3Com CoreBuilder 7000, Operation Manual

Page: 157 / 264

LAN Emulation Redundancy 157
Figure 51 ATM Connections between LECS and LES
If the primary LES for an ELAN is marked operational, the LECS assigns it
as the active LES and the secondary as the redundant LES, otherwise the
secondary LES is assigned as active. If both primary and secondary LESes
are not operational, an error message is returned to any LEC requesting
to join the ELAN.
Assuming that the required network connectivity exists, all LECS make
the same choices for active and redundant LESes for each ELAN in their
(identical) topology databases so that every LECS has the same picture of
the network topology.
Verifying the Active Status of a LES
To resolve a split ELAN, as described below, the LECS needs to know if a
LES actually has LECs attached to it. This information is transmitted by the
LES to the LECS over the same ATM connection which was established by
the LECS to it. A LES with LECs connected to it periodically transmits an
ACTIVE_LES message, containing the number of its LECs, to all LECS that
are connected to it. If an active LES has no LECs associated with it, it does
not send an ACTIVE_LES message.
Table 42 shows the LES information for an ELAN in the LECS topology
base.
L ECS 2 L ECS 4
L ECS 3 L ECS 5
L ECS 1
EL AN
Prim ar y
L ES
Se co nda ry
L ES
AT M Co nnec tio ns