Configure an Interface to Acquire a Dynamic IP Address

In this example, switch 1 is the DHCP server, and switch 2 is the DHCP client. vlan1 of switch 2 must be allocated with a dynamic IP. In addition, the address pool is pool 1, the network address is 12.0.0.0, and the mask option is 255.255.0.0.

1. Enable the DHCP server in switch 1.

   SEFOS# configure terminal
   SEFOS(config)# service dhcp-server
   

2. Create the address pool.

   SEFOS(config)# ip dhcp pool 1
   

3. Configure the network and mask.

   SEFOS(dhcp-config)# network 12.0.0.0 255.0.0.0
   SEFOS(dhcp-config)# end
   

4. View the configuration.

   SEFOS# show ip dhcp server pools
   Pool Id                             : 1
   -------------------------------------------
   Subnet                               : 12.0.0.0
   Subnet Mask                          : 255.0.0.0
   Lease time                          : 3600 secs
   Utilization threshold               : 75%
   Start Ip                            : 12.0.0.1
   End Ip                              : 12.255.255.255
    
   Subnet Options
   --------------
   Code        :    1, Value      : 255.255.0.0
   

5. View additional configuration details.

   Note that DHCP does not cross the subnet.

   SEFOS# show ip dhcp server information
    
   DHCP server status                  : Enable
   Send Ping Packets                   : Disable
   Debug level                         : None
   Server Address Reuse Timeout        : 5 secs
   Next Server Address                 : 0.0.0.0
   Boot file name                      : NULL
   

6. Instead of using port 1 as shown in the topologies presented in this guide, use port 41 of both switches as follows. The DHCP server must be enabled and there must be a pool available in the server for the client's subnet.
   1. Connect a cable between port 41 of switch 1 and 2.
   2. Activate interface 41.

      SEFOS# configure terminal
      SEFOS(config)# interface ex 0/41
      SEFOS(config-if)# no shutdown
      SEFOS(config-if)# exit
      

   3. Define a VLAN using port 41.

      SEFOS(config)# vlan 41
      SEFOS(config-vlan)# port ex 0/41
      SEFOS(config-vlan)# exit
      

   4. Assign IP 12.0.0.1 to vlan 41.

      SEFOS(config)# interface vlan 41
      SEFOS(config-if)# no shutdown
      SEFOS(config-if)# ip address 12.0.0.1 255.255.255.0
      SEFOS(config-if)# end
      SEFOS# 
      

7. Execute the following commands in switch 2 to acquire a dynamic IP for vlan1 (note that DHCP does not cross the subnet).
   1. Activate interface 41.

      SEFOS# configure terminal
      SEFOS(config)# interface ex 0/41
      SEFOS(config-if)# no shutdown
      SEFOS(config-if)# exit
      

   2. Create the same VLAN.

      SEFOS(config)# vlan 41
      SEFOS(config-vlan)# port ex 0/41
      SEFOS(config-vlan)# exit
      

   3. Change the IP allocation mode to dynamic.

      SEFOS(config)# interface vlan 41
      SEFOS(config-if)# no shutdown
      SEFOS(config-if)# ip address dhcp
      SEFOS(config-if)# end
      SEFOS#
      

   4. Wait for the protocol operation to complete (approximately 20 seconds).
   5. View the dynamic IP allocated to the client in switch 2.

      SEFOS# show ip interface
      

      The output in the switch 2 is:

      vlan41 is up, line protocol is up
      Internet Address is 12.0.0.2/8
      Broadcast Address  12.255.255.255
      IP address allocation method is dynamic
      IP address allocation protocol is dhcp
      

   6. View the DHCP server binding table to observe the allocated IP addresses in switch 1.

      SEFOS# show ip dhcp server binding
       
      Ip          Hw                Hw               Binding       Expire
      Address     Type            Address            State         Time
      ---------   -------    ---------------        ----------    ----------
      12.0.0.2    Ethernet    00:02:02:03:04:01      Assigned       Jan 7  11:22:37 2007
      

   7. View the DHCP packets statistics in switch 1.

      SEFOS# show ip dhcp server statistics
       
      Address pools : 1
       
      Message             Received
      -------             --------
      DHCPDISCOVER         1
      DHCPREQUEST          1
      DHCPDECLINE          0
      DHCPRELEASE          0
      DHCPINFORM           0
       
      Message              Sent
      -------              ----
      DHCPOFFER            1
      DHCPACK              1
      DHCPNAK              0