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Step 4If setting up a connection to a corporate network, you and the network 
administrator of the corporate network must decide on or generate the following 
information for the WAN interfaces of the routers so you can both use this 
information:
PPP authentication type: CHAP or PAP.
PPP client name to access the router.
PPP password to access the router.
Telephone number assigned to the telephone interface of your router.
Step 5If setting up IP routing, obtain the addressing scheme information for your IP 
network.
Connecting a Private IP Network to the Internet
In the network example shown in Figure 2-1 and Ta b l e 2 - 1, the Cisco 800 series 
router connects a private IP network to an ISP. 
Figure 2-1 Connecting Private IP Network to Internet
10.0.0.0 255.0.0.0
192.168.1.100
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Features Used
This network uses the following features on the LAN:
IP routing
Dynamic Host Configuration Protocol (DHCP) server (optional)
When your router is acting as a DHCP server, workstations configured as DHCP 
clients are automatically assigned an IP address and subnet mask. 
This network uses the following features on the WAN:
IP routing
PPP
Network Address Translation (NAT) overload
Internet Protocol Control Protocol (IPCP) 
CHAP or PAP over PPP
Dial-on-demand routing (DDR)
Static routes Callout 
Number Description
1DHCP server at Site 1
2National ISDN-1 switch type, with B1 SPID 40855511110101 and 
B2 SPID 40855522220101
3Private IP network
4DHCP client
5PPP link
6ISDN phone number, 4085551111
7Internet service provider
8CHAP or PAP
9Domain Name System (DNS) server 
						

							 
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With NAT overload configured, the router uses one address for multiple hosts. 
With IPCP configured, your router automatically negotiates its IP address from 
the router it is attempting to connect to.
You can use either CHAP or PAP as the PPP authentication protocol. Cisco 
recommends using CHAP, because it is the more secure of the two protocols.
In addition, the ISDN line is activated only when needed (DDR), using one route 
that has been manually configured (static route). DDR using static routes suits 
small networking environments that do not have complex routing topologies.
Configuration
To configure the features for this network example, perform the following steps 
on the PC, starting in global configuration mode.
Step 1Specify a name for the router. For example, specify SanJose as the router name:
router(config)# hostname SanJose
Step 2Specify an encrypted password containing from 1 to 25 uppercase or lowercase 
alphanumeric characters. Spaces are also valid password characters. Leading 
spaces are ignored; trailing spaces are recognized. For example, specify abra 
cadabra as the password:
SanJose(config)# enable secret abra cadabra
Step 3Configure the router to recognize the zero subnet range as a valid range of 
addresses:
SanJose(config)# ip subnet-zero
Step 4Disable the router from translating unfamiliar words entered during a console 
session into IP addresses:
SanJose(config)# no ip domain-lookup
Step 5Optional. Configure your router as a DHCP server. Define the DHCP relay pool 
name. For example:
router(config)# ip dhcp pool DHCPpoolLAN_0
a.Set the DHCP pool of addresses. For example:
router(dhcp-config)# network 10.0.0.0 255.255.255.0 
						

							 
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b.Set the IP addresses of the DNS servers. For example:
router(dhcp-config)# dns-server 192.168.1.100
c.Set the NetBIOS servers. For example:
router(dhcp-config)# netbios-name-server
10.1.1.2 10.1.1.3
d.Set the Ethernet 0 IP address as the default gateway. For example:
router(dhcp-config)# default-router 10.0.0.1
e.Exit to global configuration mode:
router(dhcp-config)# exit
Step 6Configure the LAN interface by performing the following steps:
a.Specify parameters for the LAN interface:
SanJose(config)# interface ethernet0
b.Set the IP address and subnet mask for the LAN interface. For example:
SanJose(config-if)# ip address 10.0.0.1 255.0.0.0
c.Activate the LAN interface:
SanJose(config-if)# no shutdown
Step 7Enable NAT on your LAN. The inside network address is not directly routed to 
the Internet, but is subject to translation to a routable address outside the LAN. 
For example:
SanJose(config-if)# ip nat inside
Step 8Configure the WAN interface by performing the following steps:
a.Change to global configuration mode:
SanJose(config-if)# exit
SanJose(config)#
b.Specify parameters for the WAN interface:
SanJose(config)# interface bri0
c.Enable PPP:
SanJose(config-if)# encapsulation ppp 
						

