Administrator Guide

Dell(conf-if-vl-4)# tagged TenGigE 1/4
Dell(conf-if-vl-4)# ip helper-address vrf vrf1 100.0.0.1
Dell(conf-if-vl-4)# ipv6 helper-address vrf vrf1 100::1
Configure the System for User Port Stacking
(Option 230)
Set the stacking-option variable to provide stack-port detail on the DHCP server when you set the DHCP offer. A stack can be formed
when the units are connected.
Option 230 is the option for user port stacking. Use it to create up to eight stack groups. Define the configuration parameters on the
DHCP server for each chassis based on the chassis MAC address. Configure the following parameters:
• unit number
• priority
• stack group ID
The received stacking configuration is always applied on the master stack unit.
option #230 "unit-number:3#priority:2#stack-group:14"
Configure Secure DHCP
DHCP as defined by RFC 2131 provides no authentication or security mechanisms. Secure DHCP is a suite of features that protects
networks that use dynamic address allocation from spoofing and attacks.
• Option 82
• DHCP Snooping
• Dynamic ARP Inspection
• Source Address Validation
Option 82 (DHCPv4 relay options)
RFC 3046 (the relay agent information option, or Option 82) is used for class-based IP address assignment.
The code for the relay agent information option is 82, and includes two suboptions, circuit ID and remote ID.
Circuit ID
This is the interface on which the client-originated message is received.
Remote ID This identifies the host from which the message is received. The value of this suboption is the MAC address of
the relay agent that adds Option 82.
In DHCPv4 relay , the Option 82 is not added by default. When the ip dhcp relay information-option is configured, the Option
82 with suboptions 1 (Agent Circuit ID) and 2 ( Agent Remote ID) are added to the relayed DHCP packet. The default values of the
suboptions are as follows:
• Default Agent Circuit ID is constructed in the format VLANID:LagID:SlotID:PortStr. When the port is fanned-out, the
PortStr is represented as mainPort:subPort (all in ASCII format).
• Default Agent Remote ID is the system MAC address (in binary format).
The following example shows the format of the Circuit ID - 723:0:1:1.
Table 28. Circuit ID Format
VLAN ID LAG ID Slot ID Port Str
723 0 1 1
The DHCP relay agent inserts Option 82 before forwarding DHCP packets to the server. The server can use this information to:
• Track the number of address requests per relay agent. Restricting the number of addresses available per relay agent can harden a
server against address exhaustion attacks.
• Associate client MAC addresses with a relay agent to prevent offering an IP address to a client spoofing the same MAC address on a
different relay agent.
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Dynamic Host Configuration Protocol (DHCP)