3Com CoreBuilder 9000, User Manual

Page: 396 / 468

396 C
HAPTER
15: LAN E
MULATION
The LECS has determined that the primary LES, LES 1, is operational by
connecting to it and has assigned it to be the active LES in the ELAN. The
connection has reported 20 LECs attached.
Failure Recovery — Transferring Control to the Redundant LES
A failure of an active LES is sensed by the switch in two steps:
1
The ATM connection between the LECS and the active LES is released.
The release is sent either because of a LES failure or a physical link failure.
2 The LECS fails to reestablish the connection with the LES.
When a connection between active LES and LECS is terminated, the LECS
first responds by assuming that a link between it and the LES is
temporarily down and tries to reestablish the connection. If it is unable to
reestablish the connection, the LECS assumes that the active LES has
failed and declares the secondary LES in the ELAN topology database to
be the active LES. From then on, LECs that request to join the ELAN are
referred to the newly active LES. In this way, LECs that were released from
the failed primary LES are directed by the LECS to the newly active LES
and the ELAN reestablishes itself.