Scenario 2: Dial-Out Problems


The very first thing the router should be able to do is make outgoing calls and accept incoming ones. A variety of complexities are related to dial functions, but keep in mind that, regardless of first layer functions, a call requires all three layers to be set up correctly.

Begin dial issue troubleshooting with the show isdn active command. This command shows the active outgoing calls, called party number, and called remote site name, as displayed in Example 13-5.

Example 13-5. show isdn active Output
 804-isdn#show isdn active                                 ISDN ACTIVE CALLS -------------------------------------------------------------------------------- Call   Calling Called       Remote    Seconds Seconds   Seconds   Charges Type   Number  Number       Name      Used    Left      Idle      Units/Currency -------------------------------------------------------------------------------- Out             +8007735555 gateway   64       -         -         0 Out             +8007735555 gatewaay  31       -         -         0 804-isdn# 

If you don't see the router calling out, you should see if the remote user router has ever made calls out. For this and other information, use IOS command show dialer. Example 13-6 shows the output for this command.

Example 13-6. Output for the show dialer Command
 804-isdn#show dialer BRI0 - dialer type = ISDN Rotary group 1, priority = 0 0 incoming call(s) have been screened. 0 incoming call(s) rejected for callback. BRI0:1 - dialer type = ISDN Idle timer (60 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re-enable (15 secs) Dialer state is multilink member Connected to 18007735555 (access-gw1) BRI0:2 - dialer type = ISDN Idle timer (60 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re-enable (15 secs) Dialer state is idle Di1 - dialer type = IN-BAND SYNC NO-PARITY Load threshold for dialing additional calls is 20 Idle timer (60 secs), Fast idle timer (20 secs) Wait for carrier (30 secs), Re-enable (15 secs) Number of active calls = 1 Dial String      Successes   Failures    Last DNIS   Last status 18007735555#             1        164    03:57:41           failed 18007735555             95        165    00:11:05       successful 

A detailed description of the command line's output is shown in Table 13-3.

Table 13-3. Description of the Output from the show dialer Command

Output

Description

BRI0 - dialer type = ISDN

Rotary group 1, priority = 0

0 incoming call(s) have been screened.

0 incoming call(s) rejected for callback.

D channel.

Dialer 1 is a member of rotary group 1.

There is no setting in the config for call screening.

There is no setting in the configuration for callback.

BRI0:1 - dialer type = ISDN

Dialer state is multilink member

BRI1 and BRI2 are defined as a member of MP group.

Di1 - dialer type = IN-BAND SYNC NO-PARITY

Load threshold for dialing additional calls is 20

Dialer 1 performs in-band dialing. The threshold for BRI2 is set to 20/255 x bandwidth, which for ISDN is 128 kbps.

Idle timer (60 secs)

The dialer is idle before disconnecting the call.

The command line is 804-isdn(config-if)#dialer idle-timeout [0-2147483].

Fast idle timer (20 secs)

The fast-idle timer is activated if there is another packet waiting for a different next hop address. The default is 20 seconds and the command is pnedeltc-isdn(config-if)#dialer fast-idle [1-2147483].

Wait for carrier (30 secs)

Wait for carrier before making a call.

pnedeltc-isdn(config-if)#dialer wait-for-carrier-time [1-2147483]

Re-enable (15 secs)

Wait interval before redialing.

804-isdn(config-if)#dialer redial interval [5-2147483]

Number of active calls = 2

Number of active calls at the moment.

Dial String   Successes  Failures  Last DNIS  Last status
18007735048#         1     164    03:57:41     failed
18007735048         95     165    00:11:05   successful

Dialer statistics for every dialer map:

String to dial (# indicates secondary)

Number of successful calls

Number of failures

Time from the last call

Whether the last call was a failure or success


This is not the only command that can provide information on dial-out issues. The following commands are also recommended:

 804-isdn#debug dialer 804-isdn#debug dialer [events | packets] 804-isdn#show running-config  interface dialer 1 

The last command enables you to check the configuration of the dialer 1.

The result of the previous commands usually will allow you to define the problem. The Table 13-4 provides a brief overview of well-known dial issues and their possible resolution.

Table 13-4. Dial Problems, Reasons, and Solutions

Problem

Reason/Solution

The router does not call out even if you try a manual call out, you don't see any call activity.

