DHCPv6 Prefix Delegation Configuration
Overview
The prefix delegation feature facilitates the Dynamic Host Control Protocol (DHCP) server capable of assigning prefixes to DHCP clients from a global pool, enabling the Customer Premise Equipment (CPE) to learn the prefix. This feature also supports the DHCP server in assigning multiple prefixes to a single client. The user configures the IPv6 address using the learned prefix on its Local Area Network (LAN) interface with the subnet prefix. The LAN hosts are learning the subnetted prefix through Router Advertisement (RA) messages, an important Neighbor Discovery Protocol (NDP) component, enabling the device to auto-configure the number of IPv6 addresses from 1 to 64.
This feature would enable service providers to assign IP for the CPE that is acting as a router between the service providers' core network and the subscribers' internal network.
Feature Characteristics
• DHCPv6 Identity association for non-temporary addresses (IA_NA) assigns a global IPv6 address on the Wide Area Network (WAN) link. The address comes from a local pool specified in the DHCP Server.
• The Requesting Router (RR) uses the delegated prefix to define the subnet for the LAN based on the prefix received from the DHCP Server.
• The Requesting Router uses the delegated prefix to assign addresses to the LAN devices. The RR can send a Router Advertisement or the devices shall send a Router solicitation.
Benefits
The key benefits are as follows:
• This feature helps the Internet Service Providers (ISPs) to assign the dynamic IPv6 addresses to their customers automatically instead of statically assigning the address.
• This feature adds the capability to get the multiple DHCPv6 prefixes as per the customer requirement.
• This feature allows the centralized management of the IPv6 addresses.
Configuration
This section shows the configuration of the DHCPv6 prefix delegation.
Topology
The requesting router sends the prefix request to the delegating router, which sends the request to the DHCP server. The DHCP server sends the prefix to the requesting router through the delegating router. The IPv6 address is created in the requesting router by combining the prefix learned from the server and the user-defined suffix. The host receives the IPv6 address from the requesting router.
DHCPv6 Prefix Delegation Configuration
Configuring DHCP prefixes
Follow the steps to configure the DHCPv6 prefix delegation.
Configure the Delegating Router:
1. Specify the server interface address connected to the delegating router.
(config)#ipv6 dhcp relay address 2001:101:0:1::131
2. Configure the DHCPv6 up-link interface from the delegating router to the DHCPv6 server using ipv6 dhcp relay uplink command.
(config)#interface ce1/2
(config-if)#ipv6 address 2001:101:0:1::130/64
(config-if)#ipv6 dhcp relay uplink
3. Configure the DHCPv6 down-link interface from the delegating router to the requesting router using ipv6 dhcp relay command.
(config)#interface ce16/1
(config-if)#ipv6 address 3001:101:0:1::135/64
(config-if)#ipv6 dhcp relay
4. Add a static route on the delegating router to reach the host device.
(config)#ipv6 route ::/0 3001:101:0:1::
Configure the Requesting Router device:
1. In the WAN interface, configure the address prefix length option (64). Get the IPv6 address from the server using ipv6 address dhcp command. Enable the requesting router to request the prefix by using ipv6 dhcp prefix-delegation and configure the number of prefixes using ipv6 dhcp client max-delegated-prefixes.
Note: The default value of simultaneous prefixes delegated to a single client is 8.The minimum of simultaneous prefixes delegated to a single client is 1 and the maximum is 64.
Note: If the configured max-delegated-prefix count is greater than 30, then configure the lease times greater than 180 seconds.
(config)#interface ce16/1
(config-if)#ipv6 dhcp address-prefix-len 64
(config-if)#ipv6 address dhcp
(config-if)#ipv6 dhcp prefix-delegation PREFIX_FROM_SERVER
(config-if)#ipv6 dhcp client max-delegated-prefixes 10
2. In the LAN interface, configure the command ipv6 address to create the IPv6 address by using the DHCP prefix learned from the server and user defined suffix.
