Users Guide

Table Of Contents
In this scenario the DHCP clients (Host 1, 2, 3) are part of the VRF Blue. The DHCP packet sent by these DHCP clients reach
the DHCP relay in VLAN 10 in the VRF Blue. In the VLAN 10, you must configure the helper-address with the DHCP server
reachable VRF services. DHCP relay forwards the DHCP client packets to the DHCP server without route leaking by forwarding
it in the services VRF. The DHCP relay appends the option 82 and its following sub options:
Link selection option (sub option 5) set to the IP address of the VLAN 10.
Server-override option (sub option 11) set to the IP address of the VRRP virtual IP or anycast gateway IP.
VSS option (sub option 151 and sub option 152) set to the VRF Blue.
You must configure VLAN 20 on interface Ethernet 1/1/4 as source interface, which sets the giaddr field in the BOOTP
relay request packet towards the DHCP server.
The BOOTP relay reply packet from the DHCP server contains the destination IP address set to the IP address of the source
interface (VLAN 20). This interface is forwarded to the DHCP client by the DHCP relay in VRF Blue after removing the DHCP
option 82 and its relay sub options.
The DHCP server allocates the IP address to the DHCP client based on the link selection and VSS options. The DHCP unicast
packet from the DHCP client is sent to the server-override IP. After appending the option 82 and its sub options, DHCP relay
forwards this packet to the DHCP server.
VRRP Virtual IP as Server Override (sub option 11)
The server identifier (server ID) override sub-option allows the DHCP relay agent to specify a new value for the server ID
option. This option inserted by the DHCP server in the BOOTPReply packet.
This sub-option allows the DHCP relay agent to act as a proxy to the actual DHCP server, such that the renew requests come
to the relay agent rather than to the DHCP server directly.
The server ID override sub-option contains the IP address on the relay agent that is accessible from the client. Using this
information, the DHCP client sends all the DHCP unicast packet (RENEW, RELEASE, DECLINE) to the relay agent. The
relay agent adds all the appropriate option 82 sub-options and then forwards it to the configured helper-address for further
processing.
System management
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