Ccna configuracion y comandos

Reference for commands for Cisco products

http://www.cisco.com/univercd/home/home.htm
CLI Password Configuration

Cisco IOS Software Command Help

IOS stores the commands that you type in a history buffer, storing ten commands by default. You can
change the history size with the terminal history size x user exec command, where x is the number of
commands for the CLI to recall; this can be set to a value between 0 and 256. You then can retrieve
commands so that you do not have to retype the commands.

Key Sequences for Command Edit and Recall

IOS enables enhanced editing mode by default and has for a long time. However, you can turn off these
keystrokes with the no terminal editing exec command, and turn them back on with the terminal
editing command.

CLI Configuration Mode Versus Exec Modes

Cisco Router Memory Types

Locations for Copying and Results from Copy Operations

Configuration show Commands

Getting into Setup Mode

The Cisco IOS Software Boot Sequence
1. The router performs a power-on self-test (POST) to discover and verify the hardware.
2. The router loads and runs bootstrap code from ROM.
3. The router finds the IOS or other software and loads it.
4. The router finds the configuration file and loads it into running config.

Three OS Categories for Routers

Two configuration tools tell the router what OS to load:
X The configuration register
X The boot system configuration command

On most Cisco routers, the default Configuration Register setting is hexadecimal 2102.

Binary Version of Configuration Register, Value Hex 2102

The boot field is the name of the low-order 4 bits of the configuration register. This field can be considered
a 4-bit value, represented as a single hexadecimal digit. (Cisco represents hexadecimal values by preceding
the hex digit[s] with 0x—for example, 0xA would mean a single hex digit A.) If the boot field is hex 0,
ROMMON is loaded. If the boot field is hex 1, RXBOOT mode is used. For anything else, it loads a full-
featured IOS. But which one?
The second method used to determine where the router tries to obtain an IOS image is through the use of
the boot system configuration command. If the configuration register calls for a full-featured IOS (boot
field 2-F), the router reads the startup-configuration file for boot system commands. If there are no boot
system commands, the router takes the default action, which is to load the first file in Flash memory. Table
7-6 summarizes the use of the configuration register and the boot system command at initialization time,
when the boot field’s value implies that the router will look for boot commands.

The Boot System Commands

Impact of the boot system Command on Choice of IOS: Boot Field Between 2 and F

Operating Cisco LAN Switches
2950 Front Panel and LEDs

2950 Switch LEDs and Meaning

Basic Router Configuration and
Operation
Configuring IP Addresses
IP Configuration Commands

Basic Administrative Configuration
On most routers, you would configure at least the following:
X A host name for the router
X Reference to a DNS so that commands typed on the router can refer to host names instead of IP addresses
X Set a password on the console port
X Set a password for those Telnetting to the router
X Set the enable secret password to protect access to privileged mode
X Create a banner stating an appropriate warning, depending on the security practices at that company

To make the router ask for a password at the console, you need the login console subcommand; the
password console subcommand tells the router what password is required at the console. Similar logic
applies to the login and password vty subcommands.
Two other things that you might want to configure habitually on routers are the console timeout and the
synchronization of unsolicited messages. The exec timeout minutes seconds command sets the inactivity
timeout. Also, unsolicited informational messages and output from the IOS debug command both show up
at the console by default. These same messages can be seen at the aux port or when Telnetting into a router
by using the terminal monitor command. The logging synchronous line subcommand tells the router
not to interrupt the output of a show command with these unsolicited messages, letting you read the output

of the command that you typed before the router displays the other messages. logging synchronous can
make your life a lot easier when using a router.

Syslog messages also can be sent to another device. Two alternatives exist: sending the messages
to a syslog server, and sending the messages as SNMP traps to a management station. The
logging host command, where host is the IP address or host name of the syslog server, is used
to enable sending messages to the external server. After SNMP is configured, the snmp-server
enable traps command tells the IOS to forward traps, including syslog messages.

Configuring IP Addresses
The ip address interface subcommand configures the IP address for each interface. Because each interface
has an IP address, the interface configuration command precedes each ip address command, identifying
to IOS the interface to which the IP address should be assigned.

Prefix Notation
This notation, called prefix notation, denotes the subnet mask in terms of the number of 1 bits in the subnet
mask. The number of bits of value binary 1 in the mask is considered to be the prefix. Prefix notation is
simply a shorter way to write the mask.
If you prefer to see the subnet masks instead of the prefix, simply use the terminal ip netmask-format
decimal exec command.

