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Table of ContentsDialup Technology: Overviews and Explanations...1 Objectives...1 Modem Operations...2 ISDN Operations...2 Dialer Operations...2 PPP Operations ...2 Modem Operations...2

Cisco − Dialup Technology: Overviews and Explanations

Table of Contents

Dialup Technology: Overviews and Explanations 1

Objectives 1

Modem Operations 2

ISDN Operations 2

Dialer Operations 2

PPP Operations 2

Modem Operations 2

Using the Modem Autoconfigure Command 3

Establishing a Reverse Telnet Session to a Modem 3

Using Rotary Groups 5

Interpreting Show Line Output 5

Gathering Modem Performance Information 9

ISDN Operations 14

ISDN Components 14

16

Interpreting Show ISDN Status Output 19

Dial on Demand Routing: Dialer Interface Operations 22

Triggering a Dial 22

Dialer Maps 30

Dialer Profiles 32

PPP Operations 34

Phases of PPP Negotiation 35

Alternate PPP Methodologies 37

Annotated Example of PPP Negotiation 44

Before Calling the Cisco Systems TAC Team 47

Related Information 48

Cisco − Dialup Technology: Overviews and Explanations

Dialup Technology: Overviews and Explanations

This information from the Internetwork Troubleshooting Guide was first posted on CCO here As a service toour customers, selected chapters have been updated with the most current and accurate information Thecomplete update to the Internetwork Troubleshooting Guide will soon be available in print and online

Using the Modem Autoconfigure Command

Establishing a Reverse Telnet Session to a Modem

Using Rotary Groups

Interpreting Show Line Output

Gathering Modem Performance Information

ISDN Operations

ISDN Components

ISDN Services

Interpreting Show ISDN Status Output

Dial on Demand Routing: Dialer Interface Operations

Annotated Example of PPP Negotiation

Before Calling the Cisco Systems TAC Team

Related Information

Back to main index

Objectives

This chapter introduces and explains some of the technologies used in dialup networks You will find

configuration tips and interpretations of some of the show commands, which are useful for verifying correct

operation of the network Troubleshooting procedures are beyond the scope of this document and can be

found in the document entitled Troubleshooting Dialup.

This chapter focuses on four principal areas:

Using the Modem Autoconfigure Command

If you are using Cisco Internetwork Operating System (Cisco IOS) Release 11.1 or later, you can configureyour Cisco router to communicate with and configure your modem automatically

Use the following procedure to configure a Cisco router to automatically attempt to discover what kind ofmodem is connected to the line, and then to configure the modem:

To discover the type of modem attached to your router, use the modem autoconfigure

discovery line configuration command.

1

When the modem is successfully discovered, configure the modem automatically using the modem

autoconfigure type modem−name line configuration command.

2

If you want to display the list of modems for which the router has entries, use the show

modemcap modem−name If you want to change a modem value that was returned from the show

modemcap command, use the modemcap edit modem−name attribute value line configuration command.

For complete information on the use of these commands, refer to the Cisco IOS Documentation Dial

Solutions Configuration Guide and Dial Solutions Command Reference.

Note: Do not enter &W in the modemcap entry that is used for the autoconfigure This causes the NVRAM

to be rewritten every time a modem autoconfigure is performed and will destroy the modem

Establishing a Reverse Telnet Session to a Modem

For diagnostic purposes, or to initially configure the modem if you are running Cisco IOS Release 11.0 orearlier, you must establish a reverse Telnet session to configure a modem to communicate with a Ciscodevice As long as you lock the data terminal equipment (DTE)–side modem speed, the modem will alwayscommunicate with the access server or router at the desired speed Refer to Table 16–5 for information onlocking the modem speed Be certain that the speed of the Cisco device is configured before issuing

commands to the modem via a reverse Telnet session Again, refer to Table 16–5 for information onconfiguring the speed of the access server or router

To configure the modem for a reverse telnet session, use the line configuration command transport input telnet To set up a rotary group (in this case, on port 1), enter the line configuration command rotary

1 Placing these commands under the line configuration causes IOS to allocate IP listeners for incoming

connections at port ranges starting with the following base numbers:

