DHCPv6 Prefix Delegation Configuration
Overview
The prefix delegation feature lets a DHCP server assign prefixes chosen from a global pool to DHCP clients, that is how the Customer Premise Equipment (CPE) learns the prefix. The learnt prefix shall be used by the user to configure the IPv6 address on its LAN interface along with the subnet prefix. The LAN hosts are learning the subnetted prefix through router advertisement (NDP protocol) messages, which enables the device to auto-configure its own IPv6 addresses.
This feature would enable service providers to assign IP for the Customer Premise Equipment acting as a router between the service providers core network and subscribers internal network.
Description
• DHCPv6 IA_NA is used to assign a global IPv6 address on the WAN link. The address comes from a local pool specified in DHCP Server.
• The Requesting Router(RR) uses the delegated prefix to define the subnet for the LAN based on the prefix received from DHCP Server.
• The Requesting Router uses the delegated prefix to assign addresses to the LAN devices. Here RR can send Router Advertisement, or the devices shall send Router solicitation.
Acronyms
Field | Description |
|---|---|
IA_NA | Identity association for non-temporary addresses |
NDRA | Neighbor discovery Router Advertisement |
CPE | Customer Premises Equipment |
BNG | Border Network Gateway |
DR | Delegating Router |
RR | Requesting Router |
RA | Router Advertisement |
RS | Router Solicitation |
Topology
.
DHCPv6 Prefix Delegation Configuration
DHCP Relay - Delegating Router (DR)
#configure terminal | Enter configure mode. |
(config)#feature dhcp | Enable the feature DHCP. This is enabled by default. |
(config)#ipv6 dhcp relay | By default, this will be enabled. It starts the IPv6 DHCP relay service. |
(config)#ipv6 dhcp relay address 2001:101:0:1::131 | The relay address configured should be server interface address connected to Delegating Router. |
(config)#interface ce1/2 | Enter interface mode. |
(config-if)#ipv6 address 2001:101:0:1::130/64 | Configure IPv6 address on the interface ce1/2 |
(config-if)#ipv6 dhcp relay uplink | Configure relay uplink on the device connecting the server. |
(config-if)#exit | Exit interface mode. |
(config)#interface ce16/1 | Enter interface mode. |
(config-if)#ipv6 address 3001:101:0:1::135/64 | Configure IPv6 address on the interface ce16/1 |
(config-if)#ipv6 dhcp relay | Relay should be configured on the interface connecting to the client. |
(config-if)#exit | Exit interface mode. |
(config)#ipv6 route 1212:501:102:1::/64 3001:101:0:1::254 | Configure static route towards Host |
Requesting Router (RR)
#configure terminal | Enter configure mode. |
(config)#interface ce16/1 | Enter interface mode. |
(config-if)#ipv6 address dhcp | Configure IPv6 address DHCP. |
(config-if)#ipv6 dhcp prefix-delegation PREFIX_FROM_SERVER | Configure IPv6 DHCP prefix-delegation |
(config-if)#exit | Exit interface mode. |
(config)#interface ce23/1 | Enter interface mode. |
(config-if)#ipv6 address PREFIX_FROM_SERVER ::1:0:0:0:1/64 | Configure IPv6 address from the prefix learnt |
(config-if)#exit | Exit interface mode. |
(config)#ipv6 route 2001:101:0:1::/64 3001:101:0:1::135 | Configure static route towards server |
HOST
#configure terminal | Enter configure mode. |
(config)#interface ce23/1 | Enter interface mode. |
(config-if)#ipv6 address autoconfig | Configure IPv6 autoconfig |
(config if)#exit | Exit interface mode. |
(config)#ipv6 route 2001:101:0:1::/64 fe80::ce37:abff:fec9:7426 ce23/1 | Configure static route towards server |
Linux Host
IPV6_AUTOCONF=yes | IPv6 autoconfig should be set to yes in interface config file. |
DHCP Server
ifconfig eth1 inet6 add 2001:101:0:1::131/64 | Configure IPv6 address on client facing interface |
dhcpd -d -6 -cf /etc/dhcp/dhcpd6.conf eth1 | Start server |
ipv6 route 1212:501:102:1::/64 2001:101:0:1::130 | Configure static route towards Requesting Router |
Sample dhcpd6.conf file
Note: Preferred and Max lifetimes must not be configured with same values.
#
#DHCPv6 Server Configuration file.
#see /usr/share/doc/dhcp*/dhcpd6.conf.sample
#see dhcpd.conf(5) man page
#
preferred-lifetime 200;
default-lease-time 600;
subnet6 2001:101:0:1::/64 {
range6 2001:101:0:1::129 2001:101:0:1::254;
}
subnet6 3001:101:0:1::/64 {
range6 3001:101:0:1::129 3001:101:0:1::254;
prefix6 1212:501:101:: 1212:501:102:: /48;
option dhcp6.name-servers fec0:0:0:1::1;
option dhcp6.domain-search "domain.example";
}
Validation
Delegation Router (DR)
DR#sh 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
Interface Uplink/Downlink
--------- -------------
ce1/2 Uplink
ce16/1 Downlink
Requesting Router (RR)
RR#show ipv6 dhcp interface
ce16/1 is in client mode
prefix name: PREFIX_FROM_SERVER1
learned prefix: 1212:501:102::/48
preferred lifetime 600, valid lifetime 600
interfaces using the learned prefix
ce23/1 1212:501:102:1::1
RR#show int ce23/1
Interface ce23/1
Scope: both
Flexport: Breakout Control Port (Active): Break Out Enabled
Hardware is ETH Current HW addr: cc37.abc9.7426
Physical:cc37.abc9.743f Logical:(not set)
Port Mode is Router
Interface index: 10025
Metric 1 mtu 1500 duplex-full link-speed 1g
Debounce timer: disable
<UP,BROADCAST,RUNNING,MULTICAST>
VRF Binding: Not bound
DHCP client is disabled.
Last Flapped: 2021 Mar 02 09:44:05 (00:03:55 ago)
Statistics last cleared: 2021 Mar 02 09:44:05 (00:03:55 ago)
inet6 1212:501:102:1::1/64
inet6 fe80::ce37:abff:fec9:7426/64
ND router advertisements are sent approximately every 571 seconds
ND next router advertisement due in 434 seconds.
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
5 minute input rate 2 bits/sec, 0 packets/sec
5 minute output rate 23 bits/sec, 0 packets/sec
HOST
[root@localhost ~]#ifconfig -a
eth3 Link encap:Ethernet HWaddr 00:07:E9:A5:23:4C
inet6 addr: 1212:501:102:1:207:e9ff:fea5:234c/64 Scope:Global
inet6 addr: fe80::207:e9ff:fea5:234c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:196985 errors:0 dropped:0 overruns:0 frame:0
TX packets:5733 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:23542362 (22.4 MiB) TX bytes:710558 (693.9 KiB)
Assumptions/Dependencies/Limitations
• Neighbour discovery(NDD module / NSM) sends Router Advertisements (RA) to LAN devices with the learnt prefix, so they can auto-configure the IPV6 addresses for the interface.
• The route has to configure manually on the DR to forward the Traffic from Server to RR
• With Route injection Feature route will be injected in Delegating router, so that the traffic from the DHCP server-side shall be forwarded towards the Requesting router.
• For the Route-injection Feature refer to the DHCPv6 Relay Prefix Delegation Route Injection Configuration section