Contents
Lease Time Guidelines
The default DHCP lease time is 1 day, which is well suited for nets with low turnover (i.e. the population of client machines is fairly stable and doesn’t change much).
Network administrators may choose to configure a different lease time on individual IPv4 DHCP Ranges (Dynamic Pools), subject to the following guidelines which are designed to keep overall load on the DHCP servers from growing unsustainably:
| Lease time | Guideline |
|---|---|
| 1 day or longer | Recommended for most networks |
| between 4 hours and 1 day | No problem, use freely where desired for IPv4 nets with higher host turnover |
| between 1 hour and 4 hours | Acceptable, but please exercise good judgment and use only where necessary |
| less than 1 hour | Requires approval from service manager |
Because IPv6 subnets are so spacious, there is generally no reason to reduce the DHCPv6 lease time parameters; IPv6 nets with higher host turnover which require Stateful autoconfiguration can simply be configured with larger DHCP Ranges in order to avoid running out of leases.
Range Size Guidelines
IPv4 DHCP Ranges (Dynamic Pools) should be sized so that the number of unassigned IP addresses in the Range (after all desired clients have obtained their leases, and not counting any addresses within Exclusion Ranges) will be at least 1-5% of the total, with a minimum of at least 2 unassigned IP addresses (even for very small Ranges) in order to properly utilize the redundancy provided by DHCP Failover.
| Total Addresses in Range | Minimum Unassigned Addresses |
|---|---|
| 3-40 | at least 2 addresses |
| 41-200 | at least 2-10 addresses (1-5% of total) |
| 201+ | at least 1-5% of total |
Note: Email Alert thresholds should also be adjusted accordingly (to higher than 95%) if the expected number of unassigned IP addresses is less than 5% of the total.
Service Defaults
The following DHCP settings serve as defaults; they are configured at the top level of the Grid hierarchy and automatically inherited by all Networks. An individual Network, DHCP Range, DHCP Fixed Address, or DHCP-enabled Host can override one of these defaults by specifying its own value for the setting.
Client options
For DHCPv4:
| code | name | value |
|---|---|---|
| 6 | domain-name-servers |
130.126.2.131 |
| 42 | ntp-servers |
130.126.24.24, 130.126.24.44, 130.126.24.53 |
| 252 | wpad-url |
” ” (a blank space) |
For DHCPv6:
| code | name | value |
|---|---|---|
| 23 |
|
2620:0:e00:a::1 |
Service settings
For DHCPv4:
- Lease Time: 1 day (see Lease Time Guidelines above)
- Authoritative: true
-
Ping Check: 1 request, with 1 second timeout
This setting cannot be overridden for individual Networks or Ranges.
-
Enable DDNS Updates: false
ddns-updates false prevents the DHCP server from attempting to do dynamic DNS updates on behalf of clients that choose to send a Client FQDN value in their DHCPREQUEST. This setting is not one of the options transmitted to clients, and will not affect their ability to perform their own dynamic DNS updates in Active Directory (or any other DDNS server).
For DHCPv6:
- Valid Lifetime: 2 days
-
Preferred Lifetime: 1 day
- Enable DDNS Updates: false