391
Configuring DHCP
Information About Configuring DHCP
Figure 60
DHCP Relay Agent in a Metropolitan Ethernet Network
When you enable the DHCP snooping information option-82 on the switch, this sequence of events occurs:
The host (DHCP client) generates a DHCP request and broadcasts it on the network.
When the switch receives the DHCP request, it adds the option-82 information in the packet. By default, the
remote-ID suboption is the switch MAC address, and the circuit-ID suboption is the port identifier,
vlan-mod-port
,
from which the packet is received.
If the IP address of the relay agent is configured, the switch adds this IP address in the DHCP packet.
The switch forwards the DHCP request that includes the option-82 field to the DHCP server.
The DHCP server receives the packet. If the server is option-82-capable, it can use the remote ID, the circuit ID, or
both to assign IP addresses and implement policies, such as restricting the number of IP addresses that can be
assigned to a single remote ID or circuit ID. The DHCP server then repeats the option-82 field in the DHCP reply.
The DHCP server unicasts the reply to the switch if the request was relayed to the server by the switch. The switch
verifies that it originally inserted the option-82 data by inspecting the remote ID and possibly the circuit ID fields. The
switch removes the option-82 field and forwards the packet to the switch port that connects to the DHCP client that
sent the DHCP request.
In the default suboption configuration, when the described sequence of events occurs, the values in these fields in
Circuit-ID suboption fields
—
Suboption type
—
Length of the suboption type
—
Circuit-ID type
—
Length of the circuit-ID type
Remote-ID suboption fields
—
Suboption type
—
Length of the suboption type
—
Remote-ID type
Subscribers
Catalyst switch
(DHCP relay agent)
Host A
(DHCP client)
Access layer
DHCP
server
Host B
(DHCP client)
98813
VLAN 10
Содержание IE 4000
Страница 12: ...8 Configuration Overview Default Settings After Initial Switch Configuration ...
Страница 52: ...48 Configuring Interfaces Monitoring and Maintaining the Interfaces ...
Страница 108: ...104 Configuring Switch Clusters Additional References ...
Страница 128: ...124 Performing Switch Administration Additional References ...
Страница 130: ...126 Configuring PTP ...
Страница 140: ...136 Configuring CIP Additional References ...
Страница 146: ...142 Configuring SDM Templates Configuration Examples for Configuring SDM Templates ...
Страница 192: ...188 Configuring Switch Based Authentication Additional References ...
Страница 244: ...240 Configuring IEEE 802 1x Port Based Authentication Additional References ...
Страница 274: ...270 Configuring SGT Exchange Protocol over TCP SXP and Layer 3 Transport Configuring Cisco TrustSec Caching ...
Страница 298: ...294 Configuring VLANs Additional References ...
Страница 336: ...332 Configuring STP Additional References ...
Страница 408: ...404 Configuring DHCP Additional References ...
Страница 450: ...446 Configuring IGMP Snooping and MVR Additional References ...
Страница 490: ...486 Configuring SPAN and RSPAN Additional References ...
Страница 502: ...498 Configuring Layer 2 NAT ...
Страница 559: ...555 Configuring Network Security with ACLs How to Configure Network Security with ACLs Creating a Numbered Extended ACL ...
Страница 770: ...766 Configuring IPv6 MLD Snooping Related Documents ...
Страница 930: ...926 Configuring IP Unicast Routing Related Documents ...
Страница 956: ...952 Configuring IPv6 Unicast Routing Configuring IPv6 network 2010 AB8 2 48 network 2010 AB8 3 48 exit address family ...
Страница 976: ...972 Configuring Cisco IOS IP SLAs Operations Additional References ...
Страница 978: ...974 Dying Gasp ...
Страница 990: ...986 Configuring Enhanced Object Tracking Monitoring Enhanced Object Tracking ...
Страница 994: ...990 Configuring MODBUS TCP Displaying MODBUS TCP Information ...
Страница 996: ...992 Ethernet CFM ...
Страница 1030: ...1026 Working with the Cisco IOS File System Configuration Files and Software Images Working with Software Images ...
Страница 1066: ...1062 Using an SD Card SD Card Alarms ...