(config)#interface ce23/1
(config-if)#ipv6 address PREFIX_FROM_SERVER ::1:0:0:0:1/64
3. Add a static route on the requesting router to reach the host device.
(config)#ipv6 route 2001:101:0:1::/64 3001:101:0:1::135
Configure the HOST:
1. In the LAN interface, configure the auto-configuration to get the dynamic IPv6 address from the server.
(config)#interface eth3
(config-if)#ipv6 address autoconfig max-address 10
(config if)#exit
(config)#commit
2. Add a static route on the host to reach the server.
(config)#ipv6 route 2001:101:0:1::/64 3001:101:0:1::135
Running configurations
The running configuration for the Delegating Router is as follows:
#show running-config
!
ipv6 dhcp relay address 2001:101:0:1::131
!
interface ce1/2
ipv6 address 2001:101:0:1::130/64
ipv6 dhcp relay uplink
!
interface ce16/1
ipv6 address 3001:101:0:1::135/64
ipv6 dhcp relay
commit
end
!
The running configuration for the Requesting Router is as follows:
#show running-config
!
interface ce16/1
ipv6 dhcp client max-delegated-prefixes 10
ipv6 address dhcp
ipv6 dhcp address-prefix-len 64
ipv6 dhcp prefix-delegation PREFIX_FROM_SERVER
!
interface ce23/1
ipv6 address PREFIX_FROM_SERVER ::1:0:0:0:1/64
commit
end
!
The running configuration for the HOST is as follows:
#show running-config
!
interface eth3
ipv6 address autoconfig max-address 10
commit
end
!
Validation
Validate the show output after configuration as shown below.
Delegating Router:
#show ipv6 route
IPv6 Routing Table
Codes: K - kernel route, C - connected, S - static, D- DHCP, R - RIP,
O - OSPF, IA - OSPF inter area, E1 - OSPF external type 1,
E2 - OSPF external type 2, E - EVPN N1 - OSPF NSSA external type 1,
N2 - OSPF NSSA external type 2, i - IS-IS, B - BGP,
v - vrf leaked
Timers: Uptime
IP Route Table for VRF "default"
C ::1/128 via ::, lo, 00:03:20
C 2001:101:0:1::/64 via ::, ce1/2, 00:02:58
D 2001:db9:c0f::/48 [80/0] via fe80::eac5:7aff:fe51:723b, ce16/1, 00:00:44
C 3001:101:0:1::/64 via ::, ce16/1, 00:00:50
C fe80::/64 via ::, ce16/1, 00:00:50
#show ipv6 dhcp pd-route
VRF : default
2001:db9:c0a::/48 via 2001:db9:c0b::, ce16/1, (2024-03-07 06:20:43 - 2024-03-07 06:22:13)
2001:db9:c0b::/48 via 2001:db9:c09::, ce16/1, (2024-03-07 06:20:42 - 2024-03-07 06:22:12)
2001:db9:c0c::/48 via 2001:db9:c0d::, ce16/1, (2024-03-07 06:20:39 - 2024-03-07 06:22:09)
2001:db9:c0d::/48 via 2001:db9:c0e::, ce16/1, (2024-03-07 06:20:38 - 2024-03-07 06:22:08)
2001:db9:c0e::/48 via 2001:db9:c0f::, ce16/1, (2024-03-07 06:20:37 - 2024-03-07 06:22:07)
2001:db9:c0f::/48 via fe80::eac5:7aff:fe51:723b, ce16/1, (2024-03-07 06:20:36 - 2024-03-07 06:22:06)
2001:db9:c05::/48 via 2001:db9:c06::, ce16/1, (2024-03-07 06:20:45 - 2024-03-07 06:22:15)
2001:db9:c06::/48 via 2001:db9:c0a::, ce16/1, (2024-03-07 06:20:44 - 2024-03-07 06:22:14)
2001:db9:c08::/48 via 2001:db9:c0c::, ce16/1, (2024-03-07 06:20:40 - 2024-03-07 06:22:10)
2001:db9:c09::/48 via 2001:db9:c08::, ce16/1, (2024-03-07 06:20:41 - 2024-03-07 06:22:11)
#show ipv6 dhcp relay
IPv6 DHCP relay service is Enabled.
