Dell S4820T, Configuration Manual

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DHCPNAK A server sends this message to the client if it is not able to fulfill a DHCPREQUEST;
for example, if the requested address is already in use. In this case, the client starts
the configuration process over by sending a DHCPDISCOVER.
Figure 36. Client and Server Messaging
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 attempt 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 attempt 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 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. 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.
Dynamic Host Configuration Protocol (DHCP)
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