Configure Segment DHCP Properties

DHCP configuration is a per-segment property. In the default configuration the Compute Gateway DHCP server handles DHCP requests from VMs on all routed segments. If you have an external DHCP server that manages IP addresses on your workload networks, you can configure the segment to use DHCP relay. You can also configure the segment to use its own local DHCP Server.

Per-segment DHCP configuration is part of the segment create/update workflow document in Create or Modify a Network Segment.

Procedure

Log in to the VMware Cloud on AWS GovCloud at https://www.vmc-us-gov.vmware.com/.
Click Networking & Security > Segments.
To modify the DHCP configuration of an existing segment, click its ellipsis button an select Edit, then EDIT DHCP CONFIG.

Choose a DHCP Type and specify configuration details.

Configuration details depend on the DHCP type. To specify Settings, toggle DHCP Config to Enabled.

DHCP Type	Description
Local DHCP Server	Select this option to create a local DHCP server that has an IP address on the segment. As the name suggests, it is a DHCP server that is local to the segment and not available to the other segments in the network. A local DHCP server provides a dynamic IP assignment service only to the VMs that are attached to the segment. You can configure all DHCP settings, including DHCP ranges, DHCP Options, and static bindings on the segment. For disconnected segments, this type is selected by default.
DHCP Relay	Select this option to relay the DHCP client requests to the external DHCP servers. The external DHCP servers can be in any subnet, outside the SDDC, or in the physical network. The DHCP relay service is local to the segment and not available to the other segments in the network.
Gateway DHCP Server	This DHCP type is analogous to a central DHCP service that dynamically assigns IP and other network configuration to the VMs on all the segments that are connected to the gateway and using Gateway DHCP. Depending on the type of DHCP profile you attach to the gateway, you can configure a Gateway DHCP server or a Gateway DHCP relay on the segment. By default, segments that are connected to a tier-1 or tier-0 gateway use Gateway DHCP. If needed, you can choose to configure a DHCP local server or a DHCP relay on the segment. To configure Gateway DHCP on a segment, a DHCP profile must be attached to the gateway. See Create or Modify a DHCP Profile.

DHCP Type

Description

Local DHCP Server

Select this option to create a local DHCP server that has an IP address on the segment.

As the name suggests, it is a DHCP server that is local to the segment and not available to the other segments in the network. A local DHCP server provides a dynamic IP assignment service only to the VMs that are attached to the segment.

You can configure all DHCP settings, including DHCP ranges, DHCP Options, and static bindings on the segment.

For disconnected segments, this type is selected by default.

DHCP Relay

Select this option to relay the DHCP client requests to the external DHCP servers. The external DHCP servers can be in any subnet, outside the SDDC, or in the physical network.

The DHCP relay service is local to the segment and not available to the other segments in the network.

Gateway DHCP Server

This DHCP type is analogous to a central DHCP service that dynamically assigns IP and other network configuration to the VMs on all the segments that are connected to the gateway and using Gateway DHCP. Depending on the type of DHCP profile you attach to the gateway, you can configure a Gateway DHCP server or a Gateway DHCP relay on the segment.

By default, segments that are connected to a tier-1 or tier-0 gateway use Gateway DHCP. If needed, you can choose to configure a DHCP local server or a DHCP relay on the segment.

To configure Gateway DHCP on a segment, a DHCP profile must be attached to the gateway. See Create or Modify a DHCP Profile.

Enable the DHCP configuration settings on the subnet by clicking the DHCP Config toggle button.
In the DHCP Server Address text box, enter the IP addresses.
- If you are configuring a DHCP local server, server IP address is required. A maximum of two server IP addresses are supported. One IPv4 address and one IPv6 address. For an IPv4 address, the prefix length must be <= 30, and for an IPv6 address, the prefix length must be <= 126. The server IP addresses must belong to the subnets that you have specified in this segment. The DHCP server IP address must not overlap with the IP addresses in the DHCP ranges and DHCP static binding. The DHCP server profile might contain server IP addresses, but these IP addresses are ignored when you configure a local DHCP server on the segment.
  After a local DHCP server is created, you can edit the server IP addresses on the Set DHCP Config page. However, the new IP addresses must belong to the same subnet that is configured in the segment.
- If you are configuring a DHCP relay, this step is not applicable. The server IP addresses are fetched automatically from the DHCP relay profile and displayed below the profile name.
- If you are configuring a Gateway DHCP server, this text box is not editable. The server IP addresses are fetched automatically from the DHCP profile that is attached to the connected gateway.
  Remember, the Gateway DHCP server IP addresses in the DHCP server profile can be different from the subnet that is configured in the segment. In this case, the Gateway DHCP server connects with the IPv4 subnet of the segment through an internal relay service, which is autocreated when the Gateway DHCP server is created. The internal relay service uses any one IP address from the subnet of the Gateway DHCP server IP address. The IP address used by the internal relay service acts as the default gateway on the Gateway DHCP server to communicate with the IPv4 subnet of the segment.
  After a Gateway DHCP server is created, you can edit the server IP addresses in the DHCP profile of the gateway. However, you cannot change the DHCP profile that is attached to the gateway.
DHCP Ranges, if specified, must meet the following requirements:
- IP addresses in the DHCP ranges must belong to the subnet that is configured on the segment. DHCP ranges cannot contain IP addresses from multiple subnets.
- IP ranges must not overlap with the DHCP Server IP address and the DHCP static binding IP addresses.
- IP ranges in the DHCP IP pool must not overlap each other.
- Number of IP addresses in any DHCP range must not exceed 65536.
(Optional) Edit the lease time in seconds.
Default value is 86400. Valid range of values is 60–4294967295. The lease time configured in the DHCP server configuration takes precedence over the lease time that you specified in the DHCP profile.
(Optional) Enter the IP address of the domain name server (DNS) to use for name resolution. A maximum of two DNS servers are permitted.
When not specified, no DNS is assigned to the DHCP client. DNS server IP addresses must belong to the same subnet as the subnet's gateway IP address.
(Optional) Click Options to configure DHCP options.
For information about CLASSLESS STATIC ROUTES and other DHCP Options, see RFC3442 and Create a DHCP Server in the NSX-T Data Center Administration Guide.

(Optional) Specify a DHCP Profile. If your SDDC includes more than one DHC Profile, you can use the DHCP Profile drop-down menu to select the name of DHCP server profile you want this segment to use.
See Create or Modify a DHCP Profile.
Click APPLY to apply the DHCP configuration to the segment.