Bridge Operation - Alcatel speed touch home Advanced User's Manual

Forwarding State
Note
Learning State
Disabled State
14.3.3

Bridge Operation

Learning
Ageing
Flooding
Forwarding
3EC 17096 AAAA TCZZA Ed. 01
Ports exhibit different port states":
If a port is in forwarding state", it participates in the relaying of
frames. In addition, source MAC addresses of frames arriving in
the bridge via this port are stored in the filtering database.
To conserve ADSL bandwidth, only put the ports that are
cross connected in forwarding mode.
If a port is in the learning" state, it only submits information to
the filtering database. It does not participate in the relaying of
frames.
A port in this state, does not participate in the relaying of frames
nor does it update the filtering database.
Ports can be enabled/disabled via the Speed Touch Home web
pages.
If the STHome bridge is active, the filtering database is empty.
Over time it is filled with entries via the Learning mechanism. All
Ethernet frames arriving at ports, are inspected for their source
MAC address, and put into the filtering database along with the
port ID that the frames arrived on.
Entries in the filtering database are removed after a certain time
has elapsed (Ageing Time). This process is referred to as Ageing.
The learning and Ageing process make the Bridge Plug & Play.
Both keep the filtering database up to date with the current
network configuration. E.g. suppose a PC NIC is replaced, the old
MAC address is aged (and will be consequently discarded), while
a new MAC address will be remembered.
If an Ethernet frame arrives, the destination MAC address is
searched in the filtering database. If the destination MAC address
is not found (implying it is currently unknown), it is forwarded to
all ports in the Forwarding state (Flooding), except the one the
frame arrived on.
Broadcast and Multicast MAC addresses are always flooded.
If an Ethernet frame arrives with a destination MAC address that is
found in the filtering database (implying it is currently recognized),
it is forwarded to the port that is associated with that entry. The
difference with flooding is that forwarding is more selective.
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