3.1.b (viii) Stateful, stateless DHCPv6

3.1.b (viii) Stateful, stateless DHCPv6


SLAAC and DHCPv6 can go hand in hand because SLAAC does not disseminate other information like DNS or other DHCP options.
These are things that we no longer necessarily have to track so they can be stateless. However they still require a DHCPv6 server for.

For example here’s a config of DHCPv6 just for domain and dns, which is a common configuration you might implement.

conf t
ipv6 dhcp pool DHCPPOOL
dns-server 2000::9999:1
domain-name mydomain.com

interface GigabitEthernet0/0
ipv6 address 2000::9999:1/64
ipv6 nd other-config-flag
ipv6 dhcp server DHCPPOOL

SLAAC will give us the address, while DHCPv6 will give us the domain info.

We can use the other-config-flag or the managed-config-flag

In the above example we used the other-config-flag in our configuration, this tells the host use the DHCPv6 server only for dhcp options, but not the IP.

Managed-config-flag tells the host to use the DHCPv6 server for both addressing and options.

So now what happens when a host comes on the network?

Here is the process:
1. The host will send out a router solicitation
2. R1 will respond with a router advertisement indicating the flags (other configuration) and the prefix to use via SLAAC
3. The host will utilize SLAAC for the address and then initiate another proceess for the DHCPv6 DNS options

Here is the flag in the Router advertisement from R1 to the client

img 5ac0252069e64

Here is the bottom of the same packet telling him what prefix to use

img 5ac02524de26f

Now the client will send out a DHPc6 request for DNS


img 5ac0252a5fcd0

Finally R1 will reply with DNS info


img 5ac0252f16e83


Of course we can use DHCPv6 to distribute and track everything, here’s how that’s configured on a Cisco router:

conf t
ipv6 dhcp pool DHCPPOOL
address prefix 2000:9999::/64 lifetime infinite infinite
link-address 2000:9999::227:56FF:FE35:F601/64
dns-server 2000:9999::227:56FF:FE35:F601
domain-name mylab.com

int g0/1
ipv6 dhcp server DHCPPOOL
ipv6 add 2000:9999::/64 eui-64
no shut

The client connected to the lan then just needs:

int g0/1
ipv6 address dhcp
ipv6 enable

As described in 3.1.b (vi) then the DHCPv6 process starts which is : solicit, advertise, request, reply


img 5ac02535cb131

Some verification commands for IPv6 DHCP include:

A general overview of the DHCP config:

show ipv6 dhcp pool <poolname>

img 5ac0253d90dfc

Information about each DHCP client:

show ipv6 dhcp binding


img 5ac02542b401b


Leave a comment