Seeding the Routing Table with Connected IP Routes
The Cisco IOS routes IP packets by default—in other words, you do not need to type any commands to tell
the router to enable IP routing. Before the router will route packets in or out an interface, the interface must
have an IP address.
The problem with the configurations shown so far is that the routers do not know routes to all the subnets in
the network. The ultimate solution to this problem is to configure a dynamic routing protocol.
Routers add routes to their routing tables for the subnets associated with their own physical interfaces.

The show ip route command lists routes to the subnets connected to the router. The output from the
command lists a C in the first column, which, according to the notes at the beginning of the command
output, means “connected.” In other words, this router is connected directly to these subnets.

The show ip interfaces brief command lists one line per interface, with IP address information and
interface status.

The show interfaces {interface} command lists more details about a single interface, with most of those
details about the interface itself. Finally, the show ip interfaces {interface} command shows
detailed information about the IP protocol running over interface.

IOS adds connected routes to the routing table that meet the following requirements:
X The interface has been configured with a valid IP address.
X The interface is in an up and up status according to the various interface-oriented show commands.

All three of the show commands that list interface status information use two designations of up and up.
The first status keyword (the first of the two ups in this case) generally refers to OSI Layer 1 status. The
second status word generally refers to the status of OSI Layer 2.
Another instance in which a router might put an interface in status up and down is when the router does not
receive keepalive messages on a regular basis. Cisco routers send, and expect to receive, proprietary
keepalive messages on each interface. The purpose of the keepalives is to know whether the interface is
usable. You can disable keepalives with the no keepalive interface subcommand, or you can change the
timer with the keepalive interval interface subcommand.

To bring down an interface for administrative reasons and, as a side effect, remove the connected route
from the routing table, you can use the shutdown interface subcommand. The no shutdown command
brings the interface back up.

Bandwidth, Clock Rate, and Serial Lines in the Lab
To use a back-to-back WAN connection, one router must supply the clocking. The clock rate command
sets the rate in bits per second on the router that has the DCE cable plugged into it. If no cable has been
plugged in, the IOS accepts the command. If a DTE cable has been plugged in, IOS rejects the command. If
you do not know which router has the DCE cable in it, you can find out by using the show controllers
command.

The bandwidth command tells IOS the speed of the link, in kilobits per second, regardless of whether the
router is supplying clocking. The bandwidth setting does not change anything that the router does at Layer
1; instead, this setting is used by IOS software for other purposes. bandwidth defaults to T1 speed on
serial interfaces. There is no default for clock rate, even with a DCE cable plugged in—it must be
configured.

IP Troubleshooting Features
Internet Control Message Protocol
TCP/IP includes a protocol specifically to help manage and control the operation of a TCP/IP network,
called the Internet Control Message Protocol (ICMP). The ICMP protocol provides a wide variety of
information about the health and operational status of a network. The ICMP messages sit inside an IP
packet, with no transport layer header at all–so it is truly just an extension of the TCP/IP network layer.

ICMP Message Types

ICMP Echo Request and Echo Reply
The ICMP echo request and echo reply messages are sent and received by the ping command.
The echo request includes some data that can be specified by the ping command; whatever data is sent in
the echo request is sent back in the echo reply.

Destination Unreachable ICMP Message
The ICMP Destination Unreachable message is sent when a message cannot be delivered completely to the
application at the destination host. Because packet delivery can fail for many reasons, there are five
separate unreachable functions (codes) using this single ICMP unreachable message. All five code types
pertain directly to an IP, TCP, or UDP feature.

ICMP Unreachable Codes

Codes That the ping Command Receives in Response to Its ICMP Echo Request

IP Naming Commands
IP Naming Commands

Telnet and Suspend
The telnet IOS exec command enables you to Telnet from one Cisco device to another; in practical use, it
is typically to another Cisco device. One of the most important features of the telnet command is the
suspend feature.

