Debugging ISDN Layer

Message

Explanation

Possible Solution

ID-Denied

The ISDN switch cannot assign the requested Terminal Endpoint Identifier (TEI). If this message has AI=127, then the ISDN switch has no TEIs available.

It is usually followed by another IDREQ from the router.

Reset the BRI interface using clear interface bri number or shut/no shut on the interface.

If AI=127, then contact the telco/provider.

IDREM

The ISDN switch has removed the TEI (ID) from the connection. The routermust discard all exiting communication using that TEI.

Check to see if a new TEI is assigned at a later time. If not, contact the telco.

DISC

The side sending the DISConnect message has terminated Layer 3 operation on the link. It may be UAcknowledged by the other side. The router should then send a SABME message reestablishing the link.

If the disconnect message originatedfrom the router, reset the interface using clear interface bri number or shut/no shut on the interface. If the DISC message originated from the ISDN switch, contact the telco. If the router does not initiate a SABME, reset the interface first.

DM

Acknowledged Disconnect Mode. The device sending this message does not wish to enter the Multiple Frame Established state. The router will remain in Layer 2 state TEI_ASSIGNED. SABMEs are retransmitted until the other side responds with a UA instead of a DM.

If the DM is generated bythe router, reset the interface using clear interface bri number or shut/no shut on the interface.

If the DM message originatedfrom the ISDN switch, contact the telco.

FRMR

A Frame Reject Response (from the ISDN switch) indicates an error that cannot be recovered by retransmission. The router will initiate a Layer 2 reset and transmit a SABME for transition to state Multiple Frame Established.

If the router does not initiate a SABME, reset the interface using clear interface bri number or shut/no shut on the interface.

© 2001, Cisco Systs

ms. Inc. All rights reserved.

Cisco CCIE Prep v1.0—Module 3-85

Use the debug isdn q921 EXEC command to display data link layer (Layer 2) access procedures that are taking place at the router on the D channel (LAPD) of its Integrated Services Digital Network (ISDN) interface.

The ISDN data link layer interface provided by the router conforms to the user interface specification defined by ITU-T recommendation Q.921. The debug isdn q921 command output is limited to commands and responses exchanged during peer-to-peer communication carried over the D channel. This debug information does not include data transmitted over the B channels that are also part of the router's ISDN interface. The peers (Data-Link layer entities and layer management entities on the routers) communicate with each other via an ISDN switch over the D channel.

Turn on debug isdn q921 to see the messages that are transmitted from the router to the telco ISDN switch. You should then use the clear interface bri number to reset the BRI interface. This forces the router to renegotiate Layer 2 information with the telco ISDN switch.

Layer 2 problems cannot often be rectified at the customer site. However, Layer 2 debugs (or the interpretation of the debugs) can be provided to the telco for their reference. The debug isdn q921 command output provides details on the Layer 2 transaction occurring between the ISDN switch and the router.

Pay attention to the direction of the messages. The debugs indicate whether the messages were generated by the router (indicated by TX ->) or if they were received by the router (indicated by

RX <--). In the example below, the first message (IDREQ) is sent by the router, while the second (IDASSN) is from the ISDN switch:

*Mar 1 00:03:46.976: ISDN BRO: TX -> IDREQ RI = 29609 AI = 127

*Mar 1 00:03:47.000: ISDN BRO: RX <- IDASSN RI = 29609 AI = 96

You can identify the source of the problem by following the direction of a particular message and the response. For example, if the telco ISDN switch unexpectedly sends a Layer 2 disconnect, the router will reset Layer 2 as well. This indicates that the problem lies with the telco ISDN switch.

Identifying Messages Indicating Layer 2 Problems

The router and the ISDN switch transmit and receive many Layer 2 messages. Most of the messages are normal and are used to verify normal operation. However, some messages can indicate Layer 2 problems. Though occasional resets may not affect service, if you observe extended periods of Layer 2 instability, you should take a closer look at the circuit.

The table shown on the previous page lists the debug isdn q921 Layer 2 messages that indicate problems.

Here is an example of a received DISC message:

Jan

30

10

50

18

523:

ISDN BR1/0: RX <- RRf sapi = 0 tei = 71 NR = 0

Jan

30

10

50

23

379:

ISDN BR1/0: RX <- DISCp sapi = 0 tei = 71

Jan

30

10

50

23

379:

%ISDN-6-Layer2DOWN: Layer 2 for Interface BR1/0,TEI 71

changed to down

Jan 30 10:50:23.383: ISDN BR1/0: TX -> UAf sapi = 0 tei = 71

changed to down

Jan 30 10:50:23.383: ISDN BR1/0: TX -> UAf sapi = 0 tei = 71

sco.com

R4# debug isdn q931 TX -> SETUP pd = 8 callref = 0x04 Bearer Capability i = 0x8890 Channel ID i = 0x83

Called Party Number i = 0x80, '415555121202' RX <- CALL_PR0C pd = 8 callref = 0x84

Channel ID i = 0x89 RX <- CONNECT pd = 8 callref = 0x84 TX -> C0NNECT_ACK pd = 8 callref = 0x04 Success rate is 0 percent (0/5)

Sample Debug ISDN Q931 OutputCall Setup Procedure for an Outgoing Call sco.com

R4# debug isdn q931 TX -> SETUP pd = 8 callref = 0x04 Bearer Capability i = 0x8890 Channel ID i = 0x83

Called Party Number i = 0x80, '415555121202' RX <- CALL_PR0C pd = 8 callref = 0x84

Channel ID i = 0x89 RX <- CONNECT pd = 8 callref = 0x84 TX -> C0NNECT_ACK pd = 8 callref = 0x04 Success rate is 0 percent (0/5)

Sample Debug ISDN Q931 OutputCall Setup Procedure for an Outgoing Call

Sample Debug ISDN Q931 Output-Call Setup Procedure for an Incoming Call

R4# debug isdn q931

Bearer Capability i = 0x8890

Channel ID i = 0x89

Calling Party Number i = 0x0083, '81012345678902'

TX -> CONNECT pd = 8 callref = 0x86 RX <- C0NNECT_ACK pd = 8 callref = 0x06

© 2001, Cisco Systems, Inc. All rights reserved.

