3Com CoreBuilder 9000, Руководство пользователя

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398 C
HAPTER
15: LAN E
MULATION
Recovery from Split ELAN
A split ELAN is one in which the secondary LES becomes active along with
the first active LES; the two LESs act to divide the LECs of the ELAN into
two groups, preventing communication between them.
Such a split ELAN can occur, for example, when the location of a link
failure in the network is such that the ATM connection between an active
LES to one LECS is terminated while the connection to another LECS is
not. In addition, the same link failure isolates one LECS from the other. In
this situation, the first LECS decides that the primary active LES has failed
and replaces it with the secondary LES while the second LECS maintains
the primary LES as active.
When the link is repaired, the network recognizes the split ELAN and
recovery occurs automatically as follows: Each LECS now begins receiving
ACTIVE_LES messages from both primary and secondary LESs of the split
ELAN; this tells the LECS that a split ELAN exists. Both LECS act
simultaneously to reestablish the primary LES in the ELAN topology
database as the sole active LES of the ELAN. A message is sent to the
secondary LES instructing it to disconnect all LECs that are attached to it.
When those LECs turn to the LECS to be readmitted to the ELAN, they are
directed to the primary LES and the ELAN is reunited.
Selecting LAN
Emulation
Redundancy Mode
Two types of LAN redundancy are available in the CoreBuilder 9000 ATM
Enterprise Switch: LECS-based LANE redundancy as described previously,
or the NMS-based LANE redundancy, which was the standard prior to
version 4. You can select the type of redundancy through LMA. (For more
information, see “Enable or Disable LE Servers Redundancy” on page
238). If you select LECS-based LANE redundancy the LECS of the switch
must be enabled. The factory default is the NMS-based LANE redundancy.
You verify if the LECS-based LANE redundancy mode is enabled through
the LMA. (See “Display LE Service Redundancy” on page 237).