Telnet Command Options

Cisco Discovery Protocol
The Cisco Discovery Protocol (CDP) discovers basic information about neighboring routers and switches,
without needing to know the passwords for the neighboring devices. CDP supports any LAN, HDLC,
Frame Relay, and ATM interface—in fact, it supports any interface that supports the use of SNAP headers.
The router or switch can discover Layer 2 and Layer 3 addressing details of neighboring routers without
even configuring that Layer 3 protocol—this is because CDP is not dependent on any particular Layer 3
protocol.
Devices that support CDP advertise their own information and learn information about others by listening
for their advertisements. On media that support multicasts at the data link layer, CDP uses multicast; on
other media, CDP sends a copy of the CDP update to any known data-link addresses. So, any CDP-

supporting device that shares a physical medium with another CDP-supporting device can learn about the
other device.

CDP discovers several useful details from the neighboring device:
X Device identifier—Typically the host name
X Address list—Network and data-link addresses
X Port identifier—Text that identifies the port, which is another name for an interface
X Capabilities list—Information on what type of device it is—for instance, a router or a switch
X Platform—The model and OS level running in the device

CDP is enabled in the configuration by default. The no cdp run global command disables CDP for the
entire device, and the cdp run global command re-enables CDP. Likewise, the no cdp enable interface
subcommand disables CDP just on that interface, and the cdp enable command switches back to the
default state of CDP being enabled.

The show cdp command has four options. THe show cdp neighbor command lists each neighbor, with
one line of output per neighbor. The show cdp entry fred command lists the details learned by CDP about
the neighbor whose host name is fred. Another command that lists the detailed information is the show
cdp neighbor detail command, which is in the same format as show cdp entry but lists the information
for every neighbor.

Turning off CDP
no cdp run (general)
no cdp enable (para una interface)

Gathering CDP Timers and Holdtime Information
show cdp
cdp timer
cdp holdtime

Gathering Neighbor Information
show cdp neighbor
show cdp neighbor detail
show cdp entry *

Gathering Interface Traffic Information
show cdp traffic

Gathering Port and Interface Information
show cdp interface

Managing Configuration Files
copy source destination
The source and the destination parameters can be running-config, startup-config, or
tftp for RAM, NVRAM, and a TFTP server respectively.

Two commands can be used to erase the contents of NVRAM. These are the write erase
command, which is the older command, and the erase startup-config command, which is the
newer command.

Verifying Flash Memory
show flash

Backing Up the Cisco IOS

copy flash tftp

Restoring or Upgrading the Cisco IOS Software
copy tftp flash
the router must be reloaded.

Backing Up and Restoring the Cisco Configuration
copy run start
copy running-config tftp
copy startup-config tftp
show running-config

Static Routing
ip route destination_ip_address subnet_mask { ip-address | interface } [
distance ]

Verifying Routing Tables
show ip route
clear ip route

Configuring OSPF
The commands used to configure OSPF are:
• router ospf < process_number > where process_number is a number local to the
router. This command configures OSPF as the routing protocol on the router.
• network network_number wildcard_mask defines the networks that are to participate
in the OSPF updates and the area that they reside in.
• interface loopback < interface_number > ip address < ip_address > <
subnet_mask >defines a loopback interface, which is a virtual interface, on the router.
• ip ospf cost < cost > sets the default cost for the router.
• auto-cost reference-bandwidth changes the OSPF cost formula.
Note: The ip ospf cost command overrides the auto-cost reference-bandwidth
command.

Configuring EIGRP
The commands used to configure EIGRP on a Cisco router are consistent with the other IP
routing protocol
commands. The EIGRP commands are:
• router eigrp autonomous_system_number configures EIGRP as the routing protocol
on the router.
• network network_number [ wildcard_mask ] defines the networks that are to
participate in the EIGRP updates. The [ wildcard_mask ] optional parameter identifies
which interfaces are running EIGRP.
• no network network_number [ wildcard_mask ] disables EIGRP.
• no autosummary turns off automatic summarization.
• ip summary address eigrp autonomous_system_number ip_address subnet_mask
configures summarization at the interface level.
• variance multiplier configures EIGRP to load-balance across unequal paths.
• bandwidth line_speed overrides the default bandwidth settings on the links.

VTP Configuration

Before VLANs can be configured, VTP must be configured.

