Cisco® CCNP Remote Access Exam Cram Notes.

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16.0 WAN Link speeds (typical):

1. Leased lines/ Frame Relay: Up to E3/T3
2. ISDN PRI: E1/T1
3. X.25, ISDN-BRI: 128 Kbps
4. Asynchronous Dial-up: Up to 56/64 Kbps.

17.0 Dialer Interface and Dialer Profiles:

17.1 Dialer Interface: The following are most commonly used optional commands while configuring dialer profile. These commands commonly used with map-class dialer command.

1. Dialer idle-timeout <seconds> - This command is used to specify a disconnect time, if there is no interesting packets for the specified time (in seconds). The default is 120 seconds.

2. Dialer fast-idle <seconds> - This command is used to specify a quick disconnect time if another call is waiting for the same interface, and the interface is idle. It is important to note the difference between the dialer idle-timeout and dialer fast-idle commands. The former disconnects the line even when there is no call waiting in the queue after specified time (120 sec default), the latter disconnects the line even before the idle timer expires, if there is another call waiting in the queue. Obviously, the fast idle timer is of shorter duration than the idle timer.

3. Dialer wait-for-carrier-time - This command is used to wait the carrier for specified time, and to abandon the call if no carrier is detected within specified time. For analog lines, set this for relatively high value.

4. Dialer isdn [speed 56|spc] - This command is used to set the ISDN line speed to 56 Kbps instead of the default 64 Kbps. Spc specifies semi permanent connection.

Note that the command dialer pool-member is used to assign a physical interface to a dialer pool.

Usually, when dialing is in progress the outgoing packets are dropped, since the connection is not yet made. To hold the interesting traffic to be held in a queue, to be sent out as soon as the connection is made use the command

Router(config-if)# dialer hold-queue <number>, where number is number of packets, range 0-100.
holds unto 100 packets of the interesting outgoing traffic in a queue, while the dialing takes place.

17.2 A dialer profile consists of the following required components:

1. Dialer interface - is the logical entity that uses per destination dialer profile. All configuration settings specific to the given destination are defined here. Each dialer interface uses a dialer pool.

2. Dialer pool - Each dialer interface belongs to a dialer pool. A group of physical interfaces associated with a dialer profile constitute a dialer pool.

3. Physical interface - Physical interfaces are configured for encapsulation parameters, and the dialer pool(s) which they belong. A physical interface can belong to multiple dialer pools. The contention for a given physical interface is addresses through the use of priority.

The following component is optional:
Dialer map-class - this is an optional component of dialer profile. A map class is used to specify optional characteristics applicable to various destinations. If a map-class is configured, a dialer interface may simply reference the pertinent map-class during configuration. This eases the administrator of entering the optional configuration commands on each dialer interface.

The command used for creating a dialer profile is:
interface dialer - This global configuration command creates a dialer interface and enters interface configuration mode. Other configuration commands need to be entered at the interface configuration mode for completing the dialer profile.

18.0 X.25:

X.25 maps to the bottom 3 layers of ISO OSI stack. These are: Physical layer, Data Link layer, and Network layer. Also, note that X.25 standards were evolved during the days of analog circuits, where data transfer reliability was poor due to inherent noise of analog transmissions. X.25 is considered over engineered protocol for today's networks, because these days networks are noiseless (employ digital technology end-to-end) compared to analog days. However, X.25 enjoys widespread support and still used in most parts of the world mainly due to installed base and existing infrastructure support.

18.1 When using X.25, the following interface parameters must be set:

1. X.25 encapsulation, use the command:
Router(config-if)# encapsulation x25 [dte | dce];
X.25 DTE is the default. Select DCE if the router is acting as a X.25 switch.

2. X.121 address need to be set. Use the command:
Router(config-if)# x25 address <x.121 address>,
* The first four digits uniquely identify the Data Network and called DNIC (Data Network Identification Code). Out of this, first 3 digits represent the country code. The fourth digit is the provider number. If there are more than 10 providers in a country, a second country code is assigned.
* The Network Terminal Number (NTN) is 8 to 10 or 11 digits long. This number is assigned by the X.25 network provider to the customer, and unique to the network.
The above command assigns the x.121 address to the interface.

