Intel ER8100STUS - Express 8100 Router, Reference Manual

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Reference.bok : Chapter10 100 Wed Apr 22 10:58:08 1998
100
How Bridging Works
WAN Bridging Services
The Default Action in the central site router is set to
Discard Multicast
, and
the MAC addresses of the remote routers are allowed to pass by filter entries.
This allows necessary remote Multicast packets (using the MAC address of the
router) to be forwarded by the router while all local Multicasts are discarded
without being transmitted on the WAN links.
Typically, the default action of the Destination Forwarding Table is set to Dis-
card to prevent stations that the router does not know about from being Multicast
to all destinations.
Type Forwarding Tables The Type Forwarding Table contains the network access rights for associated
Ethernet packet types. Each entry in the table consist of an Ethernet packet type
code the incoming link and the allowed outgoing link. The known Ethernet Type
Codes are listed in
Appendix C “Ethernet Type Codes”, p. 121 . For example:
Note
For entries in the Type Forwarding Table, the incoming link can only
be
All
when the outgoing link is
None
.
The Type Forwarding Table can only contain static entries defined by the oper-
ator during configuration of the router. Up to 62 entries can be defined.
Default bridge action for
unknown packet types
The bridge can be set up to either forward to all links (default) or discard packets
received for bridging which do not appear in the Type Forwarding Tables. The
bridge then only forwards user-defined Ethernet packet types. This may be done,
for example, for security purposes (to eliminate unauthorized traffic) and for re-
stricting unnecessary or non-essential traffic.
Filtering Function The static entries in the Forwarding Tables can be setup to discard packets, there-
by acting as a filter. To do this, the outgoing link must be defined as
None
(see
above example).
Type Forwarding Table (example)
Ethernet packet Type Incoming Link Outgoing Link
1231 LAN link WAN link 2
1234 WAN link 1 LAN link
1236 WAN link 1 LAN link
AAAA WAN link 2 LAN link
BBBB WAN link 1 WAN link 2
CCCC All None
DDDD All WAN link 1
and so on.