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640-505 BCRAN (Building Cisco Remote Access Networks)

This study guide is developed to provide you with an overview of the Cisco 505 BCRAN subject. You are suggested to use this study guide to give yourself a “bird eye view” of the exam. For further study and more in-depth coverage of the topics, the following books are recommended:

Cisco CCNP Preparation Library, Second Edition (Cisco Career Certifications) -- Diane Teare, et al; Hardcover

CCNP Remote Access Study Guide Exam 640-505 (With CD-ROM) -- Todd Lammle, et al; Hardcover

CCNP Remote Access Exam Cram (Exam 640-505) -- Craig Dennis, Eric Quinn; Paperback

CCNP Building CISCO Remote Access Networks Study Guide (Exam 640-505) -- Syngress Media; Hardcover

Exam Objectives

According to Cisco, the Cisco Remote Access exam includes topics on wide area network concepts, configuration of an asynchronous interface on a Cisco router, implementing Point-to-Point Protocol and various authentication schemes, Dial-on-Demand Routing, and leased lines.

Readings

Similar to most of the Cisco exam, you must be familiar with concepts of TCP/IP and the OSI model.

For a good tutorial on TCP/IP, you may visit http://www.3com.com/nsc/501302.html

In addition, you may learn more about the OSI model at http://www.rad.com/networks/1994/osi/intro.htm

This exam has a lot of WAN stuff. You should have solid knowledge on ISDN, X.25 and Frame Relay:

For information on ISDN: http://www.ralphb.net/ISDN/

For tutorial on Frame Relay: http://www.uswest.com/products/data/frame/tutorial/

For tutorial on X.25: http://www.rad.com/networks/1996/x25/x25.htm

Tutorials on PPP: http://cio.cisco.com/warp/public/779/smbiz/service/knowledge/wan/ppp_auth.htm

Commands for setting up X.25 and LAPB: http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/wan_c/wcdx25.htm

Configuring Frame Relay: http://www.cisco.com/warp/public/125/13.html

Configuring ISDN DDR http://www.cisco.com/warp/public/793/access_dial/ddr_dialer_profile.html

Configuring ISDN line http://www.cisco.com/univercd/cc/td/doc/product/access/acs_mod/1600/1600icg/isdn.htm

Apart from WAN connectivity, you must also be familiar with the various remote access authentication and security technologies:

Tutorials on PAP and CHAP: http://www.cisco.com/warp/public/474/9.html

Advanced traffic shaping http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/ciscoasu/class/qpm1_1/using_qo/c1plan.htm#xtocid321011

Outbound traffic queuing http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/ciscoasu/class/qpm1_1/using_qo/c1plan.htm#xtocid321016

RSVP http://www.cisco.com/univercd/cc/td/doc/product/rtrmgmt/ciscoasu/class/qpm1_1/using_qo/c1plan.htm#xtocid321028

Tutorial on RADIUS: http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/secur_c/scprt2/scradius.htm

Tutorial on TACACS: http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/secur_c/scprt2/sctcacs.htm

Introduction to VPN: http://www.cisco.com/warp/public/779/largeent/learn/technologies/VPNs.html

NAT Configuration http://www.cisco.com/warp/public/701/60.html

===========================================================

Do NOT use this study guide as your sole study resource. Successful completion of the 505 exam requires both practical experience as well as lots and lots of reading.

On the actual exam you will encounter questions on IOS commands as well as many terms. For the commands, Cisco’s original documentation has very detailed coverage.

Here you go….

