MAD mechanisms

IRF provides MAD mechanisms by extending LACP and BFD.

You must configure a minimum of one MAD mechanism on an IRF fabric.

Table 1 compares the MAD mechanisms and their application scenarios.

Table 1: Comparison of MAD mechanisms

MAD mechanism	Advantages	Disadvantages	Application scenario
LACP MAD	Detection speed is fast. Does not require MAD-dedicated physical links or Layer 3 interfaces.	Requires an intermediate device that supports extended LACP for MAD.	Link aggregation is used between the IRF fabric and its upstream or downstream device. For information about LACP, see Layer 2—LAN Switching Configuration Guide.
BFD MAD	Detection speed is fast. No intermediate device is required. Intermediate device, if used, can come from any vendor.	Requires MAD dedicated physical links and Layer 3 interfaces, which cannot be used for transmitting user traffic. If no intermediate device is used, any two IRF members must have a BFD MAD link to each other. If an intermediate device is used, every IRF member must have a BFD MAD link to the intermediate device.	No special requirements for network scenarios. If no intermediate device is used, this mechanism is only suitable for IRF fabrics that have a small number of members that are geographically close to one another. For information about BFD, see High Availability Configuration Guide.

MAD mechanism

Advantages

Disadvantages

Application scenario

LACP MAD

Detection speed is fast.
Does not require MAD-dedicated physical links or Layer 3 interfaces.

Requires an intermediate device that supports extended LACP for MAD.

Link aggregation is used between the IRF fabric and its upstream or downstream device.

For information about LACP, see Layer 2—LAN Switching Configuration Guide.

BFD MAD

Detection speed is fast.
No intermediate device is required.
Intermediate device, if used, can come from any vendor.

Requires MAD dedicated physical links and Layer 3 interfaces, which cannot be used for transmitting user traffic.
If no intermediate device is used, any two IRF members must have a BFD MAD link to each other.
If an intermediate device is used, every IRF member must have a BFD MAD link to the intermediate device.

No special requirements for network scenarios.
If no intermediate device is used, this mechanism is only suitable for IRF fabrics that have a small number of members that are geographically close to one another.

For information about BFD, see High Availability Configuration Guide.

LACP MAD

As shown in Figure 6, LACP MAD has the following requirements:

Every IRF member must have a link with an intermediate device.
All the links form a dynamic link aggregation group.
The intermediate device must be a device that supports extended LACP for MAD.

The IRF member devices send extended LACPDUs that convey a domain ID and an active ID. The intermediate device transparently forwards the extended LACPDUs received from one member device to all the other member devices.

If the domain IDs and active IDs sent by all the member devices are the same, the IRF fabric is integrated.
If the extended LACPDUs convey the same domain ID but different active IDs, a split has occurred. LACP MAD handles this situation as described in "Collision handling."

Figure 6: LACP MAD scenario

BFD MAD

BFD MAD can work with or without an intermediate device. Figure 7 shows a typical BFD MAD application scenario.

To use BFD MAD:

Set up dedicated BFD MAD link between each pair of IRF members or between each IRF member and the intermediate device. Do not use the BFD MAD links for any other purposes.
Create a Layer 3 aggregate interface for BFD MAD, and assign a MAD IP address to each member on the aggregate interface.

NOTE:

The MAD IP addresses identify the member devices and must belong to the same subnet.

Assign the ports connected by BFD MAD links to the Layer 3 aggregation group.
On the intermediate device (if any), create a VLAN and assign the ports on BFD MAD links to the VLAN. Do not assign the ports to an aggregate interface.

With BFD MAD, the master attempts to establish BFD sessions with other member devices by using its MAD IP address as the source IP address.

If the IRF fabric is integrated, only the MAD IP address of the master takes effect. The master cannot establish a BFD session with any other member. If you execute the display bfd session command, the state of the BFD sessions is Down.
When the IRF fabric splits, the IP addresses of the masters in the split IRF fabrics take effect. The masters can establish a BFD session. If you execute the display bfd session command, the state of the BFD session between the two devices is Up.

Figure 7: BFD MAD scenario

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