AT-4016F Installation Manual
9
Bridging
Your AT-4016F acts as a transparent bridge to the Ethernet ports and the
ATM interface. As such, it learns the source MAC address of all incoming
packets and ages out devices which have not been heard for a period of
time.
Bridging involves a forwarding table with a maximum storage capacity of
2,048 MAC address. These addresses are associated with all devices that
have been detected recently either from Ethernet ports or the ATM
interface.
Each virtual LAN uses a unique bridge. Therefore, relayed data within a
virtual LAN is segregated from relayed data in other virtual LANs and
broadcast traffic is isolated within each virtual LAN, even if the virtual
LAN resides in the same AT-4016F.
Since the AT-4016F switch automatically routes traffic onto virtual LANs,
you can only connect virtual LANs either to each other or to external
routers.
Bridge Address
Table
Your AT-4016F checks all incoming packets from each port for their
destination address against a Bridge Address Table. If a packet’s
destination address is not on the same network segment as the originating
packet, the AT-4016F forwards the packet to the network segment
associated with that destination address. However, if the packet’s source
and destination address are on the same network segment, known as local
traffic, the packet is automatically discarded (ignored).
The AT-4016F creates and maintains a dynamic database of addresses
which are stored in a Bridge Address Table. Port information entries in
the Bridge Address Table are, in turn, used as a basis from which to
compare and examine every packet to determine its source address,
segment origin and port information.
If a packet’s MAC address is not already stored in the Bridge Address
Table, the AT-4016F adds the learned address, the associated port number
and a timer value that indicates the age of the dynamic Bridge Address
Table entry. Consequently, the AT-4016F knows the address and
associated port number the next time it sees that address. By using the
information stored in the Bridge Address Table, the AT-4016F is able to
quickly forward each packet to the correct port.
The AT-4016F learns addresses from all packets. When devices are added
to the network, removed from it, or relocated, you do not have to
reconfigure your AT-4016F. Your AT-4016F automatically learns all
addresses.
An address stored in the Bridge Address Table is discarded if there is no
activity from that address after a configured length of time (the default is
five minutes). This aging process ensures that the Bridge Address Table is
not only continually updated but does not grow too large.