Cisco® CCNP Remote Access Exam Cram Notes.

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20.0 Traffic Shaping:

Given below are the normal sequence of steps and relevant commands that are required in enabling Frame Relay traffic shaping:

1. Specify the map class name - Use the command
R(config)# map-class frame-relay <map-class-name>, where <map-class-name> is the name of map class.

2. Define map class - Typical configuration steps here may include:
A) Enabling rate enforcement by defining average and peak rates of traffic.
B) Specifying a custom queue list for the map class
C) Specifying a priority queue list for the map class.
D) Enabling BECN feedback to throttle the output rate on any SVC for the map class. 
All the above (A through D) are optional configuration commands.

3. Enable Frame Relay on an interface by issuing interface configuration command:
R(config-if)#encapsulation frame-relay
Note that the default encapsulation type is cisco.

4. Next, enable frame relay traffic shaping on an interface by issuing the command:
R(config-if)# frame-relay traffic-shaping

5. Specify a Traffic Shaping Map Class for the Interface by issuing the following command:
R(config-if)# frame-relay class <map-class-name>, where <map-class-name> is the map class name.
Specifying a Frame Relay map class for a main interface, results in all the VCs on its sub interfaces inherit all the traffic shaping parameters defined for the class.

Traffic shaping is recommended under the following circumstances:

1. If a FR network consists of high speed connections at the central site and low speed connections (less than 64 Kbps) at branch offices, bottlenecks may occur at slow links. Traffic shaping is useful to address this problem.

2. If the FR network occasionally get congested, traffic can be throttled using BECN, so that the congestion is overcome. Note that the traffic shaping may not be useful when a FR network consistently encounters congestion due to insufficient bandwidth.

3. Also, if the FR network has to carry different types of protocols, such as IP, SNA it is recommended to enable traffic shaping. This would allow the prioritization of time sensitive traffic.

Frame Relay traffic shaping can be achieved through the following means:

1. By using rate enforcement - Here the average and peak data rates are defined by using the command:
R(config-map-class)# frame-relay traffic-rate <average> [peak],
where <average> is the average rate in bps, which is equivalent to the CIR.
Peak is optional command - specifies the peak rate in bps.

2. Adaptive shaping through the use of BECN by using the following command:
R(config-map-class)# frame-relay adaptive-shaping becn
The above command enables the router to dynamically adjust the rate at which it sends packets, depending on the BECNs received.

3. Traffic shaping through use of custom queuing:
Custom queuing is recommended when a particular protocol or service needs to be given guaranteed transmission rate. The command that enables custom queuing is:
R(config-map-class)# frame-relay custom-queue-list <list-number>

4. Traffic shaping through use of priority queuing:
Priority queuing allows absolute priority to be assigned to a protocol or service. The command that enables priority queue list is:
R(config-map-class)# frame-relay priority-group <list-number>
Both custom-queue-list and priority-queue-list commands require that you have previously defined a custom queue or priority queue respectively.
Only one form of queuing may be associated with a given map class.

21.0 Back-up Interface configuration:

The backup interface configuration involves the following steps:

1. Configure the primary interface as needed.

2. Configure the backup (secondary) interface using the command:
R(config-if)# backup interface <interface-type number>, where <interface-type-number> is the interface port or slot/port number.

An example, for assigning BRI0 as the backup, use the command:
R(config-if)# backup interface bri0

3. Specify the time to wait before enabling the backup link after the primary link goes down with the command:
R(config-if)# backup delay {enable-delay} | never} {disable-delay | never}
enable-delay - is the number of seconds that elapse after the primary link goes down and before the secondary (backup) link is activated.
Disable-delay - is the number of seconds that elapse after the primary line comes up, and before the secondary (backup) link is deactivated.
Never - prevents the secondary line from being activated or deactivated.

The following statements are true with respect to backup lines:

1. The command 'backup interface' is used for configuring an interface for backup operation.

2. A backup line can be configured to be activated based on the traffic load on the primary line, such that the backup is activated if the load on primary exceeds certain percentage of available bandwidth.

3. When an interface is configured as backup interface to a primary line, the backup route does not appear in the routing table. However, if the primary line fails, and the backup is activated, then the backup route shows up in the route table.

4. If a BRI is used for dial backup, none of the two B channels are available while the interface is in standby mode. This can be overcome by using dialer profiles. Two dialer profiles can be defined, one for the backup line and the other for regular dial up. Physical BRI interface can be made member of both the dialer pools. Under these conditions, both B channels can be used, one for the backup line and the other for regular dial up.

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