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Chapter 3      Basic Router Configuration
Configuring Dynamic Routing
Configuring Dynamic Routing
In dynamic routing, the network protocol adjusts the path automatically based on network traffic or 
topology. Changes in dynamic routing are shared with other routers in the network.
The IP routing protocol can use the Routing Information Protocol (RIP) or the Enhanced Interior 
Gateway Routing Protocol (IGRP) to learn routes dynamically. You can configure either one of these 
routing protocols.
Configuring RIP
To configure RIP routing protocol on the router, use the following table, beginning in global 
configuration mode.
For complete information on the dynamic routing commands, see the Cisco IOS Release 12.2 
documentation set. For more general information on RIP, see Chapter 1, “Concepts.” 
Configuration Example
The following configuration shows RIP version 2 enabled in IP network 10.10.10.0.
You do not need to enter the commands marked “default.” These commands appear automatically in the 
configuration file generated when you use the show running-config command.
!
router rip
version 2 
network 10.0.0.0
no auto-summary
!
Verifying Your Configuration
To verify that you have properly configured RIP, enter the show ip route command and look for RIP 
routes signified by “R.” You should see a verification output like the example shown below. 
router#show ip route
Codes:C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
Command Task
Step 1router ripEnter router configuration mode and enable RIP 
on the router.
Step 2version 2Specify use of RIP version 2.
Step 3network network-numberSpecify the network number for each directly 
connected network.
Step 4no auto-summaryDisable automatic summarization of subnet routes 
into network-level routes. This allows subprefix 
routing information to transmit across classful 
network boundries.
Step 5endExit router configuration mode. 
						

							  
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Chapter 3      Basic Router Configuration
Configuring IP Enhanced IGRP
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS
inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route
Gateway of last resort is not set
     2.0.0.0/24 is subnetted, 1 subnets
C  2.2.2.0 is directly connected, Ethernet0/0
R    3.0.0.0/8 [120/1] via 2.2.2.1, 00:00:02, Ethernet0/0
Configuring IP Enhanced IGRP
To configure IP Enhanced IGRP, use the following table, beginning in global configuration mode.
For complete information on the IP Enhanced IGRP commands, see the Cisco IOS Release 12.2 
documentation set. For more general information on Enhanced IGRP concepts, see Chapter 1, 
“Concepts.”
Configuration Example
The following configuration shows Enhanced IGRP routing protocol enabled in IP networks 10.0.0.0 and 
172.17.0.0. The Enhanced IGRP autonomous system number is assigned as 100.
You do not need to enter the commands marked “default.” These commands appear automatically in the 
configuration file generated when you use the show running-config command.
!
router eigrp 100
network 10.0.0.0
network 172.17.0.0
!
Command Purpose
Step 1router eigrp autonomous-systemEnters router configuration mode and enable 
Enhanced IGRP on the router. The 
autonomous-system number identifies the route 
to other Enhanced IGRP routers and is used to tag 
the Enhanced IGRP information.
Step 2network network-numberSpecifies the network number for each directly 
connected network.
Step 3endExits router configuration mode. 
						

							  
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Chapter 3      Basic Router Configuration
Configuring Addressing Parameters
Verifying Your Configuration
To verify that you have properly configured IP Enhanced IGRP, enter the show ip route command and 
look for Enhanced IGRP routes signified by “D.” You should see a verification output like the example 
shown below.
router#show ip route
Codes:C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route
Gateway of last resort is not set
2.0.0.0/24 is subnetted, 1 subnets
C  2.2.2.0 is directly connected, Ethernet0/0
D    3.0.0.0/8 [90/409600] via 2.2.2.1, 00:00:02, Ethernet0/0
Configuring Addressing Parameters
This section describes how to configure addressing using Network Address Translation (NAT) and Easy 
IP Phase 1 and 2.
Configuring NAT 
You can configure NAT for either static or dynamic address translations.
To configure static or dynamic inside source translation using NAT, use the following table, beginning 
in global configuration mode.
Command Purpose
Step 1ip nat pool name start-ip end-ip {netmask 
netmask | prefix-length prefix-length}Creates pool of global IP addresses for NAT. 
Step 2access-list access-list-number permit source 
[source-wildcard]Defines a standard access list permitting 
addresses that need translation.
Step 3ip nat inside source list access-list-number pool 
nameEnables dynamic translation of addresses 
permitted by access list to one of addresses 
specified in pool.
Step 4ip nat inside source static local-ip global-ip 
number extendableEnables static translation of specified inside local 
address to globally unique IP address. This 
command is optional.
Step 5interface ethernet 0Enters configuration mode for Ethernet interface.
Step 6ip nat insideEstablishes Ethernet interface as inside interface.
Step 7exitExits configuration mode for Ethernet interface.
Step 8interface atm 0Enters configuration mode for ATM interface. 
						

