Configuring A Das For Dual Homing - 3Com CoreBuilder 2500 Getting Started Manual

4-20 C 4: C
HAPTER ABLING
FDDI module
(Slot 1)
A
CoreBuilder
2500
B
FDDI
dual
ring
A
CoreBuilder
2500
B
A
Duplex
CoreBuilder
fiber
2500
cable
B
A
CoreBuilder
2500 (DAS)
B
Router
Figure 4-20 Connecting CoreBuilder
Ring (Logical Diagram)
FDDI module
(Slot 2)
A
A
™
CoreBuilder
DAS
6000
B
B
SAS server
A
SAS server
B
(FDDI link)
A
DAS server
B
A A
CoreBuilder
6000
DAS
or
2500
B B
™
Systems to FDDI Dual
Configuring a DAS for Dual Homing
Because a DAS has two attachments to the FDDI
dual ring, A-to-M and B-to-M, it is possible to use
one of them as a "standby" link if the active link
fails. This configuration is called dual homing and is
commonly used for mission-critical devices.
Using dual homing, only one of the two
attachments is active at any given time. In this
sense, a DAS acts as if it is a SAS by using its A port
as a hot standby port. Through SMT, a DAS can be
dual homed to the same concentrator or, more
commonly, to two different concentrators. This
provides a more stable trunk ring of concentrators.
If one concentrator fails, the DAS automatically
enables the standby link to another concentrator to
become the active link. By using dual homing, your
network is more reliable and you can maintain it
more easily. See Figure 4-21.
If the station is a dual path or dual path/dual MAC
station, then the dual-homed station can be
configured in one of two ways:
With both links active
With one link active and one connection withheld
as a backup, only becoming active if one link fails