WAN TECHNOLOGIES
Table of Content
1 WAN technologies overview 2 WAN technologies 3 WAN design
WAN TECHNOLOGIES OVERVIEW
WAN technology
A WAN is a data communications network that operates beyond the geographic scope of a LAN A company or organization must subscribe to an outside WAN service provider in order to use WAN carrier network services
Part of WAN service
Subscriber to Provider Interface
WAN standard: The physical layer
The physical layer protocols describe how to provide electrical, mechanical, operational, and functional connections to the services provided by a communications service provider.
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Datalink Layer
The data link layer protocols define how data is encapsulated for transmission to remote sites, and the mechanisms for transferring the resulting frames.
Data link layer: WAN protocols
Frame Relay: Transmit data very rapidly compared to the other WAN protocols. PPP: Described by RFC 1661, PPP was developed by the IETF. ISDN: Digital services that transmits voice and data over existing phone lines. HDLC: An ISO standard, HDLC might not be compatible between different vendors.
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WAN encapsulation
Flag Header Data FCS Flag
Address Control Protocol
WAN TECHNOLOGIES
Analog dialup
ISDN
Leased line
CSU/DSU
CSU/DSU
Frame Relay
PVC
CSU/DSU CSU/DSU
DSL
Service Download ADSL SDSL HDSL IDSL RADSL CDSL
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Upload 16-640Kbps 1.5442.048Mbps 1.5442.048Mbps 144Kbps
1.544-8.192Mbps 1.544-2.048Mbps 1.544-2.048Mbps 144Kbps
64Kbps-8.192Mbps 16-768Mbps 1Mbps 16-160Kbps
Cable modem
Enhanced cable modems enable two-way, high-speed data transmissions using the same coaxial lines that transmit cable television A cable modem is capable of delivering up to 30 to 40 Mbps of data on one 6 MHz cable channel
POINTTO-POINT
Table of Content
1 Serial Point-to-point links 2 PPP Authentication 3 PPP configuration
SERIAL POINT-TO-POINT LINK
Introduction To Serial Communication
011111100110 ..11110 011111100110 ..11110
Transmission system
Physical medium
Transmission system
WAN technologies are based on serial transmission at the physical layer The signaling methods include Nonreturn to Zero Level (NRZ-L), High Density Binary 3, (HDB3), and Alternative Mark Inversion (AMI).
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Time-division Multiplexing
DTE-DCE
The DCE, commonly a modem or CSU/DSU, is the device used to convert the user data from the DTE into a form acceptable to the WAN service provider transmission link. The DTE-DCE interface for a particular standard defines the following specifications:
Mechanical/physical Number of pins and connector type Electrical Defines voltage levels for 0 and 1 Functional Specifies the functions that are performed by assigning meanings to each of the signaling lines in Procedural Specifies the sequence of events for transmitting data
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DTE-DCE (cont.)
The synchronous serial port on a router is configured as DTE or DCE depending on the attached cable The router end of the shielded serial transition cable may be a DB-60 connector The serial end of the smart serial cable is a 26-pin connector significantly more compact than the DB-60 connector.
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HDLC Encapsulation
HDLC uses synchronous serial transmission providing error-free communication between two points. HDLC defines a Layer 2 framing structure that allows for flow control and error control using acknowledgments and a windowing scheme. Each frame has the same format, whether it is a data frame or a control frame Standard HDLC does not inherently support multiple protocols on a single link The Cisco HDLC frame allows multiple network layer protocols to share the same serial link
HDLC Frame Format
Uses a proprietary data field to support multiprotocol environments
Supports only single-protocol environments
HDLC Encapsulation (cont.)
Configuring HDLC Encapsulation
Enter the interface configuration mode of the serial interface. Then enter the encapsulation hdlc command to specify the encapsulation protocol on the interface. When communicating with a non-Cisco device, synchronous PPP is a more viable option.