							 
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d.Enable multilink PPP:
SanJose(config-if)# ppp multilink
e.Enable the translation of the inside network to a valid Internet address:
SanJose(config-if)# ip nat outside
f.Create a dialer rotary group, specifying a number between 0 and 255. Dialer 
rotary groups are useful in environments that require multiple calling 
destinations. For example:
SanJose(config-if)# dialer rotary-group 0
g.North America only. Associate the ISDN local directory numbers (LDNs) 
provided by your telephone service provider with the first and second SPIDs. 
You can specify the SPID number, or you can have it automatically detected 
by entering a 0.
In the following example, the SPID number is represented by a 0, so that it 
will be automatically detected. The primary LDN is followed by the 
secondary LDN for each SPID.
SanJose(config-if)# isdn spid1 0 4085551111 4085552222
SanJose(config-if)# isdn spid2 0 4085553333 4085554444
NoteFind out from your telephone service provider whether you need to 
specify an area code for the LDN.
h.North America only. If you had manually entered the SPID number, enable 
the BRI0 interface.
SanJose(config-if)# no shutdown
i.North America only. If you configured the SPID to be automatically detected, 
enable the automatic detection of ISDN SPID numbers and switch type:
SanJose(config-if)# isdn autodetect
j.Outside of North America only. Specify the ISDN switch type. To get a 
listing of supported switches, enter the isdn switch-type ? command.
The following example specifies the NET3 switch type:
router(config-if)# isdn switch-type basic-net3 
						

							 
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k.Disable the Cisco Discovery Protocol (CDP):
SanJose(config-if)# no cdp enable
Step 9Follow these steps to specify characteristics of the dialer rotary group that were 
created in the previous step:
a.Change to global configuration mode:
SanJose(config-if)# exit
SanJose(config)#
b.Create a dialer interface, specifying a number between 0 to 255 to represent 
your dialer rotary group. For example:
SanJose(config)# interface dialer 0
SanJose(config-if)#
c.Specify that the IP address for this interface is obtained by using IPCP:
SanJose(config-if)# ip address negotiated
d.Enable PPP as the encapsulation type:
SanJose(config-if)# encapsulation ppp
e.Enable DDR:
SanJose(config-if)# dialer in-band
f.Specify the amount of time in number of seconds that the line can be idle 
before it is disconnected:
SanJose(config-if)# dialer idle-timeout 300
g.Specify the telephone number of the interface to be called if you are calling 
a single site. For example:
SanJose(config-if)# dialer string 14085553333
h.Set the maximum number of packets to be held in the outgoing queue to 10. 
If an ISDN connection does not exist yet, the hold queue holds up to 10 
packets before dropping them. For example:
SanJose(config-if)# dialer hold-queue 10 
						

							 
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i.Define the load level that must be exceeded on the first ISDN B channel 
before the second B channel is brought up. The load-threshold variable 
represents a utilization percentage and is a number between 1 and 255, where 
255 equals 100 percent. For example:
SanJose(config-if)# dialer load-threshold 10 outbound
NoteEnter outbound to calculate the load using outbound data only, 
inbound to calculate the load using inbound data only, and either to 
set the maximum calculated load as the larger of the outbound and 
inbound loads.
j.Assign this interface to dialer access group 1:
SanJose(config-if)# dialer-group 1
k.Configure CHAP, then specify a CHAP host name and password. To 
configure PAP, skip this step and go to the next step.
This command enables CHAP and specifies authentication on incoming calls 
only. Unidirectional authentication is used because non-Cisco routers that do 
not support bidirectional authentication are potentially in use at the ISP. In 
these cases, when the SanJose router calls the ISP, SanJose does not 
authenticate. However, the ISP authenticates SanJose before allowing the 
connection. 
SanJose(config-if)# ppp authentication chap callin
router(config-if)# ppp chap hostname SanJose
router(config-if)# ppp chap password gocisco1
l.Configure PAP. To configure CHAP, skip this step and follow the previous 
step. 
The following command enables PAP and specifies authentication on 
incoming calls only. Unidirectional authentication is used because routers 
that do not support bidirectional authentication are potentially in use at the 
ISP. In these cases, when the SanJose router calls the ISP, SanJose does not 
authenticate. However, the ISP authenticates SanJose before allowing the 
connection. 
SanJose(config-if)# ppp authentication pap callin 
						