Configuring a VTP Management Domain
• Switch# vlan database
• Switch(vlan)# vtp domain domain_name
To assign a switch to a management domain on a CLI-based switch,
• Switch(enable) set vtp [ domain domain_name ]

Configuring the VTP Mode
• Switch(vlan)# vtp domain domain_name
• Switch(vlan)# vtp { server | client | transparent }
• Switch(vlan)# vtp password password
On a CLI-based switch, the following command can be used to configure the VTP mode:
• Switch(enable) set vtp [ domain domain_name ] [ mode{ server | client |
transparent }] [ password password ]

Configuring the VTP Version
• Switch(vlan)# vtp v2-mode
On a CLI-based switch, the VTP version number is configured using the following command:
• Switch(enable) set vtp v2 enable

Standard IP Access List Configuration
• ip access-group {number | action [in | out]}, in which action can be either
permit of deny and is used to enable access lists; and
• access-class number | action [in | out], which can be used to enable either
standard or extended access lists.

The standard access list configuration can be verified using the following show commands:
• show ip interface[type number], which includes a reference to the access lists
enabled on the interface;
• show access-lists [access-list-number | access-list-name], which shows
details of configured access lists for all protocols; and
• show ip access-list [access-list-number | access-list-name], which shows
the access lists.

Extended IP Access Control Lists
• access-list access-list-number action protocol source source-wildcard
destination destination-wildcard [log | log-input], which can be used to
enable access lists;

Basic Configuration and Operation Commands for the Cisco
2950 Switch
Commands for Catalyst 2950 Switch Configuration

Basic Switch Operation
Popular show Commands on a 2950 Switch

show interfaces fastethernet 0/13 command lists basic status and configuration information about
fastethernet interface 0/13.

show interfaces status lists the status of each interface in a single line, including the speed and duplex
settings negotiated on that interface.

show mac-address-table dynamic command lists all the dynamically learned entries in the bridging
table.

show mac-address-table shows both static and dynamic entries.

show running-config command lists the default configuration.

show startup-config

erase startup-config

copy running-config startup-config

copy running-config startup-config

reload

Typical Basic Administrative Configuration
Basic Configuration of a 2950 Switch

hostname name

password password for the consol and vty(telnet)

login commands tell the switch to require a password at the console and for Telnet sessions,

enable password password

enable secret password

interface Fastethernet 0/5 command to enter interface configuration mode.

duplex and speed commands tell the switch to force these settings rather than use the autonegotiated
settings.

shutdown puts an interface in a down status administratively

no shutdown command brings the interface back up

To configure the IP address, you first use the interface vlan 1 command, Next, the ip address command
sets the IP address and subnet mask.

ip default-gateway sets the default IP gateway for the switch

Port Security Configuration
To configure port security, you need to configure several things. You enable port security using the
switchport port-security interface configuration command. Also, the 2950 switch IOS allows port
security only on ports that do not connect to other switches. To designate an interface as not connecting to
another switch, you use the switchport mode access command. Then you can statically configure the
MAC addresses using the switchport portsecurity mac-address mac-address command.

Using Port Security to Define Correct MAC Addresses of Particular Interfaces

switchport port-security mac-address

switchport mode access
switchport port-security
switchport port-security maximum you can configure up to 132 per interface using the switchport port-
security maximum command.
switchport port-security violation
switchport portsecurity mac-address sticky tells the switch to learn the MAC address from the first
frame sent into the switch, and then add the MAC address as a secure MAC to the running configuration
show port-security interface fastethernet 0/1
show running-config

Spanning Tree Protocol Configuration
Cisco switches use STP by default.

Configuration and Operations Commands from This Chapter for 2950 Switches

Basic STP show Commands
STP Status for the Network Shown in Figure 2-12 with Default STP Parameters

show spanning-tree

Changing STP Port Costs and Bridge Priority
Manipulating STP Port Cost and Bridge Priority

spanning-tree cost 2

show spanning-tree

spanning-tree vlan 1 root primary

EtherChannel Configuration
Configuring and Monitoring EtherChannel

channel-group 1 mode on

show etherchannel 1 summary

VLAN and Trunking Configuration
2950 VLAN Command List

VLAN Configuration for a Single Switch

Cisco 2950 switches use a slightly different configuration mode to configure VLAN and VTP information
as compared to the other switch configuration commands. You use VLAN configuration mode, which is
reached by using the vlan database enable mode EXEC command. So, instead of using the configure
terminal enable mode command, you enter vlan database, after which you are placed in VLAN
configuration mode. In VLAN configuration mode, you can configure VLAN information as well as VTP
settings.