VRF Name: default
DHCPv6 Servers configured:
2001:101:0:1::131
DHCPv6 IA_PD Route injection: Enabled
DHCPv6 Duplicate Clients detection: Disabled
Interface Uplink/Downlink
--------- -------------
ce16/1 Downlink
ce1/2 Uplink
Requesting Router:
#show ipv6 dhcp interface
ce16/1 is in client mode
prefix name: PREFIX_FROM_SERVER
learned prefix: 2001:db9:c05::/48
preferred lifetime 0, valid lifetime 60
interfaces using the learned prefix
ce23/1 2001:db9:c0f:1::1
ce23/1 2001:db9:c0e:1::1
ce23/1 2001:db9:c0d:1::1
ce23/1 2001:db9:c0c:1::1
ce23/1 2001:db9:c08:1::1
ce23/1 2001:db9:c09:1::1
ce23/1 2001:db9:c0b:1::1
ce23/1 2001:db9:c0a:1::1
ce23/1 2001:db9:c06:1::1
ce23/1 2001:db9:c05:1::1
#show interface ce23/1
Interface ce23/1
Flexport: Non Control Port (Active)
Hardware is ETH Current HW addr: e8c5.7a51.722e
Physical:e8c5.7a51.722e Logical:(not set)
Forward Error Correction (FEC) configured is Auto (default)
FEC status is N/A
Port Mode is Router
Protected Mode is Promiscuous
Interface index: 10017
Metric 1 mtu 1500 duplex-full link-speed 10g
Debounce timer: disable
ARP ageing timeout 1500
<UP,BROADCAST,RUNNING,ALLMULTI,MULTICAST>
VRF Binding: Not bound
Label switching is disabled
No Virtual Circuit configured
Administrative Group(s): None
Bandwidth 10g
Maximum reservable bandwidth 10g
Available b/w at priority 0 is 10g
Available b/w at priority 1 is 10g
Available b/w at priority 2 is 10g
Available b/w at priority 3 is 10g
Available b/w at priority 4 is 10g
Available b/w at priority 5 is 10g
Available b/w at priority 6 is 10g
Available b/w at priority 7 is 10g
DHCP client is disabled.
Last Flapped: Never
Statistics last cleared: Never
inet6 2001:db9:c05:1::1/64
inet6 2001:db9:c06:1::1/64
inet6 2001:db9:c08:1::1/64
inet6 2001:db9:c09:1::1/64
inet6 2001:db9:c0a:1::1/64
inet6 2001:db9:c0b:1::1/64
inet6 2001:db9:c0c:1::1/64
inet6 2001:db9:c0d:1::1/64
inet6 2001:db9:c0e:1::1/64
inet6 2001:db9:c0f:1::1/64
inet6 fe80::eac5:7aff:fe51:722e/64
ND router advertisements are sent approximately every 561 seconds
ND next router advertisement due in 517 seconds.
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
5 minute input rate 82 bits/sec, 0 packets/sec
5 minute output rate 191 bits/sec, 0 packets/sec
RX
unicast packets 0 multicast packets 25 broadcast packets 0
input packets 25 bytes 2862
jumbo packets 0
undersize 0 oversize 0 CRC 0 fragments 0 jabbers 0
input error 0
input with dribble 0 input discard 0
Rx pause 0
TX
unicast packets 0 multicast packets 38 broadcast packets 0
output packets 38 bytes 5540
jumbo packets 0
output errors 0 collision 0 deferred 0 late collision 0
output discard 0
Tx pause 0
HOST:
#show ipv6 interface eth3 brief
Interface IPv6-Address Admin-Status
eth3 2001:db9:c05:1:923c:b3ff:fe90:9fa9
2001:db9:c06:1:923c:b3ff:fe90:9fa9
2001:db9:c08:1:923c:b3ff:fe90:9fa9
2001:db9:c09:1:923c:b3ff:fe90:9fa9
2001:db9:c0a:1:923c:b3ff:fe90:9fa9
2001:db9:c0b:1:923c:b3ff:fe90:9fa9
2001:db9:c0c:1:923c:b3ff:fe90:9fa9
2001:db9:c0d:1:923c:b3ff:fe90:9fa9
2001:db9:c0e:1:923c:b3ff:fe90:9fa9
2001:db9:c0f:1:923c:b3ff:fe90:9fa9
fe80::923c:b3ff:fe90:9fa9 [up/up]
DHCP Multiple Prefix Delegation Command
The DHCPv6 Prefix Delegation introduces the following configuration command.