This problem can be due to variety of reasons. If the reasons are not obvious, perform the following step-by-step troubleshooting process.

First, type the following command:

804-isdn#show isdn status

This checks to see if each layer of ISDN is okay.

This step eliminates most issues related to media problems, hardware, cables, ports, SPIDs, and switch-types.

 

Check to see if the interface is down. A quick check of interfaces to determine if any are administratively down can be done using the following command:

804-isdn#show ip interface brief

When it is a new install, it's common for interfaces to be down from the very beginning (by default). Use the previous command to ensure that all interfaces are up.

To bring an interface up, go to the interface configuration mode and enter the following:

804-isdn(config-if)#no shutdown

When you change SPIDs and LDNs, instead of power-cycling the router to re-obtain new TEIs, you can enter the following:

804-isdn#clear interface BRI0

 

Check if the dialer map (dialer string) command exists and is not misconfigured.

 

Check if the rotary group (dialer pool) is configured correctly.

 

Check for a missing dialer-list statement.

 

Check for a missing or misconfigured access control list.

 

Determine if there is a speed-setting mismatch.

Always configure the router with a secondary dialer map for speed 56, or define a class with options 64 and 56.

The second B channel does not come up.

The second channel comes up too early or too late.

Both channels come up together.

There is a missing or misconfigured dialer load-threshold command. Enter the following:

804-isdn#show dialer

Check the configuration of the dialer interface and specifically check if the dialer load-threshold load [outbound | inbound | either] command exists under the dialer interface. Make sure you know how it is configured. This command enables you to configure bandwidth on demand and bring up the second channel if necessary.

Or refer to the configuration command:

804-isdn#show run

With IOS routers, the load is a fraction of 255, multiplied by the bandwidth (128 kbps). In 77x series routers, it is in kbps. So 25 in IOS indicates about 10 percent of configured interface bandwidth, and in 77x, it indicates 25 kbps. If it is configured for either (IOS only) or both (77x only), the router calculates load based on inbound + outbound. Use 1 if you want two channels to come up simultaneously. For cost-savings purposes, it is recommended to use 100 or either.

The line disconnects too slowly.

The line disconnects too quickly.

Check dialer idle-timeout [seconds]. This timer defines the time (in seconds) between two consecutive interesting events. The timer ticks down between these events. When expires, the router is tearing down the call. It is recommended that you use 180 seconds.

Packets wait too long for a different next-hop address.

This occurs when the fast-idle timer is activated. The command does not appear in the config unless it is configured for different values than the default. The default value is 20. It can be seen under the dialer interface.

804-isdn(config-if)#dialer fast-idle [1-2147483]

The router waits too long to connect.

This is probably a configuration issue. If there is no specific configuration, the default value is 30.

Check the configuration command under the dialer interface:

dialer wait-for-carrier-time [1-2147483]

Define or change the amount of time to wait for a carrier to pick up the call after dialing the dial string.

The router waits too long before redial.

This is probably a configuration issue. If there is no specific configuration, the default value is 15 seconds, which is the average time for the switch to release the previous call.

Check the configuration command under the dialer interface:

dialer redial interval [5-2147483]

Define or change the amount of time is seconds for redial interval.


Table 13-4 is not a complete list of all possible issues, but it covers the most common or well-known problems in this category.

NOTE

The bandwidth on demand in ISDN BRI can be configured with one of the most important commands in every dialer configuration:

 804-isdn(config-if)#dialer load-threshold load [outbound | inbound | either] 

Every seconds, the router measures the load in the dialer. The measurement interval is, by default, 300 seconds (5 minutes). To calculate the load at full utilization, the transmission rate of the particular channel is multiplied by the load interval. In general, the rate (input) or (output) is a weighted average calculation that identifies the more-recent load data has more weight in the computation. These computations are made in a time interval called the load interval. To obtain faster results (to bring the interface up faster), or when you test throughput, this interval can be altered.

The 804-isdn(config-if)#load-interval 30 command alters the load interval of any interface from the default to 30 seconds.


To make a call is one of the main functions of an ISDN router. To pass data is another major function. This function can be accompanied by frustrating performance problems, which are covered in the next scenario.




Troubleshooting Remote Access Networks CCIE Professional Development
Troubleshooting Remote Access Networks (CCIE Professional Development)
ISBN: 1587050765
EAN: 2147483647
Year: 2002
Pages: 235

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