Dual-active detection (DAD)

Hi @LSA,

Dual-active detection (DAD) is a protocol that can detect stack split and dual-active situations and take recovery actions to minimize impact of a stack split on services.

DAD implementation will depend on the platform you're implementing it, for example on CloudEngine 12800 you have the following options:

Direct Mode Through Service Ports

In this mode, DAD is performed through dedicated direct links between member switches, as shown in Figure 1-5.

Figure 1-5 DAD in direct mode through service ports

Proxy Mode Through Eth-Trunk Interfaces

In this mode, DAD detection is performed through an inter-device Eth-Trunk link connected to a relay agent, as shown in Figure 1-6. The DAD proxy function must be enabled on the relay agent.

Compared with the direct mode, the relay mode does not require additional interfaces because the Eth-Trunk interface can perform DAD relay detection while running other services.

Figure 1-6 DAD in reply mode through Eth-Trunk interfaces

DAD Through Management Interfaces

In this mode, links established on management interfaces of the stack member switches are used as DAD links, as shown in Figure 1-7. This mode can be used when all stack member switches connect to the management network through their management interfaces. This mode does not occupy additional ports and does not require a DAD relay agent.

 NOTE:

To implement DAD through management interfaces, ensure that IP addresses are configured for management interfaces.

Figure 1-7 DAD through management interfaces

DAD Through Physical Stack Member Ports (Only Supported on the CE12800&12800E)

In this mode, links established between physical stack member ports of the stack member switches are used as DAD links, as shown in Figure 1-8. This mode uses stack links as DAD links and do not occupy additional ports.

 NOTE:

DAD through physical stack member ports can be used only when the stack is set up through MPU connection.

Figure 1-8 DAD through physical stack member ports

After DAD is configured in a stack, the master switch periodically sends DAD competition packets over the detection links. After the stack splits, the switches exchange DAD competition packets and compare information in the received DAD competition packet with local information. If local information is better, the local switch remains in Active state and continues forwarding service packets. If the received information is better, the switch stack turns to the Recovery state. In this case, all the service interfaces except the excluded ones on the switch are shut down and stop forwarding service packets.

After a stack splits into two stacks, the two stacks compare the following items in the listed order to determine the Active/Recovery state (the election ends when a winning stack is found):

1. Stack priority: The stack to which the switch with the highest stack priority belongs wins.

2. MAC address of switches: The stack to which the switch with the smallest MAC address belongs wins.

After the stack links recover, the two stacks merge into one. The switches in Recovery state restart and restore the shutdown service interfaces. Then the entire stack recovers.

https://support.huawei.com/enterprise/en/doc/EDOC1000177342?section=j009&topicName=dad

You can check the support and specific requirements for your device:

https://support.huawei.com/enterprise/en/doc/EDOC1100127053/fc7b5e2d/stack-support-and-version-requirements

An alternative for DAD in Huawei is MAD, you need to verify if this option is supported on your device:

https://support.huawei.com/enterprise/en/doc/EDOC1000178167/cd86520f/stack-split-and-mad

Hope it helps!

Hi LSA

Stack technology combines multiple switches that are connected through cables into one logical switch .These switches use the same global configuration, IP address and MAC address (stack MAC address) to communicate with other network devices .If a stack cable faulty the communication between these switches may be interrupted and the address conflict between switches  causes a communication failure on the entire network.

Dual-active detection (DAD) is a protocol that can detect stack split and dual-active situations and take recovery actions to minimize impact of a stack split on services.

Two DAD modes are available:

In a stack, you can only configure DAD in direct mode or DAD in relay mode but cannot configure both DAD in direct mode and DAD in relay mode.To ensure DAD reliability, configure four direct links or four relay channels to detect the Eth-Trunk interface. In a dual-active scenario, if one direct link or one relay channel is in Up state, DAD can properly work.

For Loopback DAD negotiation yes they can negotiate so many practice work in that. As best practice in IPv6 Duplicate Address Detection(DAD) comes into play .

Duplicate Address Detection(DAD) IS IPv6 mechanism in which a device checks whether the address to be used for an interface has been used by another interface. IPv6 Loopback Suppression and Duplicate Address Detection (DAD) are discussed in Appendix A of RFC 4862.  That specification mentions a hardware-assisted mechanism to detect looped back DAD messages.  If hardware cannot suppress looped back DAD messages, a software solution is required.  Several service provider communities have expressed a need for automated detection of looped back Neighbor Discovery (ND) messages used by DAD. The rfc7527 includes mitigation techniques and outlines the Enhanced DAD algorithm to automate the detection of looped back IPv6 ND messages used by DAD .For network loopback tests, the Enhanced DAD algorithm allows IPv6 to self-heal after a loopback is placed and removed.