Dynamic Host Configuration Protocol (DHCP)

The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on IP networks whereby a DHCP server dynamically assigns an IP address and other network configuration parameters to each device on a network so they can communicate with other IP networks.

The DHCP protocol provides a mechanism for unprovisioned hosts to request an IP-address and configuration via broadcast requests. Based on available address pools, a DHCP server can provide a DHCP client a time-limited IP address “lease”.

When running in a HA configuration with two nodes, only one of the nodes will actively operate as a DHCP server for those intererfaces that are shared between both systems. Client lease information is sychronized between nodes to ensure that upon link or node failure, the newly active DHCP server will operate with the same information.

important

The same interface configured as a DHCP server cannot also be configured for DHCP relay.

Naturally the DHCP server cannot itself reside on an interface that is configured as a DHCP client.

Basic Configuration

A DHCP Server is configured on the network-interface as a host-service of type dhcp-server.

network-interface intf4
name intf4
global-id 4
vlan 4
type external
source-nat false
mtu 9216
address 172.16.4.1
ip-address 172.16.4.1
prefix-length 24
host-service dhcp-server
service-type dhcp-server
server-name 128TDhcpServer4
max-lease-time 10
address-pool 172.16.4.161
start-address 172.16.4.161
domain-server 4.4.4.4
domain-name www.128technology.com
exit
exit
exit
exit

The DHCP server supports setting custom options per dhcp-server instance. Custom options are configured as type-value pairs.

custom 4
code 4
descriptime time-server
value 4.4.4.4
exit

Static reservations are supported. When configuring a static assignment within an address pool, the lease will inherit the attributes of the pool (typically this would be the router and domain-server). If you desire to override any of the attributes of the DHCP pool, these can be configured uniquely per static assignment.

address-pool 192.168.0.20
start-address 192.168.0.20
end-address 192.168.0.200
router 192.168.0.1
domain-server 192.168.0.1
static-assignment 192.168.0.5
address 192.168.0.5
link-layer-address 77:88:CC:00:22:11
domain-server 1.1.1.1
exit
exit

Vendor-Specific Information DHCP Options

Being deployed as a router requires the 128T platform to successfully interoperate with a myriad of network elements. These elements can change from customer to customer and use case to use case. To ensure interoperability between these network elements it can become necessary to support Options and Vendor Extensions on top of base functional support.

The two supported Vendor-Specific Information are:

  1. Vendor-Specific Information Option RFC 2132
  2. Vendor-Identifying Vendor-Specific Information Option RFC 3925

Configuration

Two new configuration objects have added to the dhcp-server object: vendor-specific-information and vendor-indentifying-vendor-specific-information.

An example vendor-specific-information DHCP option is shown below:

  • Code 72, AP Controller Type
network-interface dhcp-server-intf
name dhcp-server-intf
...
address 192.168.1.1
...
host-service dhcp-server
service-type dhcp-server
server-name my-dhcp-server
max-lease-time 3600
address-pool 192.168.1.100
...
vendor-specific-information 72
code 72
description AP Controller Type
value 1
encoded-type uint8
quantity singular
exit
...
exit
exit
exit
exit

An example of two vendor-identifying vendor-specific information DHCP options are shown below:

  • Code 72, Enterprise-Number 122 (SONY), PS Server Addresses
  • Code 72, Enterprise-Number 311 (Microsoft), Enable/Disable xBox Live
network-interface dhcp-server-intf
name dhcp-server-intf
...
address 192.168.1.1
...
host-service dhcp-server
service-type dhcp-server
server-name my-dhcp-server
max-lease-time 3600
address-pool 192.168.1.100
...
vendor-identifying-vendor-specific-information 122 72
description AP Controller addresses
code 72
enterprise-number 122
description PS Server Addresses
value 10.1.1.1
value 10.1.1.2
encoded-type ipv4-address
quantity array
exit
vendor-identifying-vendor-specific-information 311 72
description AP Controller addresses
code 72
enterprise-number 311
description Enable/Disable xBox Live
value false
encoded-type boolean
quantity singular
exit
...
exit
exit
exit
exit

Troubleshooting

From within the PCLI, you can execute show network-interface application to show statistics related to the DHCP server as well as any active DHCP client leases.

admin@gouda.novigrad# show network-interface application
Tue 2020-04-21 15:26:19 UTC
====================================================================================================
Application Data
====================================================================================================
Interface: gouda:wan-interface
state: Interface not configured for any managed application
Interface: gouda:lan-interface
dhcp-server:
kea-status:
active (running/success) since Sat 2020-04-11 12:57:23 UTC
kea-ctrl-status:
active (running/success) since Sat 2020-04-11 12:57:23 UTC
metrics:
declined-addresses: 0
pkt4-ack-sent: 1900
pkt4-discover-received: 403
pkt4-inform-received: 469
pkt4-offer-sent: 403
pkt4-received: 2317
pkt4-release-received: 2
pkt4-request-received: 1443
pkt4-sent: 2303
reclaimed-declined-addresses: 0
reclaimed-leases: 13
subnet[1].assigned-addresses: 24
subnet[1].declined-addresses: 0
subnet[1].reclaimed-declined-addresses:0
subnet[1].reclaimed-leases: 13
subnet[1].total-addresses: 181
subnets:
subnet:
current-lease-count: 24
current-leases:
lease:
client-last-transaction-time: 2020-04-21 15:26:12
hostname: homecomtsiphone
hw-address: 70:3c:69:58:01:28
ip-address: 192.168.0.36
valid-lifetime: 86400
subnet: 192.168.0.1/24
...
ha-heartbeat:
role: primary
state: standalone
Interface: gouda:lan-untrusted
state: Interface not configured for any managed application
Interface: gouda:mgmt-interface
state: Interface not configured for any managed application
Completed in 0.76 seconds

Active client lease management can be seen in the GUI by navigating to Router > Node > DHCP Server. It is also from within this interface that you can selectively revoke a client lease. config_dhcp_1

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