===========================================================

WAN Connections

3 types of connection:

Dedicated connection via Synchronous serial

Continuously available links
Protocols include PPP, HDLC, SLIP

Circuit-switched connection via Asynchronous serial or ISDN

Requires call setup
Requires call teardown
Connections are made based on needs
Protocols include PPP, SLIP

Packet-switched connection via Synchronous serial

Establish VCs
Share bandwidth
Lower cost than leased line
Protocols include X.25, Frame Relay, ATM

Considerations when choosing a WAN connection type

Amount of data transfer
Availability
Bandwidth
Cost
Management
QoS
Security

Comparison between the alternatives

Dedicated Lease Line

Circuit-Switching

Packet-switching

24 x 7 connection
Very stable
Point-to-point fixed path
Maximum control
Expensive

Uses the phone company networks
Mostly on as needed basis
Lower cost (charge based on usage)

Shared bandwidth
More efficient than circuit switching and less costly than leased line
Can go for 24 x 7 connection
Non-fixed path
Less control than lease line

Site Considerations

Central Site

Must provide access to multiple users from different sites
Must control the costs

Branch Site

Must be able to connect to the central site

Telecommuter Site

Must be able to access company information on demand
Request may be made from various remote locations

You use the Cisco Product Selection Tools to choose the appropriate products for the connection types.

Cisco 700 series router is for:

Telecommuter
Small office
Home office

Functions include:

Networking
Routing
WAN Connectivity
ISDN
Telephony

Router Access Modes

Character mode‘s 4 line types:

AUX stands for Auxiliary port

Uses RJ45

CON stands for Console port

Uses RJ45

TTY refers to the Asynchronous port
VTY refers to the Virtual terminal

Packet mode’s types:

Async or Group-async
BRI or PRI
Serial
Dialer profiles
Dialer rotaries

Modem

Classified as Data communications equipment DCE
Converts digital signals to analog signals
Signaling functions:

TxD - Transmit data
RxD - Receive data
GRD - Grounding

Hardware flow control:

RTS - Request To Send
CTS - Clear To Send

Modem control:

DTR - Data Terminal Ready
CD - Carrier Detect
DSR - Data Set Ready

Modem Modulation ITU Standards:

V.22 : 1200 bps
V.22bis : 2400 bps
V.32 : 9600 bps
V.32bis : 14.4 kbps
V.34 : 28.8 kbps
V.34 annex 1201H : 33.6 kbps
V.90 : 56 kbps

Error detection & correction with Microcom Networking Protocol MNP

MNP 2–4 in public domain
MNP 10 for cellular

Error detection & correction with CCITT V.42

LAP-M
MNP 4

Data compression

MNP - 5: 2:1 compression ratio
V.42bis - 4:1 compression ratio

Modem autoconfiguration

Can configure the modems without the need to use modem configuration commands
Can auto-discover the modems
Can reconfigure the modems each time the AT commands are sent to match the current line settings

PPP

Multiple protocol encapsulations are done with NCP
Link setup and control are done with LCP
Multiple protocols supported
PPP PAP is a type of authentication that uses clear text
Keep in mind that clear text transfer is always insecure
PPP CHAP is a type of authentication much more secure than PAP, as traffic is encrypted
To enable CHAP, you need to enable PPP encapsulation for the router interface, then enable chap with ppp and finally set the usernames and passwords
Provide callback when the callback timer is stopped
Also provide callback service when the PPP NCP negotiation is successful

Multilink PPP

Load balanced PPP
Controlled by adding a sequencing header in the PPP frame
Can work with:
Asynchronous serial interface
Synchronous serial interface
BRI and PRI interfaces
Can work on a dialer rotary group

LAPB

A serial encapsulation method for private serial line
Work at the data link layer
Enable orderly reliable data exchange between DTE and DCE
Need to use one of the X.25 packet-level encapsulations when this is attaching to an X.25 network
2 types of hosts:

Data terminal equipment DTE
Data circuit-terminating equipment DCE

Router using LAPB can act as a DTE or DCE at the protocol level
Provide greater throughput than High-Level Data Link Control encapsulation in congested environment
Router resends the missing frame but not waiting for the higher layers to recover
Uses priority and custom queueing to improve the responsiveness of a link to a given type of traffic
Priority queueing assigns packets to one of the 4 output queues: high, medium, normal, or low priority
Custom queueing assigns packets to one of the 10 output queues and controls the % of the available bandwidth for the queue

