DHCP
The Fabric includes an integrated DHCP server that dinamically assigns IP addresses to hosts connected to VPC subnets. The DHCP server supports dynamic IP allocation, static leases, and various configuration options.
Overview
The DHCP server is configured per VPC subnet and provides:
- Dynamic IP allocation from a configurable range
- Static leases for specific MAC addresses
- DHCP options including DNS servers, NTP servers, PXE boot, MTU, and custom routes
- DHCP relay support for third-party DHCP servers
Basic Configuration
Enabling DHCP
To enable DHCP for a VPC subnet, set dhcp.enable: true in the subnet configuration:
apiVersion: vpc.githedgehog.com/v1beta1
kind: VPC
metadata:
name: vpc-1
namespace: default
spec:
subnets:
default: # Subnet name (can be any name you choose)
subnet: 10.10.1.0/24
gateway: 10.10.1.1
vlan: 1001
dhcp:
enable: true
With this minimal configuration, the DHCP server will:
- Use all available IPs in the subnet (excluding the gateway)
- Provide a default lease time of 3600 seconds (1 hour)
- Configure the VPC gateway as the default route
Specifying an IP Range
You can limit the DHCP pool to a specific range of IP addresses:
This reserves IPs outside the range (e.g., 10.10.1.2-10.10.1.9 and 10.10.1.100-10.10.1.254) for static assignments or other purposes.
CLI Usage
Use the kubectl fabric vpc create command with DHCP options:
kubectl fabric vpc create \
--name vpc-1 \
--subnet 10.10.1.0/24 \
--vlan 1001 \
--dhcp \
--dhcp-start 10.10.1.10
After creating the VPC, attach it to servers using their connection names:
kubectl fabric vpc attach \
--vpc vpc-1 \
--subnet default \
--connection server-01--mclag--leaf-01--leaf-02
CLI Limitations
The CLI does not currently support configuring static leases or advanced DHCP options. Use YAML configuration with kubectl apply -f for these features.
DHCP Options
The DHCP server supports various options to customize network configuration for clients:
apiVersion: vpc.githedgehog.com/v1beta1
kind: VPC
metadata:
name: vpc-1
namespace: default
spec:
subnets:
default:
subnet: 10.10.1.0/24
gateway: 10.10.1.1
vlan: 1001
dhcp:
enable: true
range:
start: 10.10.1.10
end: 10.10.1.99
options:
leaseTimeSeconds: 7200 # 2 hours
dnsServers:
- 1.1.1.1
- 8.8.8.8
timeServers: # NTP servers
- 132.163.96.1
- 132.163.96.2
interfaceMTU: 9000 # Jumbo frames
pxeURL: tftp://10.10.10.99/bootfile # PXE boot server
disableDefaultRoute: false # Manage default route
advertisedRoutes: # Custom static routes
- destination: 10.20.0.0/16
gateway: 10.10.1.2
- destination: 10.30.0.0/16
gateway: 10.10.1.3
Option Details
| Option | Description | DHCP Option | Default |
|---|---|---|---|
leaseTimeSeconds |
Duration of DHCP lease in seconds | Option 51 | 3600 |
dnsServers |
List of DNS server IP addresses | Option 6 | None |
timeServers |
List of NTP server IP addresses | Option 42 | None |
interfaceMTU |
MTU size for the interface (doesn't affect switch interfaces) | Option 26 | 9036 |
pxeURL |
PXE boot server URL (TFTP only, no HTTP query strings) | Option 66/67 | None |
disableDefaultRoute |
If true, don't send default route to clients | Option 3 | false |
advertisedRoutes |
Additional static routes | Option 121 | None |
Default Route Behavior
- By default, the DHCP server configures the VPC gateway as the default route
- In L3VNI mode with
disableDefaultRoute: true, routes to other VPC subnets are still sent - Custom routes in
advertisedRoutesare always sent, regardless ofdisableDefaultRoute
Static Leases
Static leases bind specific MAC addresses to predetermined IP addresses. This is useful for:
- Servers requiring consistent IP addresses
- Network equipment that needs fixed IPs
- Hosts that need IPs outside the dynamic range
Configure static leases in the VPC subnet definition:
apiVersion: vpc.githedgehog.com/v1beta1
kind: VPC
metadata:
name: vpc-1
namespace: default
spec:
subnets:
default:
subnet: 10.10.1.0/24
gateway: 10.10.1.1
vlan: 1001
dhcp:
enable: true
range:
start: 10.10.1.10
end: 10.10.1.99
static:
"aa:bb:cc:dd:ee:01":
ip: 10.10.1.5
"aa:bb:cc:dd:ee:02":
ip: 10.10.1.6
"aa:bb:cc:dd:ee:03":
ip: 10.10.1.100
Apply the configuration:
Do Not Edit DHCPSubnet Directly
The VPC is the source of truth for static lease configuration. DHCPSubnet resources are automatically created and managed by the VPC controller. Any changes made directly to DHCPSubnet will be overwritten when the VPC is reconciled.
Managing Static Leases
Adding a Static Lease
To add a new static lease to an existing VPC, edit the VPC YAML:
kubectl get vpc vpc-1 -o yaml > vpc-1.yaml
# Edit vpc-1.yaml to add static lease under spec.subnets.<subnet>.dhcp.static
kubectl apply -f vpc-1.yaml
Alternatively, use kubectl patch on the VPC:
kubectl patch vpc vpc-1 --type=merge -p '
{
"spec": {
"subnets": {
"default": {
"dhcp": {
"static": {
"aa:bb:cc:dd:ee:04": {"ip": "10.10.1.7"}
}
}
}
}
}
}'
Removing a Static Lease
Edit the VPC YAML and remove the MAC address entry from spec.subnets.<subnet>.dhcp.static, then apply.
Changing a Static IP
To change the IP for an existing MAC address, update the VPC configuration and reapply:
kubectl get vpc vpc-1 -o yaml > vpc-1.yaml
# Edit vpc-1.yaml to change the IP for the MAC address
kubectl apply -f vpc-1.yaml
After changing a static IP, the client will need to release and renew its DHCP lease:
Third-Party DHCP Servers
Instead of using the integrated DHCP server, you can configure DHCP relay to use an external DHCP server:
apiVersion: vpc.githedgehog.com/v1beta1
kind: VPC
metadata:
name: vpc-1
namespace: default
spec:
subnets:
default:
subnet: 10.10.1.0/24
gateway: 10.10.1.1
vlan: 1001
dhcp:
relay: 10.99.0.100 # IP of external DHCP server
External DHCP Server Access
The external DHCP server must be reachable from the fabric. Use a StaticExternal connection to provide connectivity to the DHCP server.