Specifications

ALAXALA Ring Configuration Guide (Edition 1)

3.3.2 Important points on constructing a system

(1) Specify the STP mode on a ring node to allow STP to run on the node and disable STP on the

node if the node does not use STP.

By default, STP by means of PVST+ runs on AX series switches. To change the STP type to Rapid PVST+ or

Rapid (single) STP, specify the applicable mode. Disable STP for ring nodes that do not use STP.

(2) In addition to VLANs for data communication, a ring control VLAN is required.

With the Ring Protocol, a special VLAN is used for controlling the topology of the ring, while normal VLANs

are used for typical data communication. This special VLAN is required per ring (that is, per ring ID). For a

multi-ring configuration, a control VLAN is required for each of the shared link monitoring rings (O-shaped ring)

and shared link non-monitoring rings (C-shaped ring).

Therefore, when you assign VLANs, you need to take the ring control VLAN into account, in addition to the

data communication VLANs.

(3) VLANs for data communication need to be defined in the VLAN mappings.

You need to define data communication VLANs used for the Ring Protocol in the VLAN mappings.

(4) A control VLAN for the virtual link (virtual link VLAN) is also required as a data communication

VLAN.

If you use the Ring Protocol and STP together, you need to configure a virtual link VLAN. You need to

configure a virtual link VLAN as one of the data communication VLANs for all the nodes in the ring network. An

absence or lack of this configuration might lead to false detection of loops, faults, or failures.

Also, a virtual link VLAN does not need to always correspond to a base (virtual link ID). A virtual link VLAN

can contain virtual links for multiple bases.

(5) Configure a virtual link VLAN only for the ring ports on the nodes in the ring.

The virtual link VLAN is used in the ring network. Therefore, you need to configure a virtual link VLAN as

one of the data transfer VLANs for all the nodes in the ring network, but you must not configure a virtual link

VLAN for ports of the nodes in the ring network if the ports use only STP. Loops might occur when a virtual link

VLAN is set for a network controlled by STP.

(6) A VLAN mapping has an only one VLAN when you use PVST+ (including Rapid mode).

When you use the PVST+ STP mode, you must add only one VLAN to the VLAN mapping for a data

communication VLAN used for PVST+. If multiple VLANs are set for a VLAN mapping, PVST+ will not run for

the VLANs. Note that this might lead to a loop.

(7) The failure monitoring time parameter of the Ring Protocol must be less than the BPDU timeout.

As shown in the following formula, you must set the failure monitoring time of health-check frames for the

Ring Protocol (health-check holdtime) to a value less than the timeout detection time for STP BPDUs (hello-time

x 3 seconds).

health-check holdtime [msec] < spanning-tree vlan/single hello-time x 3000 [msec]

When a failure occurs in the ring network, STP detects the BPDU timeout before the Ring Protocol detects the

failure, causing the topology to change and possibly creating a loop.

(8) Any ring node must not have an STP blocking point (non-designated port).

For a node that uses both Ring Protocol and STP, the Ring Protocol takes precedence over STP for the

forwarding/blocking control of the ports. Therefore, even if a port is a non-designated port of STP and blocked

by STP, the port might be determined to be Forwarding in the ring network and treated as a forwarding port,

possibly resulting in a loop of STP.