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.
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.
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.
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