vlan database

vlan 2 name barney-2

exit

apply

abort

switchport access vlan 2

switchport mode access

interface range fastEthernet 0/9 - 12

switchport access vlan 3

if you had entered just the switchport access vlan commands before creating the VLANs in VLAN
configuration mode, the switch would have automatically created the VLANs.

show vlan brief

show vlan

show vlan id 2

VLAN Trunking Configuration
Network with Two Switches and Three VLANs

switchport mode dynamic desirable

2950 Trunk Configuration Options with the switchport mode Command

vtp domain fred

show vtp

show interfaces fastEthernet 0/17 switchport

show interfaces fastEthernet 0/17 trunk

Configuring and Testing Static Routes
Sample Network Used in Static Route Configuration Examples

Configuring RIP and IGRP
IP RIP and IGRP Configuration Commands

IP RIP and IGRP EXEC Commands

Basic RIP and IGRP Configuration
Sample Router with Five Interfaces

Completing the RIP Configuration from Example

IGRP Configuration

Finally, the numbers between the brackets mention some very useful information. The first number
represents the administrative distance, which is covered later in this chapter. The second number lists the
metric associated with this route.

IGRP uses the value set with the bandwidth command on each interface to determine the interface’s
bandwidth. On LAN interfaces, the bandwidth command’s default values reflect the correct bandwidth.
However, on serial interfaces, the bandwidth command defaults to 1544—in other words, T1 speed. (The
bandwidth command uses units of kbps, so the bandwidth 1544 command sets the bandwidth to 1544
kbps, or 1.544 Mbps.)

Examination of RIP and IGRP debug and show Commands
Sample Three-Router Network with Subnet 10.1.2.0 Failing

The following list describes what happens at each point in the process:
X POINT NUMBER 1—Albuquerque sends an update out Serial0, obeying split-horizon rules. Notice that
10.1.2.0, Yosemite’s Ethernet subnet, is not in the update sent out Albuquerque’s S0 interface.
X POINT NUMBER 2—This point begins right after Yosemite’s E0 is shut down, simulating a failure.
Albuquerque receives an update from Yosemite, entering Albuquerque’s S0 interface. The route to 10.1.2.0
has an infinite metric, which in this case is 16.
X POINT NUMBER 3—Albuquerque formerly did not mention subnet 10.1.2.0 because of split-horizon
rules (point 1). The update at point 3 includes a poisoned route for 10.1.2.0 with metric 16. This is an
example of split horizon with poison reverse.
X POINT NUMBER 4—Albuquerque receives an update in S1 from Seville. The update includes a metric
16 (infinite) route to 10.1.2.0. Seville does not suspend any splithorizon rules to send this route, because it
saw the advertisement of that route earlier, so this is a simple case of route poisoning.

Migrating to IGRP with Sample show and debug Commands

Issues When Multiple Routes to the Same Subnet Exist
By default, Cisco IOS software includes up to four equal-cost routes to the same subnet in the routing table
—essentially as if maximum-paths 4 had been configured. You can configure maximum-paths as low
as 1 or as high as 6.

When RIP places more than one route to the same subnet in the routing table, the router balances the traffic
across the various routes.

The metric formula used for IGRP (and EIGRP) poses an interesting problem when considering equal-
metric routes. IGRP can learn more than one route to the same subnet with different metrics; however, the

metrics are very unlikely to be equal, because the metric is actually calculated with a mathematical
formula. So, with IGRP (and EIGRP), you can tell the routing protocol to think of metrics that are “pretty
close” as being equal. To do so, Cisco IOS software uses the variance router subcommand to define how
different the metrics can be for routes to be considered to have equal metrics.

The variance command defines a multiplier; any metrics lower than the product of the lowest metric and
the variance are considered equal.

When IGRP places more than one route to the same subnet in the routing table, the router balances the
traffic across the various routes in proportion to the metric values. You can choose to tell the router to use
only the lowest-cost route using the traffic-share min router IGRP subcommand. This command tells the
router that, even if multiple routes to the same subnet are in the routing table, it should use only the route
that truly has the smallest metric.

