Intel ER8100STUS - Express 8100 Router, Справочное руководство

Страница: 114 / 150

Reference.bok : Chapter10 102 Wed Apr 22 10:58:08 1998
102
How Bridging Works
WAN Bridging Services
If the packet does not correspond to the entries in any of the Forwarding Tables,
it can be forwarded on all the links except the link from which it was received or
discarded, depending on the configured destination, source and packet type de-
fault bridging function.
Packet processing by
the Destination
Forwarding Tables
Packets which are received for bridging are checked against one of the Destina-
tion Forwarding Tables—packets with Unicast MAC addresses are only checked
against the Unicast Destination Table and packets with Multicast MAC addresses
are checked against the Multicast Destination Table. The process is as follows:
1
If table entries with both the destination MAC address and incoming link
exist, the packet is labelled for forwarding on the outgoing link(s) defined
by these entries. The packet is then passed to the Source Forwarding Table
for further processing.
Note
If a table entry for the packet defines the outgoing link as
None
,
the packet is discarded.
2
If a table entry exists for the Multicast destination MAC address but the
incoming link does not correspond with that of the packet, the packet is dis-
carded.
Note
Unicast destination MAC addresses are allowed from any link.
3 If no entry is found for the destination MAC address and the default action
of the Unicast or Multicast Destination Table (as appropriate) is set to
Dis-
card
, the packet is discarded.
4 If no entry is found for the destination MAC address and the default action
of the Destination Table (Unicast or Multicast as appropriate) is set to pass,
the packet is labelled for forwarding on all the links except the link on
which it was received. The packet is then passed to the Source Forwarding
Table for further processing.
Note
To avoid “storms”, a maximum of 5 packets with unknown Uni-
cast destinations can be forwarded by the router within a 5 sec-
ond period. Additional packets are discarded.