X.25

Work at layer 3
Router can act as a DTE or DCE protocol device
Default serial encapsulation is HDLC
Can use DDN, BFE encapsulation or IETF standard encapsulation
An X.25 encapsulation method must be explicitly configured
Can maintain multiple connections over one physical link between DTE and DCE
Can maintain max 4095 VCs
X.25 VC can be identified by its logical channel identifier LCI or virtual circuit number VCN
VC numbers are broken into 4 ranges:

Permanent virtual circuits
Incoming-only circuits

For SVC
Only DCE can initiate call

Two-way circuits for SVC

DCE and DTE can initiate call

Outgoing-only circuits for SVC

Only DTE can initiate call

DTE and DCE devices must have identical VC ranges and identical modulos

Modulo

LAPB modulo128

Also known as extended mode
Can be used to achieve higher throughput across the DTE or DCE interface

X.25 PLP modulo 128

For achieving higher end-to-end throughput for VCs
Allows more data packets to be in transit across the X.25 network

ISDN

Stands for Integrated Services Digital Network
Refers to a specific set of digital services provided through a standard interface
Provides end-to-end digital connectivity
Voice and data are carried by bearer B channels
Control is handled by D channel
Out-of-Band signal does not disturb established connections
Very fast call setup time
Basic Rate Interface BRI = 2 64 kbps B channels + 1 16 kbps D channel
Primary Rate Interface PRI = 23 B channels + 1 64 kbps D channel
In Europe, PRI = 30 B channels + 1 64 kbps D channel
H channels can aggregate B channels
ISDN devices include ISDN Terminal Adapters and ISDN Routers
In the U.S, phone company provides BRI customers with U interface
U interface is a two-wire single pair interface
Only a single device can be connected to a U interface
The device connected to a U interface is called a Network Termination 1 NT-1
NT-1 converts the 2-wire U interface into the 4-wire S/T interface
Devices designed for ISDN are designated as Terminal Equipment 1 TE1
POTS telephone interface is known as the R interface
Analog phones, FAX and modems are designated as Terminal Equipment 2 TE2
We use Terminal Adapters TA to connect a TE2 to an ISDN S/T bus
ISDN is a common choice for DDR

DDR

Short for Dial on Demand Routing
Dialer rotary group allows a single logical interface configuration for a number of physical interfaces
Dialer profiles allow the separation of logical and physical interface configuration
For DDR to work, we must define the interesting traffic and assign the definition to the ISDN interface

Dialer Profile

You can create different configurations for the ISDN B channels of a PRI connection
Allows BRIs to join multiple dialer pools
You can set different DDR parameters for each B channel
You can bridge multiple destinations
Remote routers or users can have independent customized dialer profiles
Components include:

Dialer interfaces
Dialer pool
Physical interfaces
Dialer map-class (optional)

Dial Backup

When a line is in standby mode, the line will be activated when the primary line fails or when it reaches a certain utilization level
Dialer interfaces allow us to have the backup without deactivating the physical interface.
If you are running OSPF, IGRP and EIGRP, you can load share between the primary and backup links

BOD

Short for Bandwidth on demand
Provides dynamic bandwidth allocation and sharing
Triggered by outgoing traffic levels

Frame Relay

Works at the data link layer
Handles multiple virtual circuits
Uses HDLC encapsulation
More efficient than X.25
PVCs are permanent
SVCs are temporary
Topology supported:

Star
Full-mesh
Partial-mesh

Subinterface types supported:

Point-to-point
Multipoint

DLCIs

Used to identify logical virtual circuit between the CPE and the Frame Relay Switch
Short for data-link connection identifier
Specifies a PVC or SVC in a Frame Relay network
In Frame Relay specification DLCIs are locally significant
In LMI DLCIs are globally significant

LMI signaling

Short for Local Management Interface
Enhancements to the basic Frame Relay specification
Keepalive mechanism -verify data flow
Multicast mechanism - provide network server with local DLCI
Status mechanism - provide outgoing status on known DLCIs

