Reference Guide

Implementation Information
The following describes DHCP implementation.
• Dell Networking implements DHCP based on RFC 2131 and RFC 3046.
• IP source address validation is a sub-feature of DHCP Snooping; the Dell Networking operating system (FTOS)
uses access control lists (ACLs) internally to implement this feature and as such, you cannot apply ACLs to an
interface which has IP source address validation. If you configure IP source address validation on a member
port of a virtual local area network (VLAN) and then attempt to apply an access list to the VLAN, FTOS displays
the first line in the following message. If you first apply an ACL to a VLAN and then attempt enable IP source
address validation on one of its member ports, FTOS displays the second line in the following message.
% Error: Vlan member has access-list configured.
% Error: Vlan has an access-list configured.
NOTE: If you enable DHCP Snooping globally and you have any configured L2 ports, any IP ACL, MAC ACL,
or DHCP source address validation ACL does not block DHCP packets.
• FTOS provides 40K entries that can be divided between leased addresses and excluded addresses. By
extension, the maximum number of pools you can configure depends on the subnet mask that you give to each
pool. For example, if all pools were configured for a /24 mask, the total would be 40000/253 (approximately 158). If
the subnet is increased, more pools can be configured. The maximum subnet that can be configured for a single
pool is /17. FTOS displays an error message for configurations that exceed the allocated memory.
• The S4820T supports 4K DHCP Snooping entries.
• All platforms support Dynamic ARP Inspection on 16 VLANs per system. For more information, refer to Dynamic
ARP Inspection.
NOTE: If the DHCP server is on the top of rack (ToR) and the VLTi (ICL) is down due to a failed link, when a
VLT node is rebooted in JumpStart mode, it is not able to reach the DHCP server, resulting in bare metal
provisioning (BMP) failure.
Configure the System to be a DHCP Server
Configuring the system to be a DHCP server is supported only on the S4810 S4820T platform.
A DHCP server is a network device that has been programmed to provide network configuration parameters to clients
upon request. Servers typically serve many clients, making host management much more organized and efficient.
The following table lists the key responsibilities of DHCP servers.
Table 18. DHCP Server Responsibilities
DHCP Server Responsibility Description
Address Storage and Management DHCP servers are the owners of the addresses used by
DHCP clients.The server stores the addresses and
manages their use, keeping track of which addresses
have been allocated and which are still available.
Configuration Parameter Storage and Management DHCP servers also store and maintain other parameters
that are sent to clients when requested. These parameters
specify in detail how a client is to operate.
Lease Management DHCP servers use leases to allocate addresses to clients
for a limited time. The DHCP server maintains information
about each of the leases, including lease length.
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