Address Resolution; Data-Direct Vcc; Vcc To Bus; Configuring Les Le_Arp Policies - 3Com CoreBuilder 9000 User Manual

388 C 15: LAN E
HAPTER

Address Resolution

Data-direct VCC

VCC to BUS

Configuring LES
LE_ARP Policies
MULATION
When a LEC needs to forward a unicast data frame whose LAN
destination is not found in its local Forwarding Data Base, it attempts to
locate a LEC that represents the LAN destination on the ATM network. To
do this, it turns to the LES in a process called address resolution.
As mentioned previously, the LES is the central "directory" service for
verifying LEC ATM addresses on an ELAN. (See "LAN Emulation Server"
on page 376.) The LEC submits an LE_ARP (LE Address Resolution
Protocol) Request to the LES. If a LEC ATM address that corresponds to
the submitted LAN destination is found in the LES table, it is transmitted
back to the requesting LEC as an LE_ARP Response. In case the requested
address is not found at the LES, the LES forwards the query to other LECs
to search the non-registered addresses and then return a positive
response back to the requesting LEC. On receipt of an LE_ARP Response,
the LEC records the destination LEC ATM address together with the LAN
destination in its FDB ARP-cache. The way that the LES handles LE_ARP
requests can be configured by management. (See "Configuring LES
LE_ARP Policies" on page 388.)
On receipt of the destination LEC address, the transmitting LEC
establishes a data-direct VCC for direct communication across the ATM
network to the destination LEC if one does not already exist.
In a similar way, the LEC uses address resolution during initialization to
ascertain the ATM address of the BUS. When the ATM address of the BUS
is known, the multicast-send and multicast-forward VCCs are established
between LEC and BUS and any unknown unicast, multicast, or broadcast
messages are sent on it.
The way in which the LES handles LE_ARP requests from a LEC can be
configured by management. Each LES in the CoreBuilder switch can be
configured independently. Three such policies can be set:


LE_ARP Response Policy


ELAN Response Policy


LE_ARP Response Policy for Route Descriptors