DHCPv6 Troubleshooting Commands Cisco

DHCPv6 Troubleshooting Commands Cisco

This section explores the methods of DHCPv6 Troubleshooting with Cisco Commands. The problem solving process of DHCPv6 is similar to the resolution of DHCPv4 . Also, due to the number of potentially problematic areas, a systematic approach to problem solving is required, as shown in the following table:

Task No.	Description
Task 1 of troubleshooting:	Resolve address conflicts.
Task 2 of troubleshooting:	Verify physical connectivity.
Task 3 of troubleshooting:	Test with a static IPv6 address.
Task 4 of troubleshooting:	Verify switch port configuration.
Task 5 of troubleshooting:	Test from the same subnet or VLAN.
DHCPv6 Troubleshooting Table.

 Troubleshooting tasks (DHCPv6)

Here are some task and method for DHCPv6  troubleshooting. If you want to learn about DHCPv4 troubleshooting and how to configure DHCPv6 on Cisco, you can following these links:

• Task 1: resolve conflicts

Similar to what happens with IPv4 addresses, leasing an IPv6 address may expire on a client that still needs to connect to the network. The show ipv6 dhcp conflict command   shows all address conflicts that the DHCPv6 server registers with status. If an IPv6 address conflict is detected, the client usually removes the address and generates a new one through SLAAC or with DHCPv6 with status.

• TASK 2: VERIFY THE ALLOCATION METHOD

The  show ipv6 interface interface  command  can be used to verify the address assignment method that appears in the RA message, as indicated by the configuration of the M and O indicators. This information is shown in the last lines of the result. If a client does not receive the IPv6 address information from a DHCPv6 server with status, this could be due to incorrect M and O indicators in the RA message.

• TASK 3: TEST WITH A STATIC IPV6 ADDRESS

By resolving any DHCP problem, whether DHCPv4 or DHCPv6, network connectivity can be verified by configuring a static IP address on a client workstation. In the case of IPv6, if the workstation cannot reach network resources with a statically configured IPv6 address, the root cause of the problem is not SLAAC or DHCPv6. At this point, it is necessary to solve network connectivity problems.

• TASK 4: VERIFY SWITCH PORT CONFIGURATION

If the DHCPv6 client cannot obtain information from a DHCPv6 server, verify that the switch port is enabled and functioning correctly.

• TASK 5: TEST THE OPERATION OF DHCPV6 ON THE SAME SUBNET OR VLAN

If the DHCPv6 server with status or without status is functioning correctly but is located on a VLAN or IPv6 network other than that of the client, it is possible that the problem is the DHCPv6 relay agent. The client that interacts with the interface on the router must be configured with the ipv6 dhcp relay destination command  .

Verification of the router's DHCPv6 configuration

Router configurations for DHCPv6 state and stateless services have many similarities, but also include significant differences. The following are the configuration commands for the two types of DHCPv6 services.

USING DHCPV6 WITH STATUS

Routers configured for DHCPv6 services with status have the address prefix command   to provide addressing information.

R1 (config) # ipv6 unicast-routing
R1 (config) # ipv6 dhcp pool IPV6-STATEFUL
R1 (config-dhcpv6) # address prefix 2001: DB8: CAFE: 1 :: / 64 lifetime 
infinite
R1 (config-dhcpv6) # dns-server 2001: db8: cafe: aaaa :: 5
R1 (config-dhcpv6) # domain-name example.com
R1 (config-dhcpv6) # exit
R1 (config) # interface g0 / 1
R1 (config-if) # ipv6 address 2001: db8: cafe: 1 :: 1/64
R1 (config-if) # ipv6 dhcp server IPV6-STATEFUL
R1 (config-if) # ipv6 nd managed-config-flag

For DHCPv6 services with status, the ipv6 nd managed-config-flag interface configuration mode command is used  . In this case, the client omits the routing information in the RA message and communicates with a DHCPv6 server to obtain addressing information and other information.

USING DHCPV6 WITHOUT STATUS

For stateless DHCPv6 services, the ipv6 nd other-config-flag interface configuration mode command is used  . This informs the device to use SLAAC for addressing information and a stateless DHCPv6 server for other configuration parameters.

R1 (config) # ipv6 unicast-routing
R1 (config) # ipv6 dhcp pool IPV6-STATELESS
R1 (config-dhcpv6) # dns-server 2001: db8: cafe: aaaa :: 5
R1 (config-dhcpv6) # domain-name example.com
R1 (config-dhcpv6) # exit
R1 (config) # interface g0 / 1
R1 (config-if) # ipv6 address 2001: db8: cafe: 1 :: 1/64
R1 (config-if) # ipv6 dhcp server IPV6-STATELESS
R1 (config-if) # ipv6 nd other-config-flag

The show ipv6 interface command   can be used to view the current configuration to determine the allocation method. As shown in the following scheme, the last line of the result indicates the way in which customers obtain addresses and other parameters.
SLAAC

R1 # show ipv6 interface g0 / 1
 GigabitEthernet0 / 1 is up, line protocol is up
 IPv6 is enabled, link-local address is
 FE80 :: D68C: B5FF: DATE: A0C1

DHCP without status

R1 # show ipv6 interface g0 / 1
 GigabitEthernet0 / 1 is up, line protocol is up
 IPv6 is enabled, link-local address is
 FE80 :: D68C: B5FF: DATE: A0C1

DHCP with status

R1 # show ipv6 interface g0 / 1
GigabitEthernet0 / 1 is up, line protocol is up
 IPv6 is enabled, link-local address is 
 FE80 :: D68C: B5FF: DATE: A0C1 

Debugging DHCPv6

When the router is configured as a DHCPv6 server with status or without status, the debug ipv6 dhcp detail command is useful for verifying the reception and transmission of DHCPV6 messages. As shown in the illustration, a DHCPv6 router with status received a REQUEST message from a client. The router uses the addressing information in its IPV6-STATEFUL pool for allocation information.

R1 # debug ipv6 dhcp detail
 IPv6 DHCP debugging is on (detailed)
R1 # 
* Feb 3 21: 27: 41.123: IPv6 DHCP: Received SOLICIT from 
FE80 :: 32F7: DFF: FE25: 2DE1 on GigabitEthernet0 / 1
* Feb 3 21: 27: 41.123: IPv6 DHCP: detailed packet contents
* Feb 3 21: 27: 41.123: src FE80 :: 32F7: DFF: FE25: 2DE1
(GigabitEthernet0 / 1)
* Feb 3 21: 27: 41.127: dst FF02 :: 1: 2
* Feb 3 21: 27: 41.127: type SOLICIT (1), xid 13190645
* Feb 3 21: 27: 41.127: option ELAPSED-TIME (8), len 2
* Feb 3 21: 27: 41.127: elapsed-time 0
* Feb 3 21: 27: 41.127: option CLIENTID (1), len 10
* Feb 3 21: 27: 41,127: 000
* Feb 3 21: 27: 41.127: IPv6 DHCP: Using interface pool IPV6- 
STATEFUL 
* Feb 3 21: 27: 41.127: IPv6 DHCP: Creating binding for 
FE80 :: 32F7: DFF: FE25: 2DE1 in pool IPV6-STATEFUL 
<Se skipped the result>