OSPF Configuration
IP OSPF Configuration Commands

IP OSPF EXEC Commands

OSPF Single-Area Configuration
Sample Network for OSPF Single-Area Configuration

router ospf 1

network

OSPF Configuration with Multiple Areas
Multiarea OSPF Network

OSPF Multiarea Configuration and show Commands on Albuquerque

OSPF Multiarea Configuration and show Commands on Yosemite

network 10.1.4.1 0.0.0.0 area 1

show ip route ospf

show ip route

The OSPF topology database includes information about routers and the subnets, or links, to which they are
attached. To identify the routers in the neighbor table’s topology database, OSPF uses a router ID (RID) for
each router. A router’s OSPF RID is that router’s highest IP address on a physical interface when OSPF
starts running. Alternatively, if a loopback interface has been configured, OSPF uses the highest IP address
on a loopback interface for the RID, even if that IP address is lower than some physical interface’s IP
address. Also, you can set the OSPF RID using the router-id command in router configuration mode.

router-id

NOTE If you’re not familiar with it, a loopback interface is a special virtual interface in a Cisco router. If
you create a loopback interface using the interface loopback x command, where x is a number, that
loopback interface is up and operational as long as the router IOS is up and working. You can assign an IP
address to a loopback interface, you can ping the address, and you can use it for several purposes—
including having a loopback interface IP address as the OSPF router ID.

show ip ospf neighbor

show ip ospf interface

ip ospf cost x

bandwidth

auto-cost reference-bandwidth 1000

EIGRP Configuration
IP EIGRP Configuration Commands

IP EIGRP EXEC Commands

router eigrp

network

show ip route

show ip route eigrp

show ip eigrp neighbors

show ip eigrp interfaces

NAT Configuration
NAT Configuration Commands

NAT EXEC Commands

Static NAT Configuration
NAT IP Address Swapping: Unregistered Networks

ip nat inside

ip nat outside

show ip nat translations

show ip nat statistics

Dynamic NAT Configuration

The configuration for dynamic NAT includes a pool of inside global addresses, as well as an IP access list
to define the inside local addresses for which NAT is performed.

ip nat pool

ip nat inside source

ip nat inside source list 1 pool fred

ip nat pool fred

show ip nat translations

show ip nat statistics

clear ip nat translation

clear ip nat translation *

debug ip nat

NAT Overload Configuration (PAT Configuration)
NAT Overload and PAT

ip nat inside source list 1 interface serial 0/0 overload

show ip nat translations,

HDLC and PPP Configuration
PPP and HDLC Configuration Commands

Point-to-Point-Related show and debug Commands

encapsulation hdlc

no encapsulation ppp,

CHAP Configuration Example

ISDN Configuration and Dial-on-Demand Routing
ISDN Configuration Commands

ISDN-Related EXEC Commands

DDR Legacy Concepts and Configuration
You can configure DDR in several ways, including Legacy DDR and DDR dialer profiles. The main
difference between the two is that Legacy DDR associates dial details with a physical interface, whereas
DDR dialer profiles disassociate the dial configuration from a physical interface, allowing a great deal of
flexibility.

DDR Step 1: Routing Packets Out the Interface to Be Dialed
Sample DDR Network

DDR does not dial until some traffic is directed (routed) out the dial interface.

The router needs to route packets so that they are queued to go out the dial interface. Cisco’s design for
DDR defines that the router receives some user-generated traffic and, through normal routing processes,
decides to route the traffic out the interface to be dialed.

Of course, routing protocols cannot learn routes over a BRI line that is not normally up! Therefore, static
routes must be configured on SanFrancisco, pointing to subnets in LosAngeles. Then, packets are routed
out the interface, which can trigger a dial of a B channel to LosAngeles.

To begin the process of building a DDR configuration, IP routes are added to the configuration so that
packets can be directed out BRI0 on SanFrancisco,

DDR Step 2: Determining the Subset of the Packets That Trigger the Dialing Process
Together, Steps 1 and 2 of Legacy DDR logic determine when to dial a circuit. These combined steps are
typically called triggering the dial. In Step 1, a packet is routed out an interface to be dialed, but that alone
does not necessarily cause the dial to occur. The Cisco IOS software allows Step 2 to define a subset of the
packets routed in Step 1 to actually cause the route to dial.

Cisco calls packets that are worthy of causing the device to dial interesting packets. Cisco does not name
packets that are not worthy of causing the dial; Only interesting packets cause the dial to occur, but when
the circuit is up, both interesting and boring traffic can flow across the link.

Two different methods can be used to define interesting packets. In the first method, interesting is defined
as all packets of one or more Layer 3 protocols (for example, all IP packets). The second method allows
you to define packets as interesting if they are permitted by an access list.

