Part 2: Implementing DHCPv6 - Stateless DHCPv6

Sivagami Narayanan · ‎10-29-2012

Introduction

This document discuss with an example how to configure stateless DHCPv6 in Cisco IOS routers.Stateless DHCPv6 is one of the most convenient method of implementing DHCPv6 in large networks.Stateless DHCPv6 is a combination of Stateless Address Autoreconfiguration (also known as SLAAC) and DHCPv6. In this one or more IPv6 addresses are assigned to the clients by using SLAAC and additional information i.e configuration parameters such as DNS, NTP are obtained using DHCPv6. This has a significant impact on the DHCP server since the server no longer has to keep track of the state of any assigned IPv6 addresses to the clients. Also there is no need for state refreshment. In case of large networks which has huge number of hosts attached to it, implementing the stateless DHCPv6 will highly reduce the number of DHCPv6 messages that are needed for address state refreshment.

Requirements

Understanding of IPv6 Addressing Scheme
Implementing DHCPv6 - An Introduction

Background

In this configuration example,the router R1 is configured as DHCP server while router R2 is configured as DHCPv6Client.

Note: All configurations are tested in a lab environment involving ASR 1000 series router as DHCP server and Cisco 2800 series router as DHCP Clients.

Topology Diagram

Summary Steps

Server Configuration

In Global Configuration Mode

ipv6 unicast-routing
ipv6 dhcp pool <pool name>
dns-server <specify the dns server address>
domain-name <specify the domain name>
exit

In Interface Configuration Mode

ipv6 address <specify IPv6 Address>
ipv6 nd other-config-flag
ipv6 dhcp server test rapid-commit

Client Configuration

In Global Configuration Mode

enable
configure terminal
ipv6 unicast-routing

In Interface Configuration Mode

ipv6 address autoconfig
ipv6 enable
exit

Configuration

DHCPv6 ServerDHCPv6 Client

!
version 15.1
!
hostname R1
!
ipv6 unicast-routing
ipv6 dhcp pool test
dns-server AAAA:BBBB:10FE:100::15
dns-server 2010:AA01::15
domain-name example.com
!
!
interface GigabitEthernet0/0/1
ipv6 address 2010:AA01:10::2/64
ipv6 nd other-config-flag
ipv6 dhcp server test rapid-commit
!
!
end

!
version 15.0
!
hostname R2
!
ipv6 unicast-routing
ipv6 cef
!
!
interface FastEthernet0/1
ipv6 address autoconfig
ipv6 enable
!
end

Note: Note that in the above configuration, the DHCP server is not configured with any address prefix but only with DNS information. Similarly in the client side is configured to obtain the IPv6 address automatically using the SLAAC.

Verify Commands

debug ipv6 dhcp detail

To display the detailed information about DHCP for IPv6 message decoding use this command. The below output shows the detailed message decoding at the client side.

R2#debug ipv6 dhcp detail
*Oct 29 15:14:03.195: IPv6 DHCP: Sending INFORMATION-REQUEST to FF02::1:2 on FastEthernet0/1
*Oct 29 15:14:03.195: IPv6 DHCP: detailed packet contents
*Oct 29 15:14:03.195:   src FE80::224:14FF:FE57:6451
*Oct 29 15:14:03.195:   dst FF02::1:2 (FastEthernet0/1)
*Oct 29 15:14:03.195:   type INFORMATION-REQUEST(11), xid 5776019
*Oct 29 15:14:03.199:   option ELAPSED-TIME(8), len 2
*Oct 29 15:14:03.199:     elapsed-time 0
*Oct 29 15:14:03.199:   option CLIENTID(1), len 10
*Oct 29 15:14:03.199:     00030001002414576450
*Oct 29 15:14:03.199:   option ORO(6), len 6
*Oct 29 15:14:03.199:     DNS-SERVERS,DOMAIN-LIST,INFO-REFRESH
*Oct 29 15:14:03.199: IPv6 DHCP: DHCPv6 changes state from IDLE to INFORMATION-REQUEST (STATELESS) on FastEthernet0/1
*Oct 29 15:14:03.199: IPv6 DHCP: Received REPLY from FE80::D68C:B5FF:FE2E:E101 on FastEthernet0/1
*Oct 29 15:14:03.203: IPv6 DHCP: detailed packet contents
*Oct 29 15:14:03.203:   src FE80::D68C:B5FF:FE2E:E101 (FastEthernet0/1)
*Oct 29 15:14:03.203:   dst FE80::224:14FF:FE57:6451 (FastEthernet0/1)
*Oct 29 15:14:03.203:   type REPLY(7), xid 5776019
*Oct 29 15:14:03.203:   option SERVERID(2), len 10
*Oct 29 15:14:03.203:     00030001D48CB52EE100
*Oct 29 15:14:03.203:   option CLIENTID(1), len 10
*Oct 29 15:14:03.203:     00030001002414576450
*Oct 29 15:14:03.203:   option DNS-SERVERS(23), len 32
*Oct 29 15:14:03.203:     AAAA:BBBB:10FE:100::15
*Oct 29 15:14:03.203:     2010:AA01::15
*Oct 29 15:14:03.203:   option DOMAIN-LIST(24), len 13
*Oct 29 15:14:03.203:     example.com
*Oct 29 15:14:03.203: IPv6 DHCP: Adding server FE80::D68C:B5FF:FE2E:E101
*Oct 29 15:14:03.203: IPv6 DHCP: Processing options
*Oct 29 15:14:03.203: IPv6 DHCP: Configuring DNS server AAAA:BBBB:10FE:100::15
*Oct 29 15:14:03.203: IPv6 DHCP: Configuring DNS server 2010:AA01::15
*Oct 29 15:14:03.203: IPv6 DHCP: Configuring domain name example.com
*Oct 29 15:14:03.203: IPv6 DHCP: DHCPv6 changes state from INFORMATION-REQUEST to IDLE (REPLY_RECEIVED) on FastEthernet0/1

show ipv6 dhcp interface

This command shows that interface Fa0/0 is configured in client mode and also shows the details of the DNS server address and the domain name that it received from the DHCP server.

R2#show ipv6 dhcp interface
FastEthernet0/1 is in client mode
Prefix State is IDLE (0)
Information refresh timer expires in 23:43:01
Address State is IDLE
List of known servers:
    Reachable via address: FE80::D68C:B5FF:FE2E:E101
    DUID: 00030001D48CB52EE100
    Preference: 0
    Configuration parameters:
      DNS server: AAAA:BBBB:10FE:100::15
      DNS server: 2010:AA01::15
      Domain name: example.com
      Information refresh time: 0
Prefix Rapid-Commit: disabled
Address Rapid-Commit: disabled

show ipv6 dhcp pool

To display the DHCPv6 pool information, in the DHCPv6 server use this command. The output shows that the number of active clients is 1 and also displays other configuration parameter information, such as domain name server address and preferred life time information.

R1#show ipv6 dhcp pool
DHCPv6 pool: test
DNS server: AAAA:BBBB:10FE:100::15
DNS server: 2010:AA01::15
Domain name: example.com
Active clients: 0

Note: In th e above output, the DHCP pool has only the DNS information and there is no IP address assignment.

References

Routing Information Protocol