DHCP Server Defaults

Configuration > Networking > DHCP Server Defaults

You can reduce your workload by using this tab to configure global defaults for Dynamic Host Configuration Protocol (DHCP).

These defaults apply to the LAN interfaces in Deployment Profiles that specify Router mode.
There are three choices:
- No DHCP/No RA.
- Each LAN interface acts as a DHCP Server.
  
  NOTE: If you enable DHCP Failover, you must use the same interface label for each physical interface.
- The EdgeConnect appliance acts as a DHCP/BOOTP Relay between a DHCP server at a data center and clients needing an IP address.
On the Configuration > Overlays & Security > Deployment Profiles tab, the selected default displays consistently under each LAN–side IP/Mask field.

For any LAN–side interface, you can override the global default by clicking the DHCP-related link under the IP/Mask field and changing the values or selection.
Changes you save to the global default only apply to new configurations.
To view or revise the list of reserved subnets, select Monitoring.
Before you can configure DHCP, you must navigate to Management Services and select an interface for DHCP Relay. See Management Services for more information.

If the LAN interface has an IPv4 IP address, click V4 to display the DHCP configuration settings. See V4.

If the LAN interface has an IPv6 IP address, click V6 to display the Router Advertisement settings. See V6.

DHCP Settings / Router Advertisements

V4

The following tables describe the various DHCP settings you can configure for LAN interfaces that have IPv4 IP addresses.

DHCP Server

Field	Description
DHCP Pool Subnet/Mask	Enter the DHCP pool subnet and mask IP addresses.
Subnet Mask	Mask that specifies the default number of IP addresses reserved for any subnet. For example, entering 24 reserves 256 IP addresses.
Exclude first N addresses	Specifies how many IP addresses are not available at the beginning of the subnet’s range.
Exclude last N addresses	Specifies how many IP addresses are not available at the end of the subnet’s range.
Default lease, Maximum lease	Specify, in hours, how long an interface can keep a DHCP–assigned IP address.
Default gateway	Indicates whether the default gateway is being used.
DNS server(s)	Specifies the associated Domain Name System servers.
NTP server(s)	Specifies the associated Network Time Protocol servers.
NetBIOS name server(s)	Used for Windows (SMB) type sharing and messaging. It resolves the names when you are mapping a drive or connecting to a printer.
NetBIOS node type	NetBIOS node type of a networked computer relates to how it resolves NetBIOS names to IP addresses. There are four node types: B-node – 0x01 Broadcast P-node – 0x02 Peer (WINS only) M-node – 0x04 Mixed (broadcast, then WINS) H-node – 0x08 Hybrid (WINS, then broadcast)
DHCP failover	Enables DHCP failover. To set it up, click the Failover Settings link.

DHCP/BOOTP Relay

Field	Description
Destination DHCP/BOOTP Server	IP address of the DHCP server assigning the IP addresses.
Common DHCP server for all segments	Select this check box to set the default values for all segments. HINT: You can reset the defaults in Management Services by setting the DHCP Relay interface to “any” and then selecting an interface label again. However, this might impact service. Or, you can manually reset the defaults by selecting the following values: Option 82 = enabled, Option 82 Policy = append, and select the following sub options: 1, 5, 10, 11, 151, and 152.
Distinct DHCP server per segment	Select this option to override the DHCP relay configuration set in the Manages Services tab with the settings you select in this dialog box.
Enable Option 82	When selected, inserts additional information into the packet header to identify the client’s point of attachment. This setting applies to all LAN-side interfaces on this appliance. IMPORTANT: Changing this setting will modify Option 82 settings on all LAN-side interfaces that are enabled as DHCP Relay.
Option 82 Policy	Tells the relay what to do with the hex string it receives. The choices are append, replace, forward, and discard. This setting applies to all LAN-sideinterfaces on this appliance. IMPORTANT: Changing this setting will modify Option 82 settings on all LAN-side interfaces that are enabled as DHCP Relay.
Sub Options	Select one or more of the following: 1 - Agent Circuit ID: Provides information about the interface or circuit through which the DHCP request was received. 5 - Link selection: Specifies the IP address used by the DHCP server to determine the appropriate subnet for addressing the DHCP client. 10 - Client Unicast/Broadcast Indication flag: Indicates whether the DHCP relay received the client packet as a unicast or broadcast packet. 11 - Server ID Override: Allows the DHCP relay agent to act as a proxy for the DHCP server to process unicast lease renewals. 150 - Link selection (Cisco proprietary): Provides information about a segment or VPN that is necessary to allocate an address to a DHCP client on that segment. 151 - VRF name/VPN ID 152 - VRF name/VPN ID Control Sub-Option OR Server ID Override (Cisco proprietary): Indicates whether the DHCP server supports sub option 151 (VRF Name/VPN ID). If this option is present in the reply from the server, the server does not support option 151.

V6

The following table describe the various router advertisement settings you can configure for LAN interfaces that have IPv6 IP addresses. The LAN interface will use these options to autoconfigure IPv6 addresses and to learn default gateway addresses.

NOTE: DHCP for IPv6 is not supported.

Setting	Description
Enable Router Advertisements	Specifies whether the router should send RA messages.
Managed Flag	Select this option to instruct IPv6 hosts to use DHCPv6 to obtain their IPv6 addresses in addition to any other configuration information.
Other Flag	Select this option to instruct IPv6 hosts to use DHCPv6 to obtain additional configuration information, such as DNS server addresses and other network parameters.
Link MTU	Set the maximum transmission unit (MTU) size that can be transmitted without fragmentation. This helps ensure that all hosts on the network use the same MTU, avoiding issues related to packet fragmentation and reassembly.
Max Interval	Specify the maximum interval in seconds between unsolicited RA messages. This helps to control the frequency of RA messages.
Min Interval	Specify the minimum interval in seconds between unsolicited RA messages. This helps to control the frequency of RA messages.
Current Hop Limit	Set the default hop limit for IPv6 packets sent by hosts on the network. Hosts use this value to configure their own hop limit for outgoing packets.
Default Router Preference	Select High, Medium, or Low to set the preference level of the router for use as a default router. Hosts use this value to prioritize multiple routers on the same link.
Default Router Lifetime	Specify the lifetime in seconds of the default route that is advertised by the router. The hosts use this value to determine how long the router should be used as the default gateway.
Reachable Time	Specify the time in milliseconds that an IPv6 host considers a neighbor reachable after receiving a confirmation. This value maintains accurate and timely reachability information in the neighbor cache.
Retrans Timer	Specify the time in milliseconds between retransmissions of neighbor solicitation messages. This value reduces the frequency of retries when attempting to discover or confirm the reachability of neighbors on the network.

Add a Router Advertisement Prefix

Click Add and complete the following fields. You can create up to 10 prefixes.

Setting	Description
Prefix-id	The ID assigned to the prefix.
Prefix	Select whether the prefix can be used by hosts for SLAAC. When set to true, hosts can use the prefix to generate their own IPv6 addresses.
Autonomous flag	Select whether the prefix can be used by hosts for SLAAC. When set to true, hosts can use the prefix to generate their own IPv6 addresses.
Onlink flag	Specifies whether the prefix is on-link, which affects how hosts handle routing for addresses within the prefix. If set to true, hosts assume that addresses within the prefix can be reached directly on the local network segment.
Valid Lifetime	Specify the duration in seconds for which the advertised prefix is valid.
Preferred Lifetime	Specify the duration in seconds (relative to the time the packet is sent) that addresses generated from the prefix via stateless address auto-configuration remain preferred.