2000 Telnet protocol

3000 Telnet protocol with rotary

4000 Raw TCP protocol

5000 Raw TCP protocol with rotary

6000 Telnet protocol, binary mode

7000 Telnet protocol, binary mode with rotary

9000 Xremote protocol

10000 XRemote protocol with rotary

To initiate a reverse Telnet session to your modem, perform the following steps:

From your terminal, use the command telnet ip−address 20yy where ip−address is the IP address of

any active, connected interface on the Cisco device, and yy is the line number to which the modem is

connected For example, the following command would connect you to the auxiliary port on a Cisco

2501 router with IP address 192.169.53.52: telnet 192.169.53.52 2001 Generally, a Telnet command

of this kind can be issued from anywhere on the network, if it can ping the IP address in question.

1

Note: On most Cisco routers, port 01 is the auxiliary port On a Cisco access server, the auxiliary

port is the last TTY +1 As an example, the auxiliary port on a 2511 is port 17 (16 TTY ports + 1).

Always use the show line exec command to find the auxiliary port number – particularly on the 2600

and 3600 series, which use non−contiguous port numbers to accommodate varying async module

sizes

If the connection is refused, it could indicate that there is either no listener at the specified address

and port, or that someone is already connected to that port Verify the connection address and port

number Also, make sure the command modem inout or modem DTR−active, as well as transport

input all, appear under the line configuration for the lines being reached.

2

If using the rotary function, make sure the command rotary n also appears in the line configuration

where n is the number of the rotary group To check if someone is already connected, telnet to the

router and use the command show line n Look for an asterisk to indicate the line is in use Make

sure CTS is high and DSR is not Use the command clear line n to disconnect the current session on

port number n If the connection is still refused, the modem might be asserting Carrier Detect (CD)

all the time Disconnect the modem from the line, establish a reverse Telnet session, and then connect

Table 16–1 outlines possible causes of modem−to−router connectivity problem symptoms and describes

solutions to those problems

Table 16−1: No Connectivity Between Modem and Router

Modem control is not enabled on the access

The following example illustrates how to configure a line for both incoming and outgoing calls:

line 5 modem inout

Note: Be certain to use the modem inout command, and not the modem dialin command while the connectivity of the modem is in question The latter command allows the line to accept incoming calls only Outgoing calls will be refused and it will be impossible to establish a Telnet session with the modem in order to configure it If you want to use the modem dialin command, do so only after you are certain the modem is functioning correctly.

Modem could be misconfigured or have a

Using Rotary Groups

For some applications, the modems on a given router need to be shared by a group of users Cisco Dialout

Utility is an example of this type of application Basically, users connect to one port that connects them to an

available modem To add an async line to a rotary group, simply enter rotary n where n is the number of the

rotary group in the configuration for the async line Refer to the example below

The above line configuration would allow users to connect to the rotary group by entering telnet

192.169.53.52 3001 for normal telnet Alternatives include ports 5001 for Raw TCP, 7001 for binary telnet

(which Cisco Dialout Utility uses), and 10001 for Xremote connections

Note: To verify the configuration of the Cisco Dialout Utility, double click on the dialout utility icon at the

bottom right of the screen and press the More> button Next, press the Configure Ports> button Make sure

the port is in the 7000 range, if using rotary groups, and the 6000 range, if the Dialout utility is targeting an

individual modem You should also enable modem logging on the PC This is done by selecting the following

sequence: Start−>Control Panel−> modems−>(choose your Cisco Dialout

modem)−>Properties−>Connection−>Advanced −>Record a log file.

Interpreting Show Line Output

The output from the show line line−number exec command is useful when troubleshooting a

modem−to−access server or router connection Below is the output from the show line command.

as5200−1#show line 1

Tty Typ Tx/Rx A Modem Roty AccO AccI Uses Noise Overruns Int

1 TTY 115200/115200− − − − − 0 0 0/0 −

Line 1, Location: "", Type: ""

Length: 24 lines, Width: 80 columns

Baud rate (TX/RX) is 115200/115200, no parity, 1 stopbits, 8 databits

Status: No Exit Banner

Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol Out

Modem state: Hanging up

modem(slot/port)=1/0, state=IDLE

dsx1(slot/unit/channel)=NONE, status=VDEV_STATUS_UNLOCKED

Group codes: 0

Modem hardware state: CTS noDSR noDTR RTS

Special Chars: Escape Hold Stop Start Disconnect Activation

^^x none − − none

Timeouts: Idle EXEC Idle Session Modem Answer Session Dispatch

00:10:00 never none not set Idle Session Disconnect Warning

Modem type is unknown.

