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Chapter 4      Configuring PPP over ATM with NAT
  Configuration Example
NoteIf you want to use NAT with a virtual-template interface, you must configure a loopback interface. See 
Chapter 1, “Basic Router Configuration,” for information on configuring the loopback interface.
For complete information on NAT commands, see the Cisco IOS Release 12.3 documentation set. For 
more general information on NAT concepts, see 
Appendix B, “Concepts.”
Configuration Example
The following configuration example shows a portion of the configuration file for a client in the PPPoA 
scenario described in this chapter.
The VLAN interface has an IP address of 192.168.1.1 with a subnet mask of 255.255.255.0. NAT is 
configured for inside and outside.
NoteCommands marked by “(default)” are generated automatically when you run the show running-config 
command.
!
interface Vlan1
 ip address 192.168.1.1 255.255.255.0 ip nat inside
 ip virtual-reassembly (default)
!interface ATM0
 no ip address
 ip nat outside ip virtual-reassembly
 no atm ilmi-keepalive
 pvc 8/35  encapsulation aal5mux ppp dialer
  dialer pool-member 1
 ! dsl operating-mode auto
!
Step 10exit
Example:
Router(config-if)# exitRouter(config)# 
Exits configuration mode for the ATM interface.
Step 11access-list access-list-number {deny | permit} 
source [source-wildcard]
Example:
Router(config)# access-list 1 permit 
192.168.1.0 0.0.0.255
Defines a standard access list permitting addresses 
that need translation.
NoteAll other addresses are implicitly denied.
Command Purpose 
						

							 
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  Configuration Example
interface Dialer0 ip address negotiated
 ip mtu 1492
 encapsulation ppp dialer pool 1
 dialer-group 1
 ppp authentication chap!
ip classless (default)
!ip nat pool pool1 192.168.1.0 192.168.2.0 netmask 0.0.0.255
ip nat inside source list 1 interface Dialer0 overload
!access-list 1 permit 192.168.1.0 0.0.0.255
dialer-list 1 protocol ip permit
ip route 10.10.25.2 0.255.255.255 dialer 0
!
Verifying Your Configuration
Use the show ip nat statistics command in privileged EXEC mode to verify the PPPoA client with NAT 
configuration. You should see verification output similar to the following example:
Router# show ip nat statistics
Total active translations: 0 (0 static, 0 dynamic; 0 extended)Outside interfaces:
  ATM0
Inside interfaces:  Vlan1
Hits: 0  Misses: 0
CEF Translated packets: 0, CEF Punted packets: 0Expired translations: 0
Dynamic mappings:
-- Inside Source[Id: 1] access-list 1 interface Dialer0 refcount 0
Queued Packets: 0 
						

							
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5
Configuring a LAN with DHCP and VLANs
The Cisco 870 series routers support clients on both physical LANs and virtual LANs (VLANs). The 
routers can use the Dynamic Host Configuration Protoc ol (DHCP) to enable automatic assignment of IP 
configurations for nodes on these networks.
Figure 5-1  shows a typical deployment scenario with tw o physical LANs connected by the router and 
two VLANs. 
Figure 5-1 Physical and Virtual LANs with DHCP Configured on the Cisco Router
92339
1
2
3
4
1Fast Ethernet LAN (with multiple networked devices)
2Router and DHCP server—Cisco 870 series  access router—connected to the Internet
3VLAN 1
4VLAN 2
DHCP
DHCP, which is described in RFC 2131, uses a cl ient/server model for address allocation. As an 
administrator, you can configure your Cisco
 800 series router to act as  a DHCP server, providing IP 
address assignment and other TCP/IP-oriented configuration information to your workstations. DHCP 
frees you from having to manually assign an IP address to each client. 
						