3. The x.121 address need to be mapped to a higher layer protocol address, such as IP address. Map command is used for this mapping of X.121 address to its logical address such as IP address.
Associate the X.121 address to its higher layer protocol address such as IP using map statement. The command syntax for this command is:

Router(config-if)#x25 map <protocol> <protocol-address> <x.121 address> [options]
< protocol> can be IP, XNS, DECNET, IPX, AppleTalk etc.
<Protocol-address> is the address of the host at the other end of the PVC
<x.121 address> is the x.121 address of the interface.
Options are used to customize the connection.
The IP address is resolved to X.121 address in the similar manner that it is resolved to MAC address using ARP.

18.2 There are several optional configuration commands that can be set in X.25 environment. Some important commands are given below:

1. R(config-if)# x25 ips <bytes> - This command sets the default maximum input packet size

2. R(config-if)# x25 ops <bytes> - This command sets the default maximum output packet size

3. R(config-if)# x25 win <packets> - This command sets the default window size. The window size determines the maximum number of packets that can be received without sending an acknowledgement.

4. R(config-if)# x25 wout <packets> - this command also sets the default window size. The window size here determines the maximum number of packets that can be sent without receiving an acknowledgement. Note that the number of packets specified in win and wout statements must be one less than the modulus that we discuss in point 5.

5. R(config-if)# x25 modulo <modulus>; modulus can be 8 or 128. The win and wout must be one to one less than the modulus specified here.

19.0 Frame Relay:

I. Important terms used in Frame-Relay:

1. CIR (Committed Information Rate) - this is the rate that the FR switch provider agrees to transfer data.
2. Bc (Committed Burst) - This is the maximum number of bits that a switch provider agrees to transfer during any time Tc, where Tc is the committed rate measurement time.
3. Be (Excess Burst) - This is the maximum number of uncommitted bits that the Frame Relay switch provider attempts to transfer beyond the CIR.
4. Tc (Committed Time interval) - This is the time interval, the time over which, the CIR is averaged.

II. The following are true about Frame-Relay:

1. Cisco routers support two types of encapsulations, a) cisco b) ietf
Use ietf if you are communication with a non Cisco router.
2. The encapsulation type can be configured either at interface lever or on per-destination level.
3. The command 'frame-relay map' is used for static address mapping.
4. Cisco IOS allows FR address mapping to be done either statically (manually) or dynamically (if the FR environment supports).

III. Note the following points about Frame Relay DLCIs:

1. DLCIs (Data Link Connection Identifier) have only local signification. It means, the end devices over FR network can have can different DLCI numbers.
2. DLCI number is provided by the FR service provider. DLCI number is mapped to Layer 3 protocol address using 'frame-relay map' statement.
3. Typically, the DLCIs 0 to 15 and 1008 to 1023 are reserved for special purposes. Service providers are assigned DLCIs 16 through 1007.
4. DLCIs 1019, 1020 can be used by multicasts.

IV. LMI (Link Management Interface) is a signaling standard between the CPE (Customer Premise Equipment) and the FR switch.

Cisco IOS supports the following three types of LMIs:

1. Cisco - This LMI type is jointly developed by Cisco, Stratacom, Northern Telecom, and DEC.

2. Ansi - ITU-T

3. Q.933a standard.

One of the above three LMI types need to be selected for FR to work.

The correct syntax for specifying LMI-type for use by FR switch is:
frame-relay lmi-type {ansi | cisco | q933a }
cisco is the default lmi type.

For specifying ansi lmi-type, use the following command at interface configuration mode:
frame-relay lmi-type ansi

V. The syntax of command for enabling frame-relay encapsulation on Cisco routers is:
Router1(config-if)# encapsulation frame-relay [cisco | ietf]
Note that cisco is the default encapsulation type selected, if you don't specify any.
If communication with a non-Cisco router, select ietf as the encapsulation type.

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