Session limit is not set.

Time since activation: never

Editing is enabled.

History is enabled, history size is 10.

DNS resolution in show commands is enabled

Full user help is disabled

Allowed transports are lat pad telnet rlogin udptn v120 lapb−ta Preferred is l

at pad telnet rlogin udptn v120 lapb−ta.

No output characters are padded

No special data dispatching characters

as5200−1#

When connectivity problems occur, important output appears in the Modem state and the Modem hardwarestate fields

Note: The Modem hardware state field does not appear in the show line output for every platform In certain

cases, the indications for signal states will be shown in the Modem state field instead

Table 16–2 shows typical Modem state and Modem hardware state strings from the output of the show linecommand It also explains the meaning of each state

Table 16−2: Modem and Modem Hardware States in Show Line Output

Idle CTS noDSR DTR RTS These are the proper modem states for connections

between an access server or router and a modem(when there is no incoming call) Output of anyother kind generally indicates a problem

consider the following:

Modem control is not configured on theaccess server or router Configure the

access server or router with the modem inout line configuration command.

♦

The modem configured for DCD isalways high The modem should bereconfigured to have DCD highonly one CD1 This is usually done

with the &C1 modem command,

but check your modemdocumentation for the exact syntaxfor your modem If your softwaredoes not support modem control,you must configure the accessserver line to which the modem is

connected with the no exec line

configuration command Clear the

line with the clear line privileged

exec command, initiate a reverseTelnet session with the modem,and reconfigure the modem so thatDCD is high only on CD End theTelnet session by entering

disconnect and reconfigure the

access server line with the execline configuration command

♦

3

Ready noCTS noDSR DTR RTS The noCTS string appears in the Modem hardware

state field for one of the following four reasons:

The modem is turned off

1

The modem is not properly connected tothe access server Check the cablingconnections from the modem to the accessserver

2

Incorrect cabling (either rolled MDCE, orstraight MDTE, but without the pinsmoved) The recommended cabling

3

configuration is given earlier in this table.The modem is not configured for hardware

flow control Use the no flowcontrol hardware line configuration command to

disable hardware flow control on the accessserver Then enable the hardware flowcontrol on the modem via a reverse Telnetsession (Consult your modem

documentation and see the section

"Establishing a Reverse Telnet Session to aModem" earlier in this chapter.) Re−enablethe hardware flow control on the access

server with the flowcontrol hardware line

configuration command

4

Ready CTS DSR DTR RTS2 The DSR string (instead of the noDSR string)

appears in the Modem hardware state field for one

of the following reasons:

Incorrect cabling (either rolled MDCE, orstraight MDTE, but without the pinsmoved) The recommended cablingconfiguration is given earlier in this table

1

The modem is configured for DCD alwayshigh Reconfigure the modem so that DCD

is only high on CD This is usually done

with the &C1 modem command, but check

your modem documentation for the exactsyntax for your modem Configure theaccess server line to which the modem is

connected with the no exec line

configuration command Clear the line with

the clear line privileged exec command,

initiate a reverse Telnet session with themodem, and reconfigure the modem so thatDCD is high only on CD End the Telnet

session by entering disconnect.

Reconfigure the access server line with theexec line configuration command

2

Ready CTS* DSR* DTR RTS2 If this string appears in the Modem hardware state

field, modem control is probably not enabled on the

access server Use the modem inout line

configuration command to enable modem control

on the line

Additional information on configuring modemcontrol on an access server or router line is

provided earlier in this table.

