Jaycee's Networking

December 15, 2008

DHCP configuration

Filed under: DHCP, IOS — Tags: — Jaycee @ 11:01 am

1. Excluding IP Address:

Router(config)# ip dhcp excluded-address low-address [high-address]
The IP addresses that the DHCP Server should not assign to DHCP clients.

2.Configuring a DHCP Address Pool:

Router(config)# ip dhcp pool name
Creates a name for the DHCP Server address pool and places you in DHCP pool configuration mode.

3. Configuring the DHCP Address Pool Subnet and Mask:

Router(dhcp-config)# network network-number [mask | /prefix-length]
Specifies the subnet network number and mask of the DHCP address pool.

4. Configuring the Domain Name:

Router(dhcp-config)# domain-name domain
Specifies the domain name for the client.

5. Configuring the IP Domain Name System Servers:

Router(dhcp-config)# dns-server address [address2 address8]
Specifies the IP address of DNS server(s).

6. Configuring the NetBIOS Windows Internet Naming Service (WINS) Servers:

Router(dhcp-config)# netbios-name-server address [address2 address8]
Specifies the NetBIOS WINS server that is available to Microsoft DHCP clients. WINS is a name resolution service that Microsoft DHCP clients use to correlate host names to IP addresses within a general grouping of networks.

7. Configuring the NetBIOS Node Type:

Router(dhcp-config)# netbios-node-type type
The NetBIOS node type can be one of four settings: broadcast, peer-to-peer, mixed, or hybrid.
b-node  Broadcast node
h-node  Hybrid node
m-node  Mixed node
p-node  Peer-to-peer node

8. Configuring the default router:

Router(dhcp-config)# default-router address [address2 address8]

9. Configuring that Address Lease Time:

Router(dhcp-config)# lease {days [hours][minutes] | infinite}
The default is a one-day lease. Use show ip dhcp binding to display the lease expiration time and date of the IP address of the host. An address binding is a mapping between the IP address and MAC address of a client.

10. Configuring DHCP Option for Lightweight Access Points

Router(dhcp-config)# option 60 ascii “VCI string”
Router(dhcp-config)# option 43 hex <hex string>

(1) For VCI Strings, check the table at: http://www.cisco.com/univercd/cc/td/doc/product/wireless/airo1130/1130hig5/113h_g.htm#wp1008197

(2) The hex string is assembled by concatenating the TLC values: Type + Length + Value

a. Type is always f1.

b. Length is the number of controller management IP addresses times 4 in hex.

c. Value is the IP address of the controller listed sequentially in hex.

d. For example, suppose there are 2 controllers with management interface IP addresses: and The length is 2*4 = 8 = 08 (hex). The IP addresses translate to 0a7e7e02 and 0a7f7f02. Assembling the string then yields f1080a7e7e020a7f7f02.

11. Example as below:

ip dhcp excluded-address
ip dhcp pool USER_NET
domain-name jayceechou.com
netbios-node-type b-node
option 43 hex f104.0a05.022a
option 60 ascii “Cisco AP c1130”
lease 30

12. Notes:

When changing DNS server statement, make sure it’s on the top of NETBIOS server statement; otherwise, all machine would ignore the changes and they are not going to get the correct DNS servers.


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