							  
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Chapter 3      Basic Router Configuration
Configuring Addressing Parameters
NoteIf you want to use NAT with a Virtual-Template interface, you must configure a loopback interface.
For complete information on the NAT commands, see the Cisco IOS Release 12.2 documentation set. 
For more general information on NAT concepts, see Chapter 1, “Concepts.”
Configuration Example
The following configuration shows NAT configured for the Ethernet and ATM interfaces.
The Ethernet 0 interface has an IP address of 192.168.1.1 with a subnet mask of 255.255.255.0. NAT is 
configured for inside, which means that the interface is connected to the inside network that is subject 
to NAT translation.
The ATM 0 interface has an IP address of 200.200.100.1 and a subnet mask of 255.255.255.0. NAT is 
configured for outside, which means that the interface is connected to an outside network, such as the 
Internet.
You do not need to enter the commands marked “default.” These commands appear automatically in the 
configuration file generated when you use the show running-config command.
!
interface Ethernet0
ip address 192.168.1.1 255.255.255.0
no ip directed-broadcast (default)
ip nat inside
!
interface ATM0
ip address 200.200.100.1 255.255.255.0
no ip directed-broadcast (default)
ip nat outside
no atm ilmi-keepalive (default)
pvc 8/35 
encapsulation aal5snap
!
ip route 0.0.0.0.0.0.0.0 200.200.100.254
!
ip nat pool test 200.200.100.1 200.200.100.1 netmask 255.255.255.0
ip nat inside source list 101 pool test overload
ip classless (default)
!
Step 9dsl equipment-type {co | cpe} Configures the DSL equipment type, if 
applicable.
Step 10dsl linerate {number | auto} Specifies the G.SHDSL line rate, if applicable. 
The range of valid numbers is between 72 and 
2312.
Step 11dsl operating-mode gshdsl symmetric annex 
annexSets the G.SHDSL operating mode, if applicable, 
and select the G.991.2 annex.
Step 12ip nat outsideEstablishes ATM interface as outside interface.
Step 13exitExits configuration mode for ATM interface. Command Purpose 
						

							  
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Chapter 3      Basic Router Configuration
Configuring Addressing Parameters
Verifying Your Configuration
To verify that you have properly configured NAT, enter the show ip nat statistics command. You should 
see a verification output like the example shown below.
router#show ip nat statistics 
Total active translations:45 (10 static, 35 dynamic; 45 extended)
Outside interfaces:
  ATM0
Inside interfaces:
  Ethernet0
Hits:34897598  Misses:44367
Expired translations:119305
Dynamic mappings:
-- Inside Source
access-list 1 pool homenet refcount 14
pool homenet:netmask 255.255.255.0
        start 200.200.100.1 end 200.200.100.1
        type generic, total addresses 1, allocated 1 (100%), misses 
Configuring Easy IP (Phase 1)
This section explains how to configure Easy IP (Phase 1). Easy IP Phase 1 includes NAT overload and 
PPP/Internet Protocol Control Protocol (IPCP). NAT overload means that you can use one registered IP 
address for the interface and use it to access the Internet from all devices in the network. 
With PPP/IPCP, Cisco 800-series routers automatically negotiate a globally unique (registered or public) 
IP address for the interface from the ISP route.
To configure Easy IP (Phase 1), use the following table, beginning in global configuration mode.
Command Purpose
Step 1access-list access-list-number permit source 
[source-wildcard] Defines a standard access list that permits 
nonregistered IP addresses of hosts.
Step 2ip nat inside source list access-list-number 
interface interface overloadSets up translation of addresses identified by the 
access list defined in Step 1.
Step 3interface ethernet 0Enters configuration mode for Ethernet interface.
Step 4ip nat insideEstablishes the Ethernet interface as inside 
interface for NAT.
Step 5no shutdownEnables the Ethernet interface and the 
configuration changes just made to it.
Step 6exitExits configuration mode for Ethernet interface.
Step 7interface dialer Enters configuration mode for the dialer interface. 
Step 8ip address negotiatedAssigns a negotiated IP address to the dialer 
interface.
Step 9ip nat outsideEstablishes the dialer interface as the outside 
interface for NAT.
Step 10dialer pool numberSpecifies which dialer pool number you are using.
Step 11exitExits the dialer interface.
Step 12interface ATM 0Enters configuration mode for the ATM interface. 
						

