Configuring Dual-Home Links Dual-Home Link Active-Active
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 10-5
topology change event and the MAC address table is not automatically flushed. This can create stale MAC
address entries that are looking for end devices over the wrong link.
To avoid stale MAC address entries in the forwarding tables of the core switches, some type of
communication needs to occur between the edge uplink switch and the core switches. The DHL Active-
Active feature provides two methods for clearing stale MAC address entries: MVRP Enhanced Operation
or Raw Flooding. Selecting which one of these methods to use is done on a per-DHL session basis.
MVRP Enhanced Operation
The switch uses an enhanced Multiple VLAN Registration Protocol (MVRP) operation to refresh core
MAC address tables as follows:
• For each uplink port, the switch issues joins for each VLAN that is active on that port. This causes the
core switch to only register those VLANs that are active on each link based on the DHL configuration.
• When one of the DHL links fails, the other link issues joins to establish connectivity for the VLANs
that were serviced by the failed link. These new joins contain the “new” flag set, which are forwarded
by the core devices and trigger a flush of the MAC addresses on the core network for the joined
VLANs.
• When a failed DHL link recovers, the link issues new joins to re-establish connectivity for the VLANs
the link was servicing before the link went down. These new joins also trigger a flush of the MAC
addresses on the core network for the joined VLANs.
The switch interacts normally with the core and other devices for MVRP, treating the DHL VLANs on
each uplink port as a fixed registration. This approach requires core devices that support MVRP.
Raw Flooding
When a DHL link fails or recovers and Raw Flooding is enabled for the DHL session, the switch performs
the following tasks to trigger MAC movement:
• Identify a list of MAC addresses within the effected VLANs that were learned on non-DHL ports
(MAC addresses that were reachable through the effected VLANs).
• Create a tagged packet for each of these addresses. The SA for the packet is one of the MAC addresses
from the previously-generated list; the VLAN tag is the resident VLAN for the MAC address; the DA
is set for broadcast (all Fs); the body is just filler.
• Transmit the generated packet once for each VLAN-MAC address combination. These packets are sent
on the link that takes over for the failed link or on a link that has recovered from a failure.
The MAC movement triggered by the Raw Flooding method clears any stale MAC entries. However,
flooded packets are often assigned a low priority and the switch may filter such packets in a highly utilized
network.
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