Cisco CCIE Prep v1,0—Moc

5-86

Use the debug isdn q931 EXEC command to display information about call setup and teardown of ISDN network connections (Layer 3) between the local router (user side) and the network.

The ISDN network layer interface, provided by the router, conforms to the user interface specification defined by ITU-T recommendation Q.931. It is supplemented by other specifications such as switch type VN4. The router tracks only activities that occur on the user side, not the network side, of the network connection. The information displayed with the debug isdn q931 command is limited to commands and responses exchanged during peer-to-peer communication carried over the D channel. This debug information does not include data transmitted over the B channels, which are also part of the router's ISDN interface. The peers (network layers) communicate with each other via an ISDN switch over the D channel.

A router can be the calling or called party of the ISDN Q.931 network connection call setup and teardown procedures. If the router is the calling party, the command displays information about an outgoing call. If the router is the called party, the command displays information about an incoming call.

You can use the debug isdn q931 command with the debug isdn events and the debug isdn q921 commands at the same time. The displays will be intermingled. Use the service timestamps debug datetime msec global configuration command to include the time with each message.

R4# debug

16:24:47

16:24:47

16:24:47

16:24:47

16:24:47

16:24:47

16:24:47

16:24:49

16:24:49

16:24:50

16:24:51

dialer

%LINK-3-UPDOWN: Interface BRIO/O:l, changed state to down BRO/Osl DDR: disconnecting call

%LINK-3-UPDOWN: Interface BRIO/O:2, changed state to down BRO/O:2 DDR: disconnecting call

BRO/O DDR: Dialing cause ip (s=l72.l6.l4.l, d=224.O.O.5) BRO/O DDR: Attempting to dial 384O2O

%LINK-3-UPDOWN: Interface BRIO/O, changed state to up %ISDN-6-LAYER2UP: Layer 2 for Interface BRO/O, TEI 64 changed to up %LINK-3-UPDOWN: Interface BRIO/O:l, changed state to up BRO/O:l DDR: dialer protocol up

%LINEPROTO-5-UPDOWN: Line protocol on Interface BRIO/O :l, changed state to %ISDN-6-CONNECT: Interface BRIO/O:l is now connected to 384O2O Rl sc-0 .com

R4# debug

16:24:47

16:24:47

16:24:47

16:24:47

16:24:47

16:24:47

16:24:47

16:24:49

16:24:49

16:24:50

16:24:51

dialer

%LINK-3-UPDOWN: Interface BRIO/O:l, changed state to down BRO/Osl DDR: disconnecting call

%LINK-3-UPDOWN: Interface BRIO/O:2, changed state to down BRO/O:2 DDR: disconnecting call

BRO/O DDR: Dialing cause ip (s=l72.l6.l4.l, d=224.O.O.5) BRO/O DDR: Attempting to dial 384O2O

%LINK-3-UPDOWN: Interface BRIO/O, changed state to up %ISDN-6-LAYER2UP: Layer 2 for Interface BRO/O, TEI 64 changed to up %LINK-3-UPDOWN: Interface BRIO/O:l, changed state to up BRO/O:l DDR: dialer protocol up

%LINEPROTO-5-UPDOWN: Line protocol on Interface BRIO/O :l, changed state to %ISDN-6-CONNECT: Interface BRIO/O:l is now connected to 384O2O Rl

Debug Dialer Monitors

• Call Initialization

• Interesting Traffic

Debug Dialer Monitors

• Call Initialization

• Interesting Traffic

Cisco CCIE Prep v1.0—Module 3-87

rights reserv

Use the debug dialer command to verify that the router is initiating a call properly and to verify that the DDR configuration is correct.

You can also use the debug dialer command to verify that the router is receiving interesting traffic and has the appropriate dialer map or dialer string to initiate the call.

Most messages are self-explanatory; however, messages that may need some explanation are described in the table below.

Table 3-4: Interpreting debug dialer Output

General debug dialer events Message Descriptions

Description

DialerO: Already xxx call(s) in progress on DialerO, dialing not allowed

This message occurs when the number of calls in progress (xxx) exceeds the maximum number of calls set on the interface.

DialerO: No free dialer - starting fast idle timer

This message occurs when all the lines in the interface or rotary group are busy and a packet is waiting to be sent to the destination.

BRIO: rotary group to xxx overloaded (yyy)

This message occurs when the number dialer (xxx) exceeds the load set on the interface (yyy).

BRIO: authenticated host xxx with no matching dialer profile

This message occurs when no dialer profile matches xxx, the remote host's CHAP name or remote name.

BRIO: Can't place call, verify configuration

This message occurs when you have not set the dialer string or dialer pool on an interface.

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  • swen
    What messages we will see for debugg isdn q921 in cisco?
    6 months ago

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