Wide Area Networking (WAN) Protocols

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Chapter 11

• Wide Area Networking (WAN) Protocols

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Defining WAN Terms

• Customer Premises Equipment (CPE) is your stuff
• Demarcation (demarc) is end of providers
  responsibility
• Local loop connects demarc to central office
• Central Office (CO) / Point of Presence (POP)
  connects customer to providers switching network
• Toll network - trunk lines in WAN network

3
WAN Connection Types
Up to 45 Mbps
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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.

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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

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DCE/DTE Equipment

• DTE (Data Terminal Equipment)
• Routers are (usually) DTEs
• DCE (Data Communication Equipment)
• CSU/DSUs are the DCEs

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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

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HDLC Frame Format
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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

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Point-to-Point Protocol Stack
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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

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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)

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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

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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

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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 remote 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

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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

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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

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Frame Relay Terminology
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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
• ltcrgt

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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 ?
• lt16-1007gt Define a DLCI as part of the current
• subinterface
• RouterA(config-if)frame-relay interface-dlci 16

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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

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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

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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

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Partial Meshed Networks

• This works on a LAN, but is messy with WANs
• Have to set up PVCs for frame relay

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Full Mesh Networks

• This works on LANs and WANs, but is very
  expensive
• Each circuit is a separate cost

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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

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Creating Sub-interfaces

• 1 Set the encapsulation on the serial interface
• 2 Define the subinterface
• RouterA(config)int s0
• RouterA(config)encapsulation frame-relay
• RouterA(config)int s0.?
• lt0-4294967295gt Serial interface number
• RouterA(config)int s0.16 ?
• multipoint Treat as a multipoint
  link
• point-to-point Treat as a point-to-point
  link

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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

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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

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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

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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

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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

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Monitoring Frame Relay

• RouterAgtsho 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
• RouterAsho int s0
• RouterBshow frame map
• Routerdebug frame-relay lmi

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ISDN

• Integrated Services Digital Network
• Used by Telecoms to simultaneously send voice,
  data, and music, etc. over current phone lines
• Uses PPP typically

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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

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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)

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DDR

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