Gathering Modem Performance Information

This section explains methods for gathering performance data on the MICA digital modems found in theCisco AS5x00 family of access servers The performance data can be used for trend analysis and is useful introubleshooting performance problems that might be encountered When looking at the numbers presentedbelow, bear in mind that perfection is not possible in the real world The possible modem call success rate(CSR) is a function of the quality of the circuits, the client modem userbase, and the set of modulations beingused A typical CSR percentage for V.34 calls is 95% V.90 calls can be expected to connect successfully92% of the time Premature drops are likely to happen 10% of the time

Use the following The commands to gain an overall view of modem behavior on the access server:

Interesting information from the client (after disconnect)−ATI6, ATI11, AT&V, AT&V1, and so on.

Show Modem / Show Modem Summary

The show modem command gives a view of individual modems From these numbers the health of

individual modems can be viewed

router# show modem

Codes:

* − Modem has an active call

C − Call in setup

T − Back−to−Back test in progress

R − Modem is being Reset

p − Download request is pending and modem cannot be used for taking calls

D − Download in progress

B − Modem is marked bad and cannot be used for taking calls

b − Modem is either busied out or shut−down

d − DSP software download is required for achieving K56flex connections

! − Upgrade request is pending

Inc calls Out calls Busied Failed No Succ

Mdm Usage Succ Fail Succ Fail Out Dial Answer Pct

To see the aggregate numbers for all the modems on the router, use the show modem summary command.

router#show modem summary

Incoming calls Outgoing calls Busied Failed No Succ Usage Succ Fail Avail Succ Fail Avail Out Dial Ans Pct 0% 6297 185 64 0 0 0 0 0 0 97%

Table 16−3: show modem Fields

Incoming and Outgoing calls Calls dialing into and out of the modem

Usage − Percentage of the total systemuptime that all the modems are in use

• Succ − Total calls successfully connected

•

Fail − Total calls that did not successfullyconnect.

•

Avail − Total modems available for use inthe system

•

Busied Out Total number of times the modems were taken out

of service with the modem busy command or the modem shutdown command.

Failed Dial Total number of attempts the modems did not hang

up or there was no dial tone

but the calls were not answered by a modem

Succ Pct Successful connection percentage of total available

modems

Show Modem Call−Stats Output

compress retrain lostCarr rmtLink trainup hostDrop wdogTimr inacTout

Mdm # % # % # % # % # % # % # % # % Total 9 41 271 3277 7 2114 0 0

Table 16−4: show modem call−stats Fields

rmtLink This show that error correction was in effect, and the call was hung up by the client

system attached to the remote modem

hostDrop This shows the call was hung up by IOS host system Some common reasons

include: idle timeout, a circuit clear from the telephone company, or a PPP LCPtermreq from the client The best way to determine the reason for the hang up is byusing modem call−record terse or AAA accounting

The other disconnect reasons should add up to less than 10% of the total

Show Modem Connect−Speeds Output

router>show modem connect 33600 0

Mdm 26400 28000 28800 29333 30667 31200 32000 33333 33600 TotCnt Tot 614 0 1053 0 0 1682 0 0 822 6304

router>show modem connect 56000 0

Mdm 48000 49333 50000 50666 52000 53333 54000 54666 56000 TotCnt

Tot 178 308 68 97 86 16 0 0 0 6304

Expect to see a distribution of V.34 speeds There should be a peak at 26.4, if the T1s use channel associated

signaling (CAS) For ISDN (PRI) T1s, the peak should be at 31.2 Also, look for a few K56Flex, V.90

speeds If there are no V.90 connections there may be a network topology problem

Understanding the Modem Call−Record Terse (11.3AA/12.0T) Command

Rather than an exec command, this is a configuration command placed at the system level of the access

server in question When a user disconnects, a message similar to the following displays:

*May 31 18:11:09.558: %CALLRECORD−3−MICA_TERSE_CALL_REC: DS0 slot/contr/chan=2/0/18, slot/port=1/29, call_id=378, userid=cisco, ip=0.0.0.0, calling=5205554099,

called=4085553932, std=V.90, prot=LAP−M, comp=V.42bis both, init−rx/tx b−rate=26400/41333, finl−rx/tx brate=28800/41333, rbs=0, d−pad=6.0 dB, retr=1, sq=4, snr=29, rx/tx chars=93501/94046,

bad=5, rx/tx ec=1612/732, bad=0, time=337, finl−state=Steady, disc(radius)=Lost Carrier/Lost Carrier, disc(modem)=A220 Rx (line to host) data flushing − not OK/EC condition − locally detected/received DISC frame −− normal LAPM termination

