The Cisco 870 series routers support clients on both physical LANs and virtual LANs (VLANs). The routers can use the Dynamic Host Configuration Protocol (DHCP) to enable automatic assignment of IP configurations for nodes on these networks.
Figure 5-1 shows a typical deployment scenario with two physical LANs connected by the router and two VLANs.
Figure 5-1 Physical and Virtual LANs with DHCP Configured on the Cisco Router
1
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Fast Ethernet LAN (with multiple networked devices)
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2
|
Router and DHCP server—Cisco 870 series access router—connected to the Internet
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3
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VLAN 1
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4
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VLAN 2
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DHCP
DHCP, which is described in RFC 2131, uses a client/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.
When you configure a DHCP server, you must configure the server properties, policies, and DHCP options.
Note 
Whenever you change server properties, you must reload the server with the configuration data from the Network Registrar database.
Whenever 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:
Note The 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.
The 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:
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 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 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.
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
Router# show ip dhcp server statistics
Memory usage 15419
Address pools 1
Database agents 0
Automatic bindings 0
Manual bindings 0
Expired bindings 0
Malformed messages 0
Secure arp entries 0
Message Received
BOOTREQUEST 0
DHCPDISCOVER 0
DHCPREQUEST 0
DHCPDECLINE 0
DHCPRELEASE 0
DHCPINFORM 0
Message Sent
BOOTREPLY 0
DHCPOFFER 0
DHCPACK 0
DHCPNAK 0
Router#
Configure VLANs
Perform these steps to configure VLANs on your router, beginning in global configuration mode:
Command
|
Purpose
| |
|---|---|---|
Step 1
|
vlan ?
Example:
Router# config t
Router(config)#vlan ?
WORD ISL VLAN IDs 1-4094 accounting VLAN accounting configuration ifdescr VLAN subinterface ifDescr Router(config)#
|
Enters VLAN configuration mode.
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Step 2
|
ISL VLAN ID
Example:
Router(config)#
Router(config-
|
Adds VLANs, with identifiers ranging from
1- 4094.
For details about this command and additional parameters that can be set, see the Cisco IOS Switching Services Command Reference.
|
Step 3
|
exit
Example:
Router(config-
Router(config)# |
Updates the VLAN database, propagates it throughout the administrative domain, and returns to global configuration mode.
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Assign a Switch Port to a VLAN
Perform these steps to assign a switch port to a VLAN, beginning in global configuration mode:
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—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.
show vlan-switch—Entered from privileged EXEC mode. Displays detailed configuration information for all configured VLANs.Router# vlan database
Router(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: 2 Name: VLAN0002 Media Type: Ethernet VLAN 802.10 Id: 100002 State: Operational MTU: 1500
VLAN ISL Id: 3 Name: red-vlan Media Type: Ethernet VLAN 802.10 Id: 100003 State: Operational MTU: 1500
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
Router# show vlan-switch
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0, Fa1, Fa3
2 VLAN0002 active Fa2
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2
---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------
1 enet 100001 1500 - - - - - 1002 1003
2 enet 100002 1500 - - - - - 0 0
1002 fddi 101002 1500 - - - - - 1 1003
1003 tr 101003 1500 1005 0 - - srb 1 1002
1004 fdnet 101004 1500 - - 1 ibm - 0 0
1005 trnet 101005 1500 - - 1 ibm - 0 0
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