Configuring HDLC Encapsulation
Router(config-if)#encapsulation hdlc
Enables HDLC encapsulation Uses the default encapsulation on synchronous serial interfaces
Troubleshooting A Serial Interface
show interfaces serial
Serial x is down, line protocol is down Serial x is up, line protocol is down Serial x is up, line protocol is up (looped) Serial x is up, line protocol is down (disabled) Serial x is administratively down, line protocol is down
PPP AUTHENTICATION
PPP Layered Architecture
PPP uses a layered architecture. A layered architecture is a logical model, design, or blueprint that aids in communication between interconnecting layers. PPP provides a method for encapsulating multiprotocol datagrams over a point-to-point link, and uses the data link layer for testing the connection. PPP is made up of two sub-protocols:
Link Control Protocol Used for establishing the point-to-point link. Network Control Protocol Used for configuring the various network layer protocols.
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PPP Layered Architecture
PPP can carry packets from several protocol suites using NCP. PPP controls the setup of several link options using LCP.
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PPP Layered Architecture (Cont.)
Asynchronous serial Synchronous serial High-Speed Serial Interface (HSSI) Integrated Services Digital Network (ISDN)
PPP Layered Architecture (Cont.)
Authentication Compression Error detection Multilink PPP Callback
PPP Layered Architecture (Cont.)
For every network layer protocol used, a separate Network Control Protocol (NCP) is provided.
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NCP includes functional fields containing
PPP Layered Architecture (Cont.)
Flag Indicates the beginning or end of a frame and consists of the binary sequence 01111110. Address Consists of the standard broadcast address, which is the binary sequence 11111111. Control 1 byte that consists of the binary sequence 00000011, Protocol 2 bytes that identify the protocol encapsulated in the data field of the frame. Data 0 or more bytes
PPP LCP Configuration Options
PPP Session Establishment
Two PPP authentication protocols: PAP and CHAP
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Establishing A PPP Session
Link-establishment frames are used to establish and configure a link. Link-termination frames are used to terminate a link. Link-maintenance frames are used to manage and debug a link.
Establishing A PPP Session: Link-establishment phase
In this phase each PPP device sends LCP frames to configure and test the data link. LCP frames contain a configuration option field that allows devices to negotiate the use of options such as
maximum transmission unit (MTU), compression of certain PPP fields, link-authentication protocol.
If a configuration option is not included in an LCP packet, the default value for that configuration option is assumed This phase is complete when a configuration acknowledgment frame has been sent and received.
Establishing A PPP Session: Authentication phase
Authentication phase (optional) After the link has been established and the authentication protocol decided on, the peer may be authenticated. Authentication, if used, takes place before the network layer protocol phase is entered. LCP also allows for an optional link-quality determination test. The link is tested to determine whether the link quality is good enough to bring up network layer protocols
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Establishing A PPP Session:Network layer phase
In this phase the PPP devices send NCP packets to choose and configure one or more network layer protocols, such as IP. Once each of the chosen network layer protocols has been configured, packets from each network layer protocol can be sent over the link The show interfaces command reveals the LCP and NCP states under PPP configuration
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PPP Authentication Protocols
Passwords sent in clear text Peer in control of attempts
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Challenge Handshake Authentication Protocol
Hash values, not actual passwords, are sent across link. The local router or external server is in control of attempts.