Show Modem Operational−Status Command

The exec command show modem operational−status shows the current (or most recent) parameters

pertaining to the modem's connection

The documentation entry for this command is found in the Cisco IOS Release 12.0 Dial Solutions Command

Reference show modem operational−status is only for MICA modems The equivalent command for

Microcom modems is modem at−mode / AT@E1 Use the modem at−mode <slot>/<port> command to

connect to the modem, then issue the AT@E1 command Complete documentation for the modem

at−mode command can be found in the Cisco AS5300 Software Configuration Guide, and documentation for

the AT@E1 command is in the AT Command Set and Register Summary for Microcom Modem Modules

Command Reference.

Use the following steps to determine on which modems a user is coming in on:

Issue the command show user and look for the TTY to which they are connected.

1

Use the command show line and look for the modem slot/port numbers.

2

Gathering Client−Side Performance Data

For trend analysis, it's very important to gather client−side performance data Always try to obtain the

Other information available on the client end includes the PC's modemlog.txt and ppplog.txt You must

specifically configure your PC to generate these files

Analyze the Performance Data

Once you have collected and understood the performance data for your modem system, you need to look atany remaining patterns and components that may need improvement

Problems with Particular Server Modems

Use show modem or show modem call−stats to identify any modems with abnormally high rates of trainup

failure or bad disconnect rates (MICA) If adjacent pairs of modems are having problems, the problem is

likely a hung/dead DSP Use copy flash modem to the affected HMM in order to recover Make sure the

modems are running the latest version of portware

To verify that all modems are correctly configured, use the configuration command modem autoconfigure type <mica/microcom_server> in the line configuration To make sure the modems are being

autoconfigured whenever a call is hung up, use the exec command debug confmodem In order to fix

modems that are badly misconfigured, you may need to establish a reverse Telnet session

Problems with Particular DS0s

DS0 problems are rare, but possible To locate malfunctioning DS0s, use the command show controller t1 call−counters and look for any DS0s with abnormally high TotalCalls and abnormally low TotalDuration.

To target suspected DS0s, you may need to busy out other DS0s with the configuration command isdn service dsl, ds0 busyout under the serial interface for the T1 The output from show controller t1

call−counters looks like this:

TimeSlot Type TotalCalls TotalDuration

1 pri 873 1w6d

2 pri 753 2w2d

3 pri 4444 00:05:22

Obviously, timeslot 3 is the suspect channel in this case

Additional Common Trends

Below are a few of the more common trends seen by the Cisco TAC

Bad circuit paths

If your long distance service isn't functioning properly or at all (but local service is fine):

Be sure that the digital line connects into a digital switch, not a channel bank

♦

Instruct the telephone companies to examine the circuit paths used for long distance.

ISDN is an effort to standardize subscriber services, user/network interfaces, and network and internetworkcapabilities Standardizing subscriber services attempts to ensure a level of international compatibility.Standardizing the user/network interface stimulates development and marketing of these interfaces by

third−party manufacturers Standardizing network and internetwork capabilities helps achieve the goal ofworldwide connectivity by ensuring that ISDN networks easily communicate with one another

ISDN applications include high−speed image applications (such as Group IV facsimile), additional telephonelines in homes to serve the telecommuting industry, high−speed file transfer, and video conferencing Voice,

of course, isl also a popular application for ISDN

The home access market is being divided up among different technologies In areas where newer less

expensive technologies such as DSL and Cable become available the home market is moving away fromISDN Businesses, however, continue to use ISDN in the form of PRI T1/E1s to carry large amounts of data

or to provide v.90 dialin access

ISDN Components

ISDN components include terminals, terminal adapters (TAs), network−termination devices, line−terminationequipment, and exchange−termination equipment ISDN terminals come in two types Specialized ISDNterminals are referred to as terminal equipment type 1 (TE1) Non−ISDN terminals, such as DTE that predatethe ISDN standards, are referred to as terminal equipment type 2 (TE2) TE1s connect to the ISDN networkthrough a four−wire, twisted−pair digital link TE2s connect to the ISDN network through a terminal adapter.The ISDN TA can either be a standalone device or a board inside the TE2 If the TE2 is implemented as astandalone device, it connects to the TA via a standard physical−layer interface Examples include

