Deployment Guide

Table Of Contents
Debugging the IPv6 DHCP
To debug the IPv6 DHCP, use the following command.
Display debug information for IPV6 DHCP.
EXEC Privilege mode
debug ipv6 dhcp
IPv6 DHCP Snooping MAC-Address Verification
Configure to enable verify source mac-address in the DHCP packet against the mac address stored in the snooping binding
table.
Enable IPV6 DHCP snooping .
CONFIGURATION mode
ipv6 dhcp snooping verify mac-address
Configuring the DHCP secondary-subnet
DHCP Secondary subnet feature is an extended feature of DHCP relay agent. After enabling DHCP Relay Secondary Subnet,
relay agent tries to get IP Address from secondary IP Address subnet pool, only when relay agent fails to get IP Address through
primary IP Address.
1. To enable all the DHCP relay secondary subnet interfaces.
CONFIGURATION mode
ip dhcp relay secondary-subnet
2. Sample Configuration:
Dell(conf)#ip dhcp relay secondary-subnet
Dell(conf)#interface TenGigabitEthernet 0/0
Dell(conf-if-te-0/0)#ip address 10.1.1.1/24
Dell(conf-if-te-0/0)#ip address 11.1.1.1/24 secondary
Dell(conf-if-te-0/0)#ip helper-address 2.1.1.1
Dell(conf-if-te-0/0)#no shutdown
Dell(conf-if-te-0/0)#
DHCP relay tries to get ip address for the client, through configured primary address filling giaddr (relay address) 10.1.1.1.
If there is no OFFER from DHCP Server, for three DISCOVER retries. Since secondary-subnet enabled, DHCP Relay Agent
tries to get ip address through secondary ip address filling giaddr (relay address) 11.1.1.1.
3. To disable the DHCP relay secondary-subnet:
Dell(conf)# no ip dhcp relay secondary-subnet
Drop DHCP Packets on Snooped VLANs Only
Binding table entries are deleted when a lease expires or the relay agent encounters a DHCPRELEASE.
Line cards maintain a list of snooped VLANs. When the binding table fills, DHCP packets are dropped only on snooped
VLANs, while such packets are forwarded across non-snooped VLANs. Because DHCP packets are dropped, no new IP address
assignments are made. However, DHCP release and decline packets are allowed so that the DHCP snooping table can decrease
in size. After the table usage falls below the maximum limit of 4000 entries, new IP address assignments are allowed.
To view the number of entries in the table, use the show ip dhcp snooping binding command. This output displays the
snooping binding table created using the ACK packets from the trusted port.
DellEMC#show ip dhcp snooping binding
Codes : S - Static D - Dynamic
302
Dynamic Host Configuration Protocol (DHCP)