DDR Step 3: Dialing (Signaling)
Before the router can dial, or signal, to set up a call, it needs to know the phone number of the other router.
The command is dialer string string, where string is the phone number.

With only one site to dial, you can simply configure a single dial string. However, with multiple remote
sites, the router needs to know each site’s phone number. It also needs to know which phone number to use
when calling each site.

Mapping Between the Next Hop and the Dial String

Two other important configuration elements are included in Example 10-4. First, CHAP authentication is
configured. PAP or CHAP is required if you’re dialing to more than one site with ISDN—and PAP and
CHAP require PPP. Notice that the usernames and password used with the two remote routers are shown
near the top of the configuration.

You should also note the importance of the broadcast keyword on the dialer map commands. Just as with
any other point-to-point serial link, there is no true data-link broadcast. If a broadcast must be sent on the
interface after the circuit has been created, you must use the broadcast keyword to tell the interface to
forward the packet across the link.

DDR Step 4: Determining When the Connection Is Terminated
The decision to take down the link is the most interesting part about what happens while the link is up.
Although any type of packet can be routed across the link, only interesting packets are considered worthy
of keeping the link up and spending more money. The router keeps an idle timer, which counts the time
since the last interesting packet went across the link. If no interesting traffic happens for the number of
seconds defined by the idle timer, the router brings the link down.
Two idle timers can be set. With the dialer idle-timeout seconds command, the idle time is set. However,
if the router wants to dial other sites based on receiving interesting traffic for those sites, and all the B
channels are in use, another shorter idle timer can be used. The dialer fast-idle seconds command lets you
configure a typically lower number than the idle timer so that when other sites need to be dialed, the link
that is currently up can be brought down more quickly.

ISDN BRI Configuration
Completed SanFrancisco Configuration

LosAngeles Configuration: Receive Only

isdn switch-type

isdn spid1

isdn spid2

Summary of the New Configuration Needed for ISDN BRI Beyond Legacy DDR Configuration

Summary of Legacy DDR Configuration
Summary Legacy DDR Configuration Commands

ISDN and DDR show and debug Commands
SanFrancisco DDR Commands

show dialer interface bri 0,

show isdn active

show isdn status

debug isdn q921

debug isdn q931

debug dialer packets

ISDN PRI Configuration
To configure ISDN BRI, you need to configure only the switch type, plus the SPIDs if the service provider
needs to have them configured.

X Configure the type of ISDN switch to which this router is connected.
X Configure the T1 or E1 encoding and framing options (controller configuration mode).
X Configure the T1 or E1 channel range for the DS0 channels used on this PRI (controller configuration
mode).
X Configure any interface settings (for example, PPP encapsulation and IP address) on the interface
representing the D channel.

Configuring a T1 or E1 Controller
PRI Controller Configuration Example

Full PRI Configuration
PRI Controller Configuration Example: Completed Configuration on SanFrancisco

The most unusual part of the configuration introduces the concept of actually identifying the D channel in
the interface command. Notice the command interface serial 1/0:23. The :x notation, where x identifies
one of the channels inside the PRI, tells the IOS which of the 24 channels you want to configure. The DDR
interface subcommands should be configured on the D channel, which is channel 23 according to the
command! The interface command numbers the channels from 0 through 23, with the D channel as the
last channel, so the :23 at the end correctly tells IOS that you are configuring details for the 24th channel—
the D channel.

Summary of the New Configuration Needed for ISDN PRI Beyond Legacy DDR Configuration

DDR Configuration with Dialer Profiles
Legacy DDR with Two BRIs and Eight Remote Sites

The problem with Legacy DDR in this case is that it cannot be configured to dial all eight sites using any
available B channel on either BRI.

Dialer profiles overcome this problem with Legacy DDR using a slightly different style of DDR
configuration. Dialer profiles pool the physical interfaces so that the router simply uses an available B
channel on any of the BRIs or PRIs in the pool. Dialer profile configuration allows the Central Site router
to dial any of the eight remote routers using either of the BRIs

Dialer Profiles: Pooling Multiple BRIs to Reach Eight Remote Sites

Summary of the New Configuration Needed for Dialer Profiles Versus Legacy DDR

SanFrancisco Configuration Migrated to Use Dialer Profiles and Two BRIs

ip route

isdn switch-type

dialer-list 2

switch-type

dialer pool-member 3

Dialer Profiles: Pooling Multiple BRIs

Multilink PPP
Multilink PPP Configuration for Atlanta

ppp multilink

dialer load-threshold.