							  
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Chapter 3      Basic Router Configuration
Configuring Addressing Parameters
For complete information on the Easy IP commands, see the Cisco IOS Release 12.2 documentation set. 
For more general information on Easy IP (Phase 1) concepts, see Chapter 1, “Concepts.” 
Configuring Easy IP (Phase 2)
This section explains how to configure the Cisco 800 series routers as DHCP servers.
The Easy IP (Phase 2) feature combines DHCP server and relay. With DHCP, LAN devices on an IP 
network (DHCP clients) can request IP addresses from the DHCP server. The DHCP server allocates IP 
addresses from a central pool as needed. A DHCP server can be a workstation, PC, or a Cisco router. 
With the DHCP relay feature configured on the router, the routers can relay IP address requests from the 
LAN interface and to the DHCP server as shown in Figure 3-1.
Figure 3-1 Easy IP (Phase 2) – DHCP Server and Relay Step 13
dsl equipment-type {co | cpe} Configures the DSL equipment type, if 
applicable.
Step 14dsl linerate {number | auto} Specifies the G.SHDSL line rate, if applicable. 
The range of valid numbers is between 72 and 
2312.
Step 15dsl operating-mode gshdsl symmetric annex 
annexSets the G.SHDSL operating mode, if applicable, 
and select the G.991.2 annex.
Step 16pvc vpi/vciCreates an ATM PVC for each end node with 
which the router communicates.
Step 17encapsulation aal5mux ppp dialer Specifies the encapsulation type for the PVC to be 
AAL5MUX PPP and point back to the dialer 
interface. 
Step 18dialer pool-member numberSpecifies which dialer pool-member you are 
using.
Step 19no shutdownEnables the interface and configuration changes 
just made to the ATM interface.
Step 20exitExits configuration mode for the ATM interface. Command Purpose
1DHCP client4Corporate office
2Remote office5DHCP server
3DHCP relay
Cisco 827 Cisco 3600
AT M
74583
1
3
24
5 
						

							  
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Chapter 3      Basic Router Configuration
Configuring DHCP
Configuring DHCP
The following sections describe how to configure the router as a DHCP client, server, or relay.
Configuring DHCP Client Support
Follow these steps to configure the router for DHCP client support:
Step 1Configure the BVI interface by entering the ip address dhcp client-id Ethernet 0 command. 
Specifying the value client-id ethernet0 means that the MAC address of the Ethernet interface is used as 
the client ID when the DHCP request is sent. Otherwise, the MAC address of the BVI interface is used 
as the client ID.
Step 2Configure NAT:
a.Configure the BVI interface by entering the ip nat outside command.  
b.Configure the Ethernet interface by entering the ip nat inside command.
c.Create an access list under NAT by entering the access-list 1 permit ip address command to match 
all Ethernet IP addresses.
d.Configure the source list under NAT by entering the 
ip nat inside source list 1 interface BVI 1 overload command.
Step 3Configure the router to act as a DHCP server. This step is optional.
a.At the config-if router prompt, enter the ip dhcp pool server name command.
b.Enter the import all command to have the Cisco 827 router retrieve the Microsoft Windows 
nameserver (WINS) and domain name system (DNS) server addresses for name resolution.
Configuration Example
The following example shows a configuration of the DHCP client.
Current configuration:
!
version 12.2
no service pad
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname c827
!
!
ip subnet-zero
ip dhcp excluded-address 10.10.10.1
!
ip dhcp pool SERVER
network 10.10.10.0 255.255.255.0
default-router 10.10.10.1 
import all
! 
bridge irb 
						

