Concept Guide

IPv6 conguration, and two dierent loopback interfaces (loopback 2 and 3). DHCP relay forwards packets using the loopback 2
interface with IPv4 and IPv6 addresses ((2.2.2.2/32 and 2::2/128) from Vlan 2. The same way, the relay uses IPv4 and IPv6 addresses
(3.3.3.3/32 and 3::3/128) of loopback 3 interface from Vlan 3.
Dell(conf)# interface Vlan 2
Dell(conf-if-vl-2)# ip vrf forwarding vrf1
Dell(conf-if-vl-2)# ip address 2.0.0.1/24
Dell(conf-if-vl-2)# ipv6 address 2::1/64
Dell(conf-if-vl-2)# tagged fortyGigE 0/0
Dell(conf-if-vl-2)# ip helper-address vrf vrf1 100.0.0.1
Dell(conf-if-vl-2)# ipv6 helper-address vrf vrf1 100::1
Dell(conf-if-vl-2)# ip dhcp relay source-interface loopback 2
Dell(conf-if-vl-2)# ipv6 dhcp relay source-interface loopback 2
Dell(conf)# interface Vlan 4
Dell(conf-if-vl-4)# ip vrf forwarding vrf1
Dell(conf-if-vl-4)# ip address 4.0.0.1/24
Dell(conf-if-vl-4)# ipv6 address 4::1/64
Dell(conf-if-vl-4)# tagged fortyGigE 0/4
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
Dell(conf-if-vl-4)# ip dhcp relay source-interface loopback 3
Dell(conf-if-vl-4)# ipv6 dhcp relay source-interface loopback 3
3 In the below conguration, the DHCP relay source interface is not congured in the VLAN interface. So, the DHCP relay uses the
congured global DHCP relay source interface to forward the packets from the DHCP client to server.
Dell(conf)# interface Vlan 5
Dell(conf-if-vl-4)# ip vrf forwarding vrf1
Dell(conf-if-vl-4)# ip address 4.0.0.1/24
Dell(conf-if-vl-4)# ipv6 address 4::1/64
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
Congure Secure DHCP
DHCP as dened 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 spoong and attacks.
• Option 82
• DHCP Snooping
• Dynamic ARP Inspection
• Source Address Validation
Option 82
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 is comprised of two sub-options, circuit ID and remote ID.
Circuit ID
This is the interface on which the client-originated message is received.
Remote ID This identies the host from which the message is received. The value of this sub-option 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 congured, the Option
82 with sub-options 1 (Agent Circuit ID) and 2 ( Agent Remote ID) are added to the relayed DHCP packet. The default values of the sub-
options are as follows:
• Default Agent Circuit ID is constructed in the format “VlanID:LagID:SlotId:PortId”
• Default Agent Remote ID is the system MAC address (in binary format)
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Dynamic Host Conguration Protocol (DHCP)