Address Registration
LE clients register LAN destinations with the LES to ensure uniqueness and to
allow the LES to answer LE_ARP_REQUESTs,which LE clients issue to learn the
ATM address associated with a particular LAN destination. Registrations include the
LAN destination and the ATMaddress that the LE client associates with the LAN
destination. ALAN destination can be either a MAC address or a route descriptor.
Proxy LE clients do not register the MAC addresses of stations on LAN segments
that they are bridging to the ELAN. On the other hand, non-proxy LE clients must
register all the LAN destinations that they represent. All route descriptors must be
registered, regardless of whether they are associated with a proxy or a non-proxy
LE client. Route descriptors are applicable only to proxy LECs that are performing
source route bridging. Aroute descriptor contains the bridge number of the proxy
LE client and the segment number of a ring that the LE client is bridging to that is
equivalent to one hop away.
Address Resolution
LAN communications are based upon source and destination MAC addresses. To
enable such communication on an ATMnetwork, MAC addresses must be resolved
to ATMaddresses. An LE client sends an LE_ARP_REQUEST to the LES to learn
the ATMaddress of a particular LAN destination. If the LAN destination is
registered, the LES responds with the ATMaddress associated with the LAN
destination. Otherwise, the request is forwarded to all proxy LE clients on the
Control Distribute VCC. There is no need to forward the request to non-proxy LECs
because all of their LAN destinations are registered; however, if the LES is
configured to use a single Control Distribute VCC, both proxy and non-proxy LE
clients will receive the request. Control Distribute VCCs provide an efficient way for
the LES to distribute control frames to multiple LE clients.
Proxy LE clients respond to LE_ARP_REQUESTsfor unregistered MAC addresses
that they represent. The LE_ARP_RESPONSE is sent to the LES on the Control
Direct VCC, and the LES forwards the response to the LE client that issued the
request.
Connecting to the BUS
After connecting to the LES, an LE client issues an LE_ARP_REQUEST for the all
1s broadcast MAC address. The LES responds with the ATMaddress of the BUS.
The LE client then initiates the establishment of a Multicast Send VCC to the BUS.
The BUS responds by adding the LE client to the appropriate point-to-multipoint
Multicast Forward VCC. By default, the BUS partitions proxy and non-proxy clients
onto separate Multicast Forward VCCs; however, as was the case with the Control
Distribute VCC, you can configure the BUS to use a single Multicast Forward VCC
for all LE clients. Figure 16on page 266 shows partitioned Multicast Forward VCCs.
Overview of LAN Emulation
Chapter20. Overview of LAN Emulation 265