Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.100.0 - Page 272

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 OS 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 to apply an access list to the VLAN, Dell Networking OS displays the first line in the following message. If you first apply an ACL to a VLAN and then enable IP source address validation on one of its member ports, Dell Networking OS 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. • Dell Networking OS provides 40000 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. Dell Networking OS displays an error message for configurations that exceed the allocated memory. • This platform supports 4000 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 BMP (Bare Metal Provisioning) mode, it is not able to reach the DHCP server, resulting in BMP failure. Configure the System to be a DHCP Server 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 22. DHCP Server Responsibilities DHCP Server Responsibilities Address Storage and Management Configuration Parameter Storage and Management Lease Management Responding To Client Requests Providing Administration Services Description 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. 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. 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. DHCP servers respond to different types of requests from clients, primarily, granting, renewing, and terminating leases. DHCP servers include functionality that allows an administrator to implement policies that govern how DHCP performs its other tasks. 272 Dynamic Host Configuration Protocol (DHCP)