H3C Technologies H3C S12500-X Series Switches - Manual (Page 12)

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Figure 5 Layer 2 forwarding between sites
Flooding flow
An edge device handles flooding by frame type, as follows:
• Broadcast frame—Floods the frame to all interfaces in the VLAN where the frame has been
received, including internal interfaces and EVI-Link interfaces.
• Destination-unknown unicast or multicast frame—Floods the frame to all internal interfaces in the
VLAN where the frame has been received. The edge device typically does not forward
destination-unknown frames to other sites. If a site-to-site flooding is desirable for a special MAC
address, use the selective flooding feature (see "
Selective flooding ").
To flood a frame to remote sites, an EVI edge device must replicate the frame, encapsulate each replica
in one unicast frame for each destination site, and send the unicast frames to the remote edge devices.
Selective flooding
Selective flooding enables an edge device to send an unknown unicast or multicast frame out of an EVI
tunnel interface.
This feature is designed for special multicast addresses that require flooding across sites but cannot be
added to a multicast forwarding table by IGMP snooping.
For example, you must configure selective flooding for PIM hellos, IGMP general query packets, and
Microsoft NLBS cluster traffic to be sent out of an EVI tunnel interface.