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Managing Serviceguard Fifteenth Edition > Appendix H IPv6 Network Support

IPv6 Relocatable Address and Duplicate Address Detection Feature


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The IPv6 networking stack has a new feature, Duplicate Address Detection (DAD), that was not previously available in IPv4. When an address is being added, the DAD detects a duplicate address that is already being used on the network. It sends out a multicast message to the network neighborhood, and requires at least one second to listen for responses from other nodes. If no responses are received in that time, the relocatable IPv6 address is considered free to use. For more information regarding this feature, please refer to the RFC 2462.

The effect of this feature on Serviceguard is that the time required to add each IPv6 relocatable address will be at least one second longer than adding a corresponding IPv4 address. Depending on the number of IPv6 addresses configured within a package, this could have a moderate to significant impact on package start time.

If you do not need duplicate address detection, you can disable the DAD feature by setting the kernel parameter ip6_nd_dad_solicity_count to 0. Please note that this kernel parameter applies to the entire system. If you turn it off, you disable it for all applications on the system. For systems where DAD is not required, disabling this feature can significantly improve the start time of package packages containing a large number of IPv6 relocatable addresses.

To determine the current state of DAD on your system, use the ndd -get command to see the current value of the kernel parameter.

# ndd -get /dev/ip6 ip6_nd_dad_solicit_count

If the result is 1, the feature is turned on. If the result is 0, the feature is turned off.To temporarily change the state of DAD on your computer, use the ndd -set command to change the kernel parameter.

# ndd -set /dev/ip6 ip6_nd_dad_solicit_count n

where n is a number: either 1 to turn the feature on, or 0 to turn it off.

To change the state of DAD on your computer so that it will remain changed even after a reboot, add the following entries to the /etc/rc/config.d/nddconf file:

# TRANSPORT_NAME[index]=ip6

# NDD_NAME[index]=ip6_nd_dad_solicit_count

# NDD_VALUE[index]=n

Where index is the next available integer value of the nddconf file, and n is a number: either 1 to turn the feature ON or 0 to turn it OFF.

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