ipv6 dhcp client max-delegated-prefixes
Use this command to configure multiple DHCPv6 prefix delegation for a single client.
Command Syntax
ipv6 dhcp client max-delegated-prefixes <1-64>
Parameters
max-delegated-prefixes <1-64> | Specifies the number of prefixes need for a DHCP client. Default number of DHCP prefixes are 8. |
Default
None
Command Mode
Interface mode
Applicability
Introduced in OcNOS version 6.5.1.
Example
This example shows how to configure multiple DHCPv6 prefix delegation for a single client:
RR#configure terminal
RR#(config)#interface ce16/1
RR#(config-if)#ipv6 dhcp address-prefix-len 64
RR#(config-if)#ipv6 address dhcp
RR#(config-if)#ipv6 dhcp prefix-delegation PREFIX_FROM_SERVER
RR#(config-if)#ipv6 dhcp client max-delegated-prefixes 10
RR#(config-if)#exit
RR#(config)#commit
Revised CLI Commands
The following command is revised:
ipv6 address autoconfig
The existing syntax now includes the newly added parameter (max-address <1-64>|). For more details, refer to ipv6 dhcp prefix-delegation command in the DHCPv6 Prefix Delegation Commands chapter in the System Management Guide.
Glossary
The following provides definitions for key terms or abbreviations and their meanings used throughout this document:
Key Terms/Acronym | Description |
Border Network Gateway (BNG) | Border Network Gateway is a critical component in the telecommunication network that serves as the entry and exit point between the ISP and the global network. |
Customer Premises Equipment (CPE) | Customer Premises Equipment is a networking device located on the customer premises. It is present on the edge of the service provider network, which connects the customer devices to the service provider network. |
Delegating Router (DR) | Delegating Router is a network device that delegates the IPv6 address prefixes to the downstream devices. |
Identity association for non-temporary addresses (IA_NA) | Identity association for non-temporary addresses is a unique identifier associated with a set of IPv6 addresses assigned to client devices permanently or for a long time. |
Local Area Network (LAN) | Local Area Network is a network of devices in a small area that may include a building or home. |
Neighbor Discovery Protocol (NDP) | Neighbor Discovery Protocol is a crucial protocol in the IPv6 networks, helping establish the communication and auto-configuration to run the devices in the local network segment seamlessly. |
Neighbor Discovery Router Advertisement (NDRA) | Neighbor Discovery Router Advertisement facilitates a network device to advertise the routing information with the neighboring device so that the neighboring devices take the forwarding decision in dynamic routing. |
Router Advertisement (RA) | Router Advertisement is a critical component in the IPv6 network. The router sends a message to the devices connected to the LAN to communicate its presence and share the configurations with the LAN host. |
Requesting Router (RR) | Requesting Router is a network device that requests the IPv6 address prefixes to the DHCP server to share it with the downstream devices. |
Router Solicitation (RS) | Router Solicitation is a component of the neighbor discovery protocol in the IPv6 network where the host sends a message to discover routers in the local area. When a router receives RS, it responds to the host with RA, which includes the configuration. |
Wide Area Network (WAN) | Wide Area Network refers to large network that includes multiple LANs and spans over a large geographical area. |