12-14
C
HAPTER
12: ATM, LAN E
MULATION
,
AND
V
IRTUAL
LAN
S
Aging in the LE_ARP
Cache
As in the transparent bridge FDB, inactive entries in the LE_ARP cache are
removed (aged out). Two LEC parameters are employed for this purpose:
aging-time
and
forward-delay-time
. The parameter used depends on the
way the entry was originally obtained and if the
topology-flag
is set.
When the topology flag is set “on” it means that the network is
undergoing a change in configuration. The following table shows the
conditions under which the appropriate aging parameter is chosen.
Bridge Frame
Forwarding Logic
A bridge processes an Ethernet frame received on a bridge port as
follows:
1
The destination address is looked up in the combined Forwarding
Database.
2
If the destination address is a local station MAC address the frame is
forwarded directly to the bridge port corresponding to the address.
3
If the destination address is found on a remote LEC, the frame is
converted to the standard LAN Emulation format and sent on to the ATM.
4
If the destination address is defined as “self”, this signifies SNMP, CBPDU
frames or any other traffic directed to the bridge software.
5
If the destination address is unknown, the frame is sent to all local bridge
ports. In addition, it is sent to all other members of the ELAN according to
the
unknown unicast flooding mode
(see “Unknown unicast flooding
mode” on page 12-15).
6
Multicast addresses are handled similarly to unknown addresses; they are
flooded.
7
Broadcast frames are sent to the bridge software as well as to all other
ports on the bridge including the ATM.
Table 12-4
Selecting Aging Parameters in the LE_ARP Cache
Entry obtained by
Topology flag
Aged by
Address resolution where address
was registered in LES
Aging-time
Address resolution where address
was not registered in LES, e.g. proxy
LECs
Q
Set
Q
Clear
Forward-delay-time
Aging-time
Address learned from received data
frames
Q
Set
Q
Clear
Forward-delay-time
Aging-time
,
abtthgde.book Page 14 Tuesday, June 23, 1998 10:29 AM
