Allied Telesis AT-S63 - Manual (Page 91)

AT-S63 Management Software Menus Interface User’s Guide
Section I: Basic Operations 91
Common VLAN A master switch searches for the other switches in an enhanced stack by
sending out a broadcast packet out a local subnet. (The designation of the
subnet is explained in “Master Switch and Local Interface,” next.) Since a
broadcast packet cannot cross a router or a VLAN boundary, you must
interconnect the switches of a stack with a common VLAN. The VLAN acts
as the transfer path for the broadcast packets from the master switch to
the slave switches and also serves as the path for other management
packets.
Here are several things to keep in mind as you plan the common VLAN of
your enhanced stack:
ˆ Any valid VLAN name and VLAN identifier (VID) can be used for the
common VLAN, but it should be the same on all the switches in the
stack.
ˆ A slave switch of an enhanced stack can be indirectly connected to the
master switch through other switches, provided there is an
uninterrupted path of the common VLAN from the slave switch to the
master switch.
ˆ The Default_VLAN can be used as the common VLAN.
ˆ The common VLAN does not have to be dedicated solely to the
enhanced stacking feature.
For background information on port-based and tagged virtual LANs, refer
to “VLAN Overview” on page 588.
Master Switch
and Local
Interface
Before a switch can function as the master switch of an enhanced stack, it
needs to know which subnet is acting as the common subnet among the
switches in the stack. It uses that information to know which subnet to
send out its broadcast packets and to monitor for the management
packets from the other switches and from remote management
workstations.
Designating the common VLAN and subnet involves creating a routing
interface on the master switch on the common subnet and designating it
as the local interface. The concept of routing interfaces first appeared in
the AT-9400 Series switches with Layer 3 routing and the implementation
of static routing and the Routing Information Protocol (RIP) version 1 and
2.
An interface represents a logical connection to a network or subnet local to
the switch for purposes of routing packets. To configure an interface, you
assign it an IP address and subnet mask appropriate to the subnet where
it will route packets, and add it to the VLAN that contains the subnet.
For the most part, routing interfaces are limited to the IPv4 packet routing
feature and are unnecessary beyond that feature. There are, however, a
few exceptions. One is the enhanced stacking feature. The rule is that the
master switch of an enhanced stack must have at least one interface and