3Com 7600 manual Data Transmission over an Elan, Unknown unicast flooding mode, Mode Bridge action

Data Transmission over an ELAN 12-15

Data Transmission over an ELAN

Unicast Frames When a LEC has established through address resolution that a certain LAN destination corresponds to a certain LEC ATM address, and a data-direct VCC exists to that ATM address, then a data frame addressed to that LAN destination is forwarded via that VCC.

Unknown Unicast When a unicast frame to be transmitted by a LEC has an unknown Frames address, a data-direct VCC is not yet available. In this situation, there are

two possible actions that the LEC can perform, either separately or in combination:

QThe unknown unicast frame can be transmitted over the multicast-send VCC to the BUS. The BUS forwards the frame to all LECs and their attached bridges then flood the frame to all bridge ports to ensure that the frame is received at its destination.

QAddress resolution can be performed continuously on the unknown address until the address becomes known and a VCC can be set up.

Unknown unicast flooding mode

The 7600 Card allows these two actions to be performed in combination according to management selection. The unknown unicast flooding mode allows the user to specify one of the following possibilities for transmitting unknown unicast frames by a bridge:

Table 12-5Unknown Unicast Flooding Mode

Mode	Bridge action
No flooding	No unicast frames are sent to the BUS.
Flooding until ARP	Unicast frames are sent to the BUS until the LE_ARP
Request	request is sent.
Flooding until ARP	Unicast frames are sent to the BUS until the LE_ARP
Response	response is received.

The number of unknown frames sent to the BUS in the time period maximum-unknown-frame-timeis limited by the LEC parameter maximum-unknown-frame-count.