EIA/TIA−232−C (formerly RS−232−C), V.24, and V.35

Beyond the TE1 and TE2 devices, the next connection point in the ISDN network is the network terminationtype 1 (NT1) or network termination type 2 (NT2) device These are network−termination devices thatconnect the four−wire subscriber wiring to the conventional two−wire local loop In North America, the NT1

is a customer premises equipment (CPE) device In most other parts of the world, the NT1 is part of thenetwork provided by the carrier The NT2 is a more complicated device, typically found in digital private

branch exchanges (PBXs), that performs Layer 2 and 3 protocol functions and concentration services AnNT1/2 device also exists; it is a single device that combines the functions of an NT1 and an NT2.

A number of reference points are specified in ISDN These reference points define logical interfaces betweenfunctional groupings such as TAs and NT1s ISDN reference points include the following:

R—The reference point between non−ISDN equipment and a TA

•

The following is a sample ISDN configuration This sample shows three devices attached to an ISDN switch

at the central office Two of these devices are ISDN−compatible, so they can be attached through an Sreference point to NT2 devices The third device (a standard, non−ISDN telephone) attaches through the Rreference point to a TA Any of these devices could also attach to an NT1/2 device, which would replace boththe NT1 and the NT2 And, although they are not shown, similar user stations are attached to the far rightISDN switch

A Sample ISDN Configuration

The ISDN Basic Rate Interface (BRI) service offers two B channels and one D channel (2B+D) BRI

B−channel service operates at 64 kbps and is meant to carry user data; BRI D−channel service operates at 16kbps and is meant to carry control and signaling information, although it can support user data transmissionunder certain circumstances The D−channel signaling protocol comprises Layers 1 through 3 of the OSIreference model BRI also provides for framing control and other overhead, bringing its total bit rate to 192kbps The BRI physical layer specification is International Telecommunication Union TelecommunicationStandardization Sector (ITU−T; formerly the Consultative Committee for International Telegraph andTelephone [CCITT]) I.430

ISDN Primary Rate Interface (PRI) service offers 23 B channels and one D channel in North America andJapan, yielding a total bit rate of 1.544 Mbps (the PRI D channel runs at 64 kbps) ISDN PRI in Europe,Australia, and other parts of the world provides 30 B plus one 64−kbps D channel and a total interface rate of2.048 Mbps The PRI physical layer specification is ITU−T I.431

Layer 1

The ISDN physical layer (Layer 1) frame formats differ depending on whether the frame is outbound (fromterminal to network) or inbound (from network to terminal) Both physical layer interfaces are shown inFigure 16–1

Figure 16−1: ISDN Physical−Layer Frame Formats

The frames are 48 bits long, of which 36 bits represent data The bits of an ISDN physical layer frame areused as follows:

contention When an NT receives a D bit from the TE, it echoes back the bit in the next E−bit position The

TE expects the next E bit to be the same as its last transmitted D bit

Terminals cannot transmit into the D channel unless they first detect a specific number of ones (indicating

"no signal") corresponding to a pre−established priority If the TE detects a bit in the echo (E) channel that isdifferent from its D bits, it must stop transmitting immediately This simple technique ensures that only oneterminal can transmit its D message at one time After successful D message transmission, the terminal has itspriority reduced by being required to detect more continuous ones before transmitting Terminals cannot raisetheir priority until all other devices on the same line have had an opportunity to send a D message Telephoneconnections have higher priority than all other services, and signaling information has a higher priority thannonsignaling information

