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20 Description of the Ring Protocol
20.6 Ring Protocol network design
20.6.1 Using VLAN mappings
(1) VLAN mappings and VLANs for data transfer
When multiple ring IDs are set for a single switch, such as in a multi-ring configuration, the
same VLAN needs to be set multiple times for each ring ID. In such cases, the list of VLANs
used as data transfer VLANs (called VLAN mapping) can be set in advance to simplify data
transfer VLAN settings in a multi-ring configuration, and prevent loops due to mistakes in
configuration settings.
VLAN mappings assign VLANs used for data transfer to VLAN mapping IDs. These VLAN
mapping IDs are set for VLAN groups, and are managed as data transfer VLANs.
Figure 20-28 Example VLAN mapping assignment for each ring
20.6.2 Using forwarding-delay-time for control VLANs
When the Ring Protocol is run from the initial status at switch startup for a transit node, data
transfer VLANs are logically blocked. Transit nodes remove this logical block when they
receive a flush control sent from the master node. However, if the fault monitoring time
(
health-check holdