Example: Configuring DHCP client
Network configuration
As shown in Figure 30, on a LAN, Switch B contacts the DHCP server through VLAN-interface 2 to obtain an IP address, a DNS server address, and static route information. The DHCP client's IP address resides on subnet 10.1.1.0/24. The DNS server address is 20.1.1.1. The next hop of the static route to subnet 20.1.1.0/24 is 10.1.1.2.
The DHCP server uses Option 121 to assign static route information to DHCP clients. Figure 29 shows the Option 121 format. The destination descriptor field contains the following parts: subnet mask length and destination network address, both in hexadecimal notation. In this example, the destination descriptor is 18 14 01 01 (the subnet mask length is 24 and the network address is 20.1.1.0 in dotted decimal notation). The next hop address is 0A 01 01 02 (10.1.1.2 in dotted decimal notation).
Figure 29: Option 121 format
Figure 30: Network diagram
Procedure
IMPORTANT: By default, interfaces on the device are disabled (in ADM or Administratively Down state). To have an interface operate, you must use the undo shutdown command to enable that interface. | ||
Configure Switch A:
# Specify an IP address for VLAN-interface 2.
<SwitchA> system-view [SwitchA] interface vlan-interface 2 [SwitchA-Vlan-interface2] ip address 10.1.1.1 24 [SwitchA-Vlan-interface2] quit
# Exclude an IP address from dynamic allocation.
[SwitchA] dhcp server forbidden-ip 10.1.1.2
# Configure DHCP address pool 0. Specify the subnet, lease duration, DNS server address, and a static route to subnet 20.1.1.0/24.
[SwitchA] dhcp server ip-pool 0 [SwitchA-dhcp-pool-0] network 10.1.1.0 mask 255.255.255.0 [SwitchA-dhcp-pool-0] expired day 10 [SwitchA-dhcp-pool-0] dns-list 20.1.1.1 [SwitchA-dhcp-pool-0] option 121 hex 18 14 01 01 0A 01 01 02 [SwitchA-dhcp-pool-0] quit
# Enable DHCP.
[SwitchA] dhcp enable
Configure Switch B:
# Configure VLAN-interface 2 to use DHCP for IP address acquisition.
<SwitchB> system-view [SwitchB] interface vlan-interface 2 [SwitchB-Vlan-interface2] ip address dhcp-alloc [SwitchB-Vlan-interface2] quit
Verifying the configuration
# Display the IP address and other network parameters assigned to Switch B.
[SwitchB-Vlan-interface2] display dhcp client verbose Vlan-interface2 DHCP client information: Current state: BOUND Allocated IP: 10.1.1.3 255.255.255.0 Allocated lease: 864000 seconds, T1: 331858 seconds, T2: 756000 seconds Lease from May 21 19:00:29 2012 to May 31 19:00:29 2012 DHCP server: 10.1.1.1 Transaction ID: 0xcde72232 Classless static routes: Destination: 20.1.1.0, Mask: 255.255.255.0, NextHop: 10.1.1.2 DNS servers: 20.1.1.1 Client ID type: acsii(type value=00) Client ID value: 000c.29d3.8659-Vlan2 Client ID (with type) hex: 0030-3030-632e-3239- 6433-2e38-3635-392d- 4574-6830-2f30-2f32 T1 will timeout in 3 days 19 hours 48 minutes 43 seconds
# Display the route information on Switch B. The output shows that a static route to subnet 20.1.1.0/24 is added to the routing table.
[SwitchB] display ip routing-table Destinations : 11 Routes : 11 Destination/Mask Proto Pre Cost NextHop Interface 10.1.1.0/24 Direct 0 0 10.1.1.3 Vlan2 10.1.1.3/32 Direct 0 0 127.0.0.1 InLoop0 20.1.1.0/24 Static 70 0 10.1.1.2 Vlan2 10.1.1.255/32 Direct 0 0 10.1.1.3 Vlan2 127.0.0.0/8 Direct 0 0 127.0.0.1 InLoop0 127.0.0.0/32 Direct 0 0 127.0.0.1 InLoop0 127.0.0.1/32 Direct 0 0 127.0.0.1 InLoop0 127.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0 224.0.0.0/4 Direct 0 0 0.0.0.0 NULL0 224.0.0.0/24 Direct 0 0 0.0.0.0 NULL0 255.255.255.255/32 Direct 0 0 127.0.0.1 InLoop0