Figure 16−2: LAPD Frame Format

The LAPD Flag and Control fields are identical to those of HDLC The LAPD Address field can be either 1

or 2 bytes long If the extended address bit of the first byte is set, the address is 1 byte; if it is not set, theaddress is 2 bytes The first address field byte contains the service access point identifier (SAPI), whichidentifies the portal at which LAPD services are provided to Layer 3 The C/R bit indicates whether the framecontains a command or a response The terminal endpoint identifier (TEI) field identifies either a singleterminal or multiple terminals A TEI of all ones indicates a broadcast

RELEASE, USER INFORMATION, CANCEL, STATUS, and DISCONNECT

These messages are functionally similar to those provided by the X.25 protocol (see Chapter 19,

"Troubleshooting X.25 Connections," for more information) Figure 16−3, from ITU−T I.451, shows thetypical stages of an ISDN circuit−switched call

Figure 16−3 ISDN Circuit−Switched Call Stages

Interpreting Show ISDN Status Output

To find out what the current condition of the ISDN connection is between the router and the telephone

company switch, use the command show isdn status The two kinds of interfaces that are supported by this

command are the BRI and the PRI

3620−2#show isdn status

Global ISDN Switchtype = basic−ni

ISDN BRI0/0 interface

dsl 0, interface ISDN Switchtype = basic−ni

Layer 1 Status:

ACTIVE

Layer 2 Status:

TEI = 88, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED

TEI = 97, Ces = 2, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED

Spid Status:

TEI 88, ces = 1, state = 5(init)

spid1 configured, no LDN, spid1 sent, spid1 valid

Endpoint ID Info: epsf = 0, usid = 0, tid = 1

TEI 97, ces = 2, state = 5(init)

spid2 configured, no LDN, spid2 sent, spid2 valid

Endpoint ID Info: epsf = 0, usid = 1, tid = 1

Layer 3 Status:

0 Active Layer 3 Call(s)

Activated dsl 0 CCBs = 0

The Free Channel Mask: 0x80000003

Table 16−5:− show isdn status for BRI

The BRI interface is shutdown Either check the configuration for

the command shutdown under the BRI interface, or look for an administratively down indication from the show

interface command Use the configuration utility and enter no shutdown under the BRI interface Enter the command clear interface bri at the exec prompt to make sure the BRI interface is

restarted

•

A problem exists with the cabling You will need to replace thecable Make sure you use a straight−through RJ−45 cable To checkthe cable, hold the RJ−45 cable ends side by side If the pins are inthe same order, the cable is straight−through If the order of the pins

is reversed, the cable is rolled Replace the cable

•

The ISDN BRI port of a router might require an NT1 device InISDN, NT1 is a device that provides the interface between thecustomer premises equipment and central office switchingequipment If the router does not have an internal NT1, obtain and

•

connect an NT1 to the BRI port Make sure that the BRI or terminaladapter is attached to the S/T port of the NT1 Refer to the

manufacturer’s documentation to verify correct operation of theexternal NT1

The line might not be functioning Contact the carrier to confirmoperation of the connection and to verify the switch type settings

Contact your service provider to verify the setting configured on the router

To change the SPID settings, use the isdn spidn interface configuration

command Where n is either 1 or 2, depending on the channel in question.

Use the no form of this command to remove the specified SPID.

isdn spidn spid−number [ldn]

no isdn spidn spid−number [ldn]

Syntax Description:

spid−number

The number identifying the service to which you havesubscribed This value is assigned by the ISDN serviceprovider and is usually a 10−digit telephone number withadditional digits

To see the layer 2 negotiations between the switch and the

router, use the privileged exec command debug isdn q921.

The q921 debugs are documented in the Debug Command

Reference Debugs rely heavily on CPU resources, so use

caution when employing them

5200−1# show isdn status

Global ISDN Switchtype = primary−5ess

ISDN Serial0:23 interface

dsl 0, interface ISDN Switchtype = primary−5ess

The Free Channel Mask: 0x807FFFFF

Total Allocated ISDN CCBs = 0

5200−1#

If the show isdn status command does not work or does not show the PRI, try using the show isdn

service command Make sure the pri−group command appears in the configuration under the T1/E1

controller in the configuration If the command is not present, configure the controller with the