							 
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Chapter 5      Configuring a LAN with DHCP and VLANs
  Configure DHCP
When you configure a DHCP server, you must configure the server properties, policies, and DHCP 
options. 
NoteWhenever you change server properties, you must reload the server with the configuration data from the 
Network Registrar database.
VLANs
The Cisco 870 series access routers support four Fast Ethernet ports on which you can configure 
VLANs.
VLANs enable networks to be segmented and formed into logical groups of users, regardless of the 
user’s physical location or LAN connection.
Configuration Tasks
Perform the following tasks to configure this network scenario:
 Configure DHCP
 Configure VLANs
NoteThe procedures in this chapter assume you have already configured basic router features as well as 
PPPoE or PPPoA with NAT. If you have not performed these configurations tasks, see 
Chapter 1, “Basic 
Router Configuration,” Chapter 3, “Configuring PPP over Ethernet with NAT,” and Chapter 4, 
“Configuring PPP over ATM with NAT” as appropriate for your router.
Configure DHCP
Perform these steps to configure your router for DHCP operation, beginning in global configuration 
mode:
CommandPurpose
Step 1ip domain name name
Example:
Router(config)# ip domain name smallbiz.com
Router(config)# 
Identifies the default domain that the router uses to 
complete unqualified hostnames (names without a 
dotted-decimal domain name).
Step 2ip name-server server-address1 
[server-address2...server-address6]
Example:
Router(config)# ip name-server 192.168.11.12Router(config)# 
Specifies the address of one or more Domain Name 
System (DNS) servers to use for name and address 
resolution. 
						

							 
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  Configure DHCP
Step 3ip dhcp excluded-address low-address 
[high-address] 
Example:
Router(config)# ip dhcp excluded-address 
192.168.9.0
Specifies IP addresses that the DHCP server should 
not assign to DHCP clients. In this example, we are 
excluding the router address.
Step 4ip dhcp pool name
Example:
Router(config)# ip dhcp pool dpool1
Router(config-dhcp)# 
Creates a DHCP address pool on the router and 
enters DHCP pool configuration mode. The name 
argument can be a string or an integer.
Step 5network network-number [mask | prefix-length]
Example:
Router(config-dhcp)# network 10.10.0.0 
255.255.255.0
Router(config-dhcp)# 
Defines subnet number (IP) address for the DHCP 
address pool, optionally including the mask. 
Step 6import all
Example:
Router(config-dhcp)# import allRouter(config-dhcp)# 
Imports DHCP option parameters into the DHCP 
portion of the router database.
Step 7default-router address [address2...address8]
Example:
Router(config-dhcp)# default-router 
10.10.10.10
Router(config-dhcp)# 
Specifies up to 8 default routers for a DHCP client.
Step 8dns-server address [address2...address8]
Example:
Router(config-dhcp)# dns-server 192.168.35.2
Router(config-dhcp)# 
Specifies up to 8 DNS servers available to a DHCP 
client.
Command Purpose 
						

							 
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Chapter 5      Configuring a LAN with DHCP and VLANs
  Configure DHCP
Configuration Example
The following configuration example shows a portion of the configuration file for the DCHP 
configuration described in this chapter.
ip dhcp excluded-address 192.168.9.0
!ip dhcp pool dpool1
   import all
   network 10.10.0.0 255.255.255.0   default-router 10.10.10.10
   dns-server 192.168.35.2
   domain-name cisco.com!
ip domain name smallbiz.com
ip name-server 192.168.11.12
Verify Your DHCP Configuration
Use the following commands to view your DHCP configuration.
 show ip dhcp import—Displays the optional parameters imported into the DHCP server database.
 show ip dhcp pool—Displays information about the DHCP address pools.
 show ip dhcp server statistics—Displays the DHCP server statistics, such as the number of address 
pools, bindings, and so forth.
Router# show ip dhcp import
Address Pool Name: dpool1
Router# show ip dhcp pool
Pool dpool1 : Utilization mark (high/low)    : 100 / 0
 Subnet size (first/next)       : 0 / 0
 Total addresses                : 254 Leased addresses               : 0
 Pending event                  : none
 1 subnet is currently in the pool : Current index        IP address range                    Leased addresses
 10.10.0.1            10.10.0.1        - 10.10.0.254       0
Step 9domain-name domain
Example:
Router(config-dhcp)# domain-name cisco.comRouter(config-dhcp)# 
Specifies the domain name for a DHCP client.
Step 10exit
Example:
Router(config-dhcp)# exit
Router(config)# 
Exits DHCP configuration mode, and enters global 
configuration mode.
Command Purpose 
						