Summary of the New Configuration Needed for MLP Versus Legacy DDR

Summary Legacy DDR Configuration Commands

Summary of the New Configuration Needed for ISDN BRI Beyond Legacy DDR Configuration

Summary of the New Configuration Needed for ISDN PRI Beyond Legacy DDR Configuration

Summary of the New Configuration Needed for Dialer Profiles Versus Legacy DDR

Summary of the New Configuration Needed for MLP Versus Legacy DDR

Frame Relay Configuration
Frame Relay Configuration Commands

Frame Relay-Related EXEC Commands

A Fully-Meshed Network with One IP Subnet

Mayberry Configuration

Mount Pilot Configuration

Raleigh Configuration

Yes, Frame Relay configuration can be that easy, because IOS uses some very good choices for default
settings:
X The LMI type is automatically sensed.
X The encapsulation is Cisco instead of IETF.
X PVC DLCIs are learned via LMI status messages.
X Inverse ARP is enabled (by default) and is triggered when the status message declaring that the VCs are
up is received. (Inverse ARP is covered in the next section.)

In some cases, the default values are inappropriate. For example, you must use IETF encapsulation if one
router is not a Cisco router. For the purpose of showing an alternative configuration, suppose that the
following requirements were added:
X The Raleigh router requires IETF encapsulation on both VCs.
X Mayberry’s LMI type should be ANSI, and LMI autosense should not be used.

Mayberry Configuration with New Requirements

Raleigh Configuration with New Requirements

Frame Relay Address Mapping
Frame Relay “mapping” creates a correlation between a Layer 3 address and its corresponding Layer 2
address.

Full Mesh with IP Addresses

show Commands on Mayberry, Showing the Need for Mapping

Mayberry can use two methods to build the mapping shown. One uses a statically configured mapping, and
the other uses a dynamic process called Inverse ARP.

Inverse ARP is enabled by default in Cisco IOS software Release 11.2 and later.

frame-relay map Commands

A Partially-Meshed Network with One IP Subnet Per VC
Partial Mesh with IP Addresses

Atlanta Configuration

Charlotte Configuration

Nashville Configuration

Boston Configuration

Output from EXEC Commands on Atlanta

A Partially-Meshed Network with Some Fully-Meshed Parts
Hybrid of Full and Partial Mesh

Router A Configuration

Router B Configuration

Router C Configuration

Router D Configuration

Router E Configuration

IP Addresses with Point-to-Point and Multipoint Subinterfaces

Frame Relay Maps and Inverse ARP on Router C

Standard IP Access List Configuration
Standard IP Access List Configuration Commands

Standard IP Access List EXEC Commands

Standard Access List on R1 Stopping Bob from Reaching Server1

Standard IP ACL: Example 2
The criteria for the access lists are as follows:
X Sam is not allowed access to Bugs or Daffy.
X Hosts on the Seville Ethernet are not allowed access to hosts on the Yosemite Ethernet.
X All other combinations are allowed.

Network Diagram for Standard Access List Example

Yosemite Configuration for Standard Access List Example

Seville Configuration for Standard Access List Example

Yosemite Configuration for Standard Access List Example: Alternative Solution

Extended IP ACL Configuration
Extended IP Access List Configuration Commands

Extended IP Access List EXEC Commands

Extended IP Access Lists: Example 1
In this case, Bob is denied access to all FTP servers on R1’s Ethernet, and Larry is denied access to
Server1’s web server.

Network Diagram for Extended Access List Example 1

R1’s Extended Access List

R3’s Extended Access List Stopping Bob from Reaching FTP Servers Near R1

Extended IP Access Lists: Example 2
This example uses the same criteria and network topology as the second standard IP ACL example, as
repeated here:
X Sam is not allowed access to Bugs or Daffy.
X Hosts on the Seville Ethernet are not allowed access to hosts on the Yosemite Ethernet.
X All other combinations are allowed.

Network Diagram for Extended Access List

Yosemite Configuration for Extended Access List

Named Access List Configuration

Controlling Telnet Access with ACLs
vty Access Control Using the access-class Command

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