate, extra traffic is not guaranteed– Cost savings– Good for bursty traffic– Not good for constant amounts of data transmission

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

ISDN

Integrated Services Digital Network– Used by Telecoms to simultaneously send voice,

data, and music, etc. over current phone lines– Uses PPP typically

ISDN

Uses BRI (Basic Rate Interface)– 2-64 K channels for data– 1-16 K signaling channel

Uses terminals– TE1 – Understand ISDN standards– TE2 – predate standards and use an adapter– NT1 – converts 4-wire to 2-wire ISDN– NT2 – Switch or PBX (rare)– TA – adapter for ISDN

BRI

Basic Rate Interface– Operates at 64 Kbps– Total bandwidth for ISDN BRI is 144 Kbps (64x2 and 16)

In NA and Japan, have PRI (Primary Rate Interface)– Operates at 1.544 Kbps (23x64 and 64)

In Europe and AUstralia, have PRI (Primary Rate Interface)

– Operates at 2.048 Kbps (30x64 and 64)

DDR

Dial-On-Demand Routing– As needed basis– Need the equipment in order to run