							
 
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Router# show ip dhcp server statistics
Memory usage         15419
Address pools        1Database agents      0
Automatic bindings   0
Manual bindings      0Expired bindings     0
Malformed messages   0
Secure arp entries   0
Message              Received
BOOTREQUEST          0DHCPDISCOVER         0
DHCPREQUEST          0
DHCPDECLINE          0DHCPRELEASE          0
DHCPINFORM           0
Message              Sent
BOOTREPLY            0
DHCPOFFER            0DHCPACK              0
DHCPNAK              0
Router#
Configure VLANs
Perform these steps to configure VLANs on your router, beginning in privileged EXEC mode:
CommandPurpose
Step 1vlan database
Example:
Router# vlan database
Router(vlan)# 
Enters VLAN configuration mode.
Step 2vlan vlan-id  [media  type] [name  vlan-name ]
Example:
Router(vlan)#  vlan 2 media ethernet name 
VLAN0002
Router(vlan)#  vlan 3 media ethernet name 
red-vlan
Router(vlan)# 
Adds VLANs, with identifiers ranging from 2 to 1001.
For details about this command and additional 
parameters that can be set, see the 
Cisco IOS 
Switching Services Command Reference.
Step 3exit
Example:
Router(vlan)#  exitRouter# 
Updates the VLAN database, propagates it throughout 
the administrative domain, and returns to privileged 
EXEC mode. 
						

							 
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  Configure VLANs
Verify Your VLAN Configuration
Use the following commands to view your VLAN configuration.
 show—Entered from VLAN database mode. Displays summary configuration information for all 
configured VLANs.
 show vlan-switch—Entered from privileged EXEC mode. Displays detailed configuration 
information for all configured VLANs. 
						

							 
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  Configure VLANs
Router# vlan databaseRouter(vlan)# show
  VLAN ISL Id: 1
    Name: default    Media Type: Ethernet
    VLAN 802.10 Id: 100001
    State: Operational    MTU: 1500
    Translational Bridged VLAN: 1002
    Translational Bridged VLAN: 1003
  VLAN ISL Id: 1002
    Name: fddi-default    Media Type: FDDI
    VLAN 802.10 Id: 101002
    State: Operational    MTU: 1500
    Bridge Type: SRB
    Translational Bridged VLAN: 1    Translational Bridged VLAN: 1003
  VLAN ISL Id: 1003    Name: token-ring-default
    Media Type: Token Ring
    VLAN 802.10 Id: 101003
    State: Operational    MTU: 1500
    Bridge Type: SRB
    Ring Number: 0    Bridge Number: 1
    Parent VLAN: 1005
    Maximum ARE Hop Count: 7    Maximum STE Hop Count: 7
    Backup CRF Mode: Disabled
    Translational Bridged VLAN: 1    Translational Bridged VLAN: 1002
  VLAN ISL Id: 1004    Name: fddinet-default
    Media Type: FDDI Net
    VLAN 802.10 Id: 101004    State: Operational
    MTU: 1500
    Bridge Type: SRB    Bridge Number: 1
    STP Type: IBM
  VLAN ISL Id: 1005
    Name: trnet-default
    Media Type: Token Ring Net    VLAN 802.10 Id: 101005
    State: Operational
    MTU: 1500    Bridge Type: SRB
    Bridge Number: 1
    STP Type: IBM 
						

							 
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  Configure VLANs
Router# show vlan-switch
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------1    default                          active    Fa0, Fa1, Fa2, Fa3
1002 fddi-default                     active
1003 token-ring-default               active1004 fddinet-default                  active
1005 trnet-default                    active
VLAN Type  SAID       MTU   Parent RingNo BridgeNo Stp  BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1    enet  100001     1500  -      -      -        -    -        1002   10031002 fddi  101002     1500  -      -      -        -    -        1      1003
1003 tr    101003     1500  1005   0      -        -    srb      1      1002
1004 fdnet 101004     1500  -      -      1        ibm  -        0      01005 trnet 101005     1500  -      -      1        ibm  -        0      0
Router#