							 
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m.Enable remote PAP support for an interface. The username and password are 
sent in the PAP authentication request packet. The password must contain 
from 1 to 25 upper- and lowercase alphanumeric characters; it cannot contain 
spaces nor underscores. 
SanJose(config-if)# ppp pap sent-username SanJose
password gocisco
n.Enable multilink PPP:
SanJose(config-if)# ppp multilink
Step 10Follow these steps to configure how the IP routing protocol learns routes:
a.Change to global configuration mode:
SanJose(config-if)# exit
SanJose(config)#
b.Set up all IP addresses to be treated as classless:
SanJose(config)# ip classless
c.Enable IP routing and set up a static route. Typically, the ISP does not provide 
IP addresses and subnet masks of their networks, but they do provide the IP 
address of the ISDN router interface to which your router is connected.
The following example specifies that you need to use dialer 0 on your router 
to reach the ISP router. Dialer 0 had been previously configured using the 
interface dialer command.
SanJose(config)# ip routing
SanJose(config)# ip route 0.0.0.0 0.0.0.0 192.168.1.1
SanJOse(config)# ip route 192.168.1.1 255.255.255.255 dialer0
Step 11Specify that dialer-list 1 permits dialing by the IP routing protocol:
SanJose(config)# dialer-list 1 protocol ip permit
Step 12Perform this step only if ISDN calls at 64 kbps are not supported. Specify 
characteristics of the outgoing calls from an ISDN interface by using the 
following steps:
a.Define a class of shared configuration parameters for outgoing calls from an 
ISDN interface:
SanJose(config)# map-class dialer 56k
The unique identifier that identifies the class is 56k. 
						

							 
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b.Specify 56 kbps as the B channel speed:
SanJose(config-map-class)# dialer isdn speed 56
Step 13If you have a Cisco 800 series router that is connected to a telephone, fax machine, 
or modem, configure the telephone interfaces by performing the following steps:
a.Change to global configuration mode:
SanJose(config-map-class)# exit
SanJose(config)#
b.Specify the country where your router is located:
SanJose(config)# pots country us
Enter the pots country ? command to get a list of supported countries and 
codes.
This command determines the physical characteristics of the telephone 
interfaces. By specifying a country, you are configuring your telephone to use 
country-specific default settings for each of the physical characteristics.
c.Create dial peers to determine how incoming calls are routed to the telephone 
ports. In the following example, the dial-peer tag is 1, the ISDN local 
directory number LDN is 5551111, the telephone port is 1, and call waiting 
is disabled:
SanJose(config)# dial-peer voice 1 pots
SanJose(config-dial-peer)# destination-pattern 5551111
SanJose(config-dial-peer)# port 1
SanJose(config-dial-peer)# no call-waiting
SanJose(config-dial-peer)# exit
SanJose(config)#
NoteEnter a number between 1 and 6 for the dial-peer tag variable. 
Find out from your telephone service provider whether or not you 
need to specify an area code for the LDN.
d.Specify parameters for the WAN interface:
SanJose(config)# interface bri0 
						

							 
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e.Specify that incoming voice calls shall be forwarded to the devices connected 
to the telephone ports:
SanJose(config-if)# isdn incoming-voice modem
Step 14Exit the interface configuration mode.
SanJose(config-if)# exit
SanJose#(config)#
Step 15In global configuration mode, set global NAT commands. In the following 
example, all inside network addresses assigned to interface BRI0 are configured 
for translation, and the access list that contains the inside network addresses is 
defined.
SanJose(config)# ip nat inside source list 1 interface bri0
overload
SanJose(config)# access-list 1 permit 10.0.0.0 255.0.0.0
Step 16Change to user mode and save your configuration:
SanJose(config)# exit
SanJose# copy running-config startup-config
Connecting a Public IP Network to the Internet
In the network example shown in Figure 2-2 and Ta b l e 2 - 2, the Cisco 800 series 
router connects a public IP network to an ISP. The ISP has assigned a range of 
registered (public) IP addresses for the LAN devices that require Internet access.