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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