							  
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Chapter 3      Basic Router Configuration
Configuring DHCP
interface Ethernet0
ip address 10.10.10.1 255.255.255.0
no ip directed-broadcast
ip nat inside
!
interface ATM0
no ip address
no ip directed-broadcast
no atm ilmi-keepalive
bundle-enable
hold-queue 208 in
!
interface ATM0.1 point-to-point
no ip directed-broadcast
pvc 1/100 
encapsulation aal5snap
!
bridge-group 1
!
interface ATM0.2 point-to-point
ip address 5.0.0.2 255.0.0.0
no ip directed-broadcast
pvc 1/101 
protocol ip 5.0.0.1 broadcast
protocol ip 5.0.0.5 broadcast
encapsulation aal5snap
!
!
interface BVI1
ip address dhcp client-id Ethernet0
no ip directed-broadcast
ip nat outside
!
ip nat inside source list 1 interface BVI1 overload
ip classless
ip route 0.0.0.0 0.0.0.0 BVI1
no ip http server
!
access-list 1 permit 10.10.10.0 0.0.0.255
bridge 1 protocol ieee
bridge 1 route ip
!
voice-port 1
timing hookflash-in 0
!
voice-port 2
timing hookflash-in 0
!
voice-port 3
timing hookflash-in 0
!
voice-port 4
timing hookflash-in 0
!
!
line con 0
exec-timeout 0 0
transport input none
stopbits 1
line vty 0 4
password lab
login     
						

							  
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Chapter 3      Basic Router Configuration
Configuring DHCP
!
scheduler max-task-time 5000
end
Configuring DHCP Server
To configure the router as a DHCP server, use the following table, beginning in global configuration 
mode.
For more information on the features not used in this configuration, see the Cisco IOS DHCP Server 
feature module. For more general information on DHCP servers, see Chapter 1, “Concepts.” 
Configuration Example
The following configuration shows a DHCP server configuration for the IP address 20.1.1.2.
!
ip dhcp pool CLIENT
   network 20.20.20.0 255.255.255.0
   domain-name cisco.com
   default-router 20.20.20.20
   netbios-name-server 1.1.1.1
   dns-server 1.1.1.2
   lease 0 1
!
Verifying Your Configuration
To verify that you have properly configured the DHCP server, enter the show dhcp server command and 
look for the assigned server IP. You should see a verification output like the example shown below.
router# show dhcp server 
show ip dhcp binding
show ip dhcp conflict
show ip dhcp server statics
Command Purpose
Step 1ip dhcp pool nameEnters DHCP configuration mode, and create a 
pool of IP addresses that can be assigned to DHCP 
clients.
Step 2network ip-address subnet-maskSpecifies a range of IP addresses that can be 
assigned to the DHCP clients.
Step 3domain-name domain nameConfigures the domain name.
Step 4dns-server ip-addressDesignates the router as the default router, and 
specify an IP address.
Step 5netbios-name-server ip-addressConfigures the netbios name server.
Step 6default-router ip-addressConfigures the DNS server.
Step 7lease days hours minutesSpecifies the duration of the lease.
Step 8exitExits DHCP configuration mode. 
						

							  
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Chapter 3      Basic Router Configuration
Configuring TACACS+
Configuring the DHCP Relay
This section describes how to configure the router to forward User Datagram Protocol (UDP) broadcasts, 
including IP address requests, from DHCP clients. 
To configure the DHCP relay, use the following table, beginning in global configuration mode.
For complete information on the DHCP relay commands, see the Cisco IOS Release 12.2 documentation 
set. For more general information on DHCP relays, see Chapter 1, “Concepts.” 
Configuration Example
The following configuration contains commands relevant to DHCP relay only. 
You do not need to enter the commands marked “default.” These commands appear automatically in the 
configuration file generated when you use the show running-config command.
!
int Ethernet0
ip address 192.168.100.1 255.255.255.0
ip helper-address 200.200.200.1
!
Verifying Your Configuration
To verify that you have properly configured the DHCP relay, enter the show dhcp server command. You 
should see a verification output like the example shown below. 
router#show dhcp server 
   DHCP server:2.2.2.2
    Leases:  0
    Offers:  0      Requests:0     Acks:0     Naks:0
Declines:0      Releases:0     Bad: 0
Configuring TACACS+
The Cisco 827, 831, 836, 837, 827H, and 827-4V routers and the Cisco SOHO 71, 91, 96, and 97 routers 
support the Terminal Access Controller Access Control System Plus (TACACS+) protocol through 
Telnet. TACACS+ is a Cisco proprietary authentication protocol that provides remote access 
authentication and related network security services, such as event logging. User passwords are Command Purpose
Step 1interface Ethernet 0Enters configuration mode for the Ethernet 
interface.
Step 2ip helper-address addressForwards default UDP broadcasts including IP 
configuration requests to the DHCP server.
Step 3no shutdownEnables the Ethernet interface and the 
configuration changes.
Step 4exitExits configuration mode for the Ethernet 
interface.