Traffic Shaping

Limits the rate of data transmission
Limitation based on:

Specific configured rate
Derived rate based on the level of congestion

Methods:

Rate enforcement on per-VC basis
Generalized BECN support on per-VC basis
Priority/custom/weighted fair queuing

QoS related services

Smart Queuing Techniques:

Assigns different amounts of queue space to various packet service queues in round-robin fashion
No one user can monopolize all the bandwidth

Weighted Random Early Detection:

Combines IP precedence and Random Early Detection capabilities
Provide differentiated performance characteristics for different service classes

Generic Traffic Shaping:

Uses queuing on ATM, Frame Relay or other network
Limit surges that cause congestion

Committed Access Rate:

Allocate bandwidth commitments and limitations to traffic sources and destinations

Link Fragmentation and Interleaving:

Designed for packetized voice running on slow links

RTP Header Compression:

Designed for multimedia traffic

Fair Queuing Operation

Messages are sorted into conversations
Conversations are assigned a channel
Queues are sorted by the order of the last bit crossing the channel
Messages are transmitted in “fair order”

Custom Queuing

Handles the queues in a round-robin fashion

PBR

Short for Policy-based routing
Introduced in Cisco IOS Release 11.0
Provides a mechanism to mark packets - certain kinds of traffic receive differentiated, preferential service
Classify traffic using ACLs
Distributes traffic among multiple paths
Implement routing based on:

Application
End system identity
Protocol
Packet sizes

Specified on the interface that receives the packets
Never specified on the interface from which the packets are sent
Source-Based Transit Provider Selection – for routing traffic from different sets of users through different Internet connections across the policy routers

Compression

Processor utilization proportional to the traffic amount being compressed
Cisco hardware compression adapters support PPP stacker compression and frame relay FRF.9 stacker compression – speed up compression processing
With VIP2 slot, compression works can be offloaded to the VIP2's processor
IOS supports the following compression:

Link compression for per-interface compression

Protocol independent
Uses STAC or Predictor

Payload compression for per-virtual circuit compression

Compresses only the data portion

TCP header compression

Compresses the TCP/IP header only

Microsoft Point-to-Point Compression

CiscoSecure

Provides AAA services
Authentication = determining users identity
Authorization = determining what the users can do
Accounting = billing based on usage
CiscoSecure ACS server includes:

AAA server
Netscape Fastrack server
RDBMS
GUI client

We use Cisco Secure Policy Manager to define security policies for multiple Cisco firewalls and VPN gateways

RADIUS

Short for remote access dial in user services
Runs in a distributed client server setup
For securing your network against possible unauthorized access
Authentication + Authorization
Possible RADIUS server responses

ACCEPT
REJECT
CHALLENGE
CHANGE PASSWORD

TACACS+

Next generation of TACACS
Runs with AAA
Separates authentication, authorization, and accounting

NAT

Short for Network Address Translation
Translation is done by the mapping between inside local addresses and global addresses
Used when:

You do not have enough true IP addresses for use
You want to hide your internal IP addressing

Components:

Inside local IP addresses
Inside global IP addresses for representing the inside local IP addresses
Outside global IP address
Outside local IP address

Type of mappings:

Simple translation for mapping one IP address to another.
Extended translation entry for mapping address and ports. You can have different inside local addresses mapped to the same inside global address. By doing this you are actually using port numbers as the real identification.

Inside-to-outside translation occurs after routing
Outside-to-inside translation occurs before routing
TCP load distribution - dynamic form of round-robin translation based on destination
Number of session that can be handled is bounded by available Router RAM, as each NAT translation session will use about 160 bytes of RAM
PAT:

Can enables hosts on your private networks to communicate over the public networks
Can conserves IP addresses
Porthandler Operation - only packets destined for the server are allowed to go through. This is on a by-type basis

This study guide is developed in Year 2001 by Yu Chak Tin Michael.

His personal web site is located at: http://michaelyu.freeservers.com. You may also email him at: ycthk@i-cable.com