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PPP Authentication Protocols:CHAP Operation
Sydney Challenge Username Sysney Melbourne MD5 Hash # Password cisco sanhinoon Hongkong
Sydney Username Hongkong Melbourne MD5 Password cisco sanhinoon
Random
ID
01
Response Hash # Hongkong Hash# Is Equal? Sydney Ack/Nack ID 03
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ID
02
PPP Encapsulation And Authentication Process
CONFIGURING PPP
Configuring PPP
Enable PPP
Router(config)#interface serial 0/0 Router(config-if)#encapsulation ppp
To configure compression over PPP, enter the following commands:
Router(config-if)#compress [predictor | stac]
Enter the following to monitor the data dropped on the link, and avoid frame looping:
Router(config-if)#ppp quality percentage
The following commands perform load balancing across multiple links:
Router(config-if)#ppp multilink
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Configuring PPP authentication
Step 1: Define username and password to expect from remote router
Router(config)#username remote password secret Secret must be the same at both ends
Step 2: Enable PPP
Router(config-if) encapsulation ppp
Step 3: Configure authentication
Router(config-if) Ppp authentication { pap|chap|papchap|chap-pap}
Step 4: if IOS 11.1 or later, PAP must be enable on interface
Router(config-if)ppp pap sent-username user password pass
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Configuring PPP and Authentication
Configuring PPP authentication - PAP
Configuring PPP authentication - CHAP
Verifying The Serial PPP Encapsulation Configuration
Houston#sh int serial 1/0:1 Serial1/0:1 is up, line protocol is up Hardware is DSX1 Internet address is 10.10.10.3/24 MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) LCP Open Open: IPCP, CDPCP Last input 00:00:09, output 00:53:17, output hang never Last clearing of "show interface" counters 01:09:05 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 164 Queueing strategy: weighted fair Output queue: 0/1000/64/0 (size/max total/threshold/drops) Conversations 0/1/256 (active/max active/max total) Reserved Conversations 0/0 (allocated/max allocated)
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--More--
Troubleshooting The Serial Encapsulation Configuration
left right
right#debug ppp negotiation
00:02:28: %LINK-3-UPDOWN: Interface Serial0/0, changed state to up 00:02:28: Se0/0 PPP: Using default call direction <omit> right(config-i8: Se0/0 PPP: Phase is AUTHENTICATING, by both [0 sess, 0 load] 00:02:28: Se0/0 CHAP: O CHALLENGE id 14 len 26 from "right" 00:02:28: Se0/0 CHAP: I CHALLENGE id 17 len 25 from "left" 00:02:28: Se0/0 CHAP: O RESPONSE id 17 len 26 from "right" 00:02:28: Se0/0 CHAP: I RESPONSE id 14 len 25 from "left" 00:02:28: Se0/0 CHAP: O SUCCESS id 14 len 4 00:02:28: Se0/0 CHAP: I SUCCESS id 17 len 4
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FRAME RELAY
Content
Frame Relay Technology LMI: Ciscos Implementation of FR LMI Features Frame Relay Sub-Interfaces Configuration of Basic Frame Relay
FRAME RELAY TECHNOLOGY
Introduction
Frame Relay is a Consultative Committee for CCITT and ANSI standard. Defines a process for sending data over a public data network (PDN). A way of sending information over a WAN by dividing data into packets. It operates at the physical and data link layers of the OSI reference model. It relies on upper-layer protocols such as TCP for error correction. Frame Relay uses virtual circuits to make connections.
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Frame Relay terminologies
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Access rate Local management interface (LMI) Committed information rate (CIR) Committed burst (Bc) Committed rate measurement interval (Tc) Excess burst (Be) Forward explicit congestion noti. (FECN) Backward explicit congestion noti.(BECN) Discard eligibility (DE) indicator
Frame Relay technology
Terminologies: Access Rate
The clock speed of the connection (local loop) to the Frame Relay cloud. It is the rate at which data travels into or out of the network
Terminologies: DLCI
Data-link connection identifier. A number that identifies the end point in a Frame Relay network. Significance only to the local network. The Frame Relay switch maps the DLCIs between a pair of routers to create a permanent virtual circuit.
Terminologies: LMI
Local management interface. A signaling standard between the CPE device and the Frame Relay switch Responsible for managing the connection and maintaining status btw the devices.
Terminologies: CIR
Committed information rate. The CIR is the guaranteed rate, that the service provider commits to providing.
Terminologies: Bc
Committed Burst The maximum number of bits that the switch agrees to transfer during a interval.
Terminologies: Tc
Committed Rate Measurement Interval. The time interval shouldnt exceed 125 ms, almost always 125 ms
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Terminologies: Excess burst
The maximum number of uncommitted bits that the switch attempts to transfer beyond the CIR. Dependent on the service offerings available by the vendor, but is typically limited to the port speed of the local access loop.
Terminologies: FECN
Forward explicit congestion notification. When a switch recognizes congestion in the network, it sends a FECN packet to the destination device.
Terminologies: BECN
Backward explicit congestion notification. When a switch recognizes congestion in the network, it sends a BECN packet to the source router, instructing the router to reduce the rate at which it is sending packets.
Frame Relay congestion
Terminologies: DE
Discard eligibility indicator. A set bit that indicates the frame may be discarded in preference to other frames if congestion occurs The DE bit is set on the oversubscribed traffic.
Frame Relay operation
A public FR service is deployed by putting FR switching equipment in the central office of a carrier. Economic benefits are got by from traffic sensitive charging rates and lack of equipment and service maintenance. The lines that connect user devices to the provider can operate at a speed selected from a broad range of data rates. Speeds between 56 kbps and 2 Mbps are typical, although Frame Relay can support lower and higher speeds.
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Frame Relay DLCI
FR standards address PVCs that are configured and managed in a FR network. FR PVCs are identified by DLCIs, that have LOCAL significance. Multiplexing many virtual circuit through a physical medium. FR switches constructs a table mapping DLCI values to outbound ports. The complete path to the destination is established before the first frame is sent.
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Frame Relay DLCI (cont.)
Frame Relay frame format
DLCI: Indicates the DLCI value. Consists of the first 10 bits of the Address field. Congestion Control: The last 3 bits in the address field. These are the FECN, BECN, and discard eligible (DE) bits.
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Frame Relay addressing
DLCI address space is limited to 10 bits. possible 1024 DLCI addresses. The usable portion of these addresses are determined by the LMI type:
The Cisco LMI type supports a range of DLCI addresses from DLCI 16-1007. The ANSI/ITU LMI type supports the range of addresses from DLCI 16-992.
The remaining DLCI addresses are reserved for vendor implementation.
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Frame Relay addressing
LMI: CISCOS IMPLEMENTATION OF FRAME RELAY
LMI functions
To determine the operational status of the various PVCs that the router knows about To transmit keepalive packets to ensure that the PVC stays up and does not shut down due to inactivity To tell the router what PVCs are available Three LMI types can be invoked by the router: ansi, cisco, and q933a
LMI operation
LMI extension functions
In addition to the basic Frame Relay protocol functions for transferring data, the Frame Relay specification includes LMI extensions that make supporting large, complex internetworks easier.
Virtual circuit status messages Multicasting Global addressing Simple flow control
LMI FEATURES
Frame Relay Signaling
Cisco supports three LMI standards:
Cisco ANSI T1.617 Annex D ITU-T Q.933 Annex A
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Frame Relay map
Frame Relay mapping
Network address DLCI The routing table is then used to supply the next-hop protocol address or the DLCI for outgoing traffic. The resolution is done through a data structure called a Frame Relay map. This data structure can be statically configured in the router, or the Inverse ARP feature can be used for automatic setup of the map.
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Frame Relay mapping
Inverse ARP
The Inverse ARP mechanism allows the router to automatically build the Frame Relay map.
1. The router learns the DLCIs that are in use from the switch during the initial LMI exchange. 2. The router then sends an Inverse ARP request to each DLCI for each protocol configured on the interface. 3. The return information from the Inverse ARP is then used to build the Frame Relay map.
Frame Relay Inverse ARP and LMI Signaling
Stages of Inverse ARP and LMI Operation
Frame Relay switching table
The Frame Relay switching table consists of four entries: two for incoming port and DLCI, and two for outgoing port and DLCI. The DLCI could, therefore, be remapped as it passes through each switch; the fact that the port reference can be changed is why the DLCI does not change even though the port reference might change.
Frame Relay switching table
Selecting a Frame Relay Topology
Frame Relay default: nonbroadcast, multiaccess (NBMA)
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FRAME RELAY SUBINTERFACES
What are Frame Relay subinterfaces
Subinterfaces are logical subdivisions of a physical interface. In a subinterface configuration, each PVC can be configured as a point-to-point connection, which allows the subinterface to act as a dedicated line. By using multiple virtual subinterfaces, the overall cost of implementing a Frame Relay network can be reduced.
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FR without subinterface
FR with subinterface
Subinterface
Split horizon routing environments
Split horizon reduces routing loops by not allowing a routing update received on one physical interface to be sent back out that same interface. As a result, if a remote router sends an update to the headquarters router that is connecting multiple PVCs over a single physical interface, the headquarters router cannot advertise that route through the same physical interface to other remote routers.
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Split horizon and reachability problem
Reachability issues: Point-to-point
A single subinterface is used to establish one PVC connection to another physical interface or subinterface on a remote router. Each point-to-point connection is its own subnet. In this environment, broadcasts are not a problem because the routers are pointto-point and act like a leased line.
Reachability issues: Multipoint
A single subinterface is used to establish multiple PVC connections to multiple physical interfaces or subinterfaces on remote routers. All the participating interfaces would be in the same subnet, and each interface would have its own local DLCI. Because the subinterface is acting like a regular Frame Relay network, routing updates are subject to split horizon.
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FRAME RELAY CONFIGURATION
Basic Frame Relay configuration
Basic Frame Relay configuration
A basic Frame Relay configuration assumes that:
you want to configure Frame Relay on one physical interface and that LMI and Inverse ARP are supported by the remote routers.
The LMI notifies the router about the available DLCIs. Inverse ARP is enabled by default, so it does not appear in configuration output.
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Verifying Frame Relay operation
Verifying Frame Relay operation
Configure Frame Relay Switch
Enable Frame Relay Switching
FRSW(conf)# frame-relay switching
Configure interface
FRSW(conf-if)#Encapsulation frame-relay FRSW(conf-if)#frame-relay intf-type dce|dte FRSW(conf-if)#clock rate 56000 FRSW(conf-if)#frame-relay lmi-type cisco|ansi| q933a
FR route (create PVC - Switching Table)
FRSW(conf-if)#frame-relay route <input_dlci> interface <output_interface> <output_dlci>
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Configuration subinterfaces
Configuring Subinterfaces
Point-to-point
Subinterfaces act like leased lines. Each point-to-point subinterface requires its own subnet. Point-to-point is applicable to hub and spoke topologies.
Multipoint
Subinterfaces act like NBMA networks, so they do not resolve the split-horizon issues. Multipoint can save address space because it uses a single subnet. Multipoint is applicable to partial mesh and full mesh topologies.
Multipoint subinterfaces example
Point-to-point subinterfaces example
FRAME RELAY CONFIGURATION EXAMPLES
Configuration: without subinterface
1.0.0.0/8 FR Cloud 9.0.0.0/8 2.0.0.0/8
# interface serial 0 # encapsulation frame-relay LMI type is automatically sensed # ip address 9.0.0.1 255.0.0.0
The encapsulation is Cisco
# router igrp 1 DLCI is learned via LMI status messages # network 1.0.0.0 Inverse ARP # network 9.0.0.0 is enable (by default)
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Configuration: Specified encapsulation
1.0.0.0/8 2.0.0.0/8
DLCI 41
FR Cloud 9.0.0.0/8
DLCI 42
# interface serial 0 # ip address 9.0.0.1 255.0.0.0 # encapsulation frame-relay ietf # frame-relay lmi-type ansi
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Configuration: with subinterface
1.0.0.0/8 2.0.0.0/8
DLCI 41
FR Cloud 9.0.0.0/8
DLCI 42
# interface serial 0 # encapsulation frame-relay # frame-relay lmi-type ansi # interface serial 0.1 point-to-point # frame-relay interface-dlci 41 # ip address 9.0.0.1 255.0.0.0
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Configuration: with subinterface
1.0.0.0/8 2.0.0.0/8
DLCI 41 DLCI 43
FR Cloud 9.0.0.0/8
DLCI 42 DLCI 44
3.0.0.0/8 Intel
# interface serial 0 # encapsulation frame-relay # interface serial 0.1 multipoint # ip address 9.0.0.1 255.0.0.0 # frame-relay interface-dlci 41 # frame-relay interface-dlci 43 ietf
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Configuration: disabled inverse ARP
1.0.0.0/8 2.0.0.0/8
DLCI 41 DLCI 43
FR Cloud 9.0.0.0/8
DLCI 42 DLCI 44
3.0.0.0/8 Intel
# interface serial 0.1 multipoint # ip address 9.0.0.1 255.0.0.0 # frame-relay interface-dlci 41 # frame-relay interface-dlci 43 ietf # frame-relay map ip 9.0.0.2 41 broadcast # frame-relay map ip 9.0.0.3 43 broadcast
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Configuring a Static Frame Relay Map
Configuring Point-to-Point Subinterfaces
Multipoint Subinterfaces Configuration Example
Q&A