The PRI interface is shutdown Either check the configuration

for the command shutdown under the serial0:23 interface or look for an administratively down indication from the show interface command Use the configuration utility and enter no shutdown under the interface in question Enter the command

clear controller T1/E1 n at the exec prompt to make sure the

PRI interface is restarted

•

The line might not be functioning Contact the carrier toconfirm operation of the connection, and to verify the switchtype settings

•

Make sure the router is functioning correctly If there is faulty

or malfunctioning hardware, replace as necessary

To see the layer 2 negotiations between the switch and the router, use

the privileged exec command debug isdn q921 The q921 debugs are

documented in the Debug Command Reference Debugs rely heavily

on CPU resources, so use caution when employing them

Number of calls /

Call Control Blocks in use /

Total Allocated ISDN Call

Control Blocks

These number indicate how many calls are in progress, and thenumber of resources that are allocated to support those calls If thenumber of allocated CCBs is higher than the number of CCBs beingused, consider that there might be a problem in releasing CCBs Makesure there are available CCBs for incoming calls

Dial on Demand Routing: Dialer Interface Operations

Dial on Demand Routing (DDR) is a method of providing WAN connectivity on an economical, as−neededbasis, either as a primary link or as backup for a non−dial serial link

A dialer interface is defined as any router interface capable of placing or receiving a call This generic term should be distinguished from the term Dialer interface (with a capital ‘D’), which refers to a logical interface

configured to control one or more physical interfaces of a router and which is seen in a router configuration

as interface Dialer X From this point forward, unless otherwise stated, we will be using the term ‘dialer’ inits generic sense

Dialer interface configuration comes in two flavors: dialer map−based (sometimes referred to as ‘LegacyDDR’), and dialer profiles Which method you use depends on the circumstances under which you need dialconnectivity Dialer map−based DDR was first introduced in IOS version 9.0, dialer profiles in IOS version11.2

Triggering a Dial

At its heart, DDR is just an extension of routing wherein interesting packets are routed to a dialer interface,

triggering a dial attempt The following sections explain the concepts involved in defining interesting trafficand explain the routing used for DDR connections

Interesting packets

Interesting is the term used to describe packets or traffic that will either trigger a dial attempt or, if a dial link

is already active, will reset the idle timer on the dialer interface For a packet to be considered interesting:

the packet must meet the "permit" criteria defined by an access−list,

•

the access−list must be referenced by the dialer−list or the packet must be of a protocol which is

universally permitted by the dialer−list, and

•

the dialer list must be associated with a dialer interface by use of a dialer−group

•

Packets are never automatically considered to be interesting (by default) Interesting packet definitions must

be explicitly declared in a router or access server configuration

Dialer Group

In the configuration of each dialer interface on the router or access server, there must be a

dialer−group command If the dialer−group command is not present, there is no logical link between the

interesting packet definitions and the interface The command syntax:

dialer−group [group number]

The group number is the number of the dialer access group to which the specific interface belongs This

access group is defined with the dialer−list command Acceptable values are nonzero, positive integers

between 1 and 10

An interface can be associated with a single dialer access group only; multiple dialer−group assignment is not

allowed A second dialer access group assignment will override the first A dialer access group is defined

with the dialer−group command The dialer−list command associates an access list with a dialer access

group

Packets that match the specified dialer group trigger a connection request

The destination address of the packet is evaluated against the access list specified in the associated

dialer−list command If it passes, either a call is initiated (if no connection has already been established) or

the idle timer is reset (if a call is currently connected)

Dialer List

The dialer−list global configuration command is used to define a DDR dialer list to control dialing by

protocol, or by a combination of protocol and access list Interesting packets are those which match the

protocol−level permit or which are permitted by the list in the dialer−list command:

dialer−list dialer−group protocol protocol−name {permit | deny | list access−list−number | access−group}

dialer−group is the number of a dialer access group identified in any dialer−group interface configuration

command

protocol−name is one of the following protocol keywords: appletalk, bridge, clns, clns_es, clns_is, decnet,

decnet_router−L1, decnet_router−L2, decnet_node, ip, ipx, vines, or xns

permit permits access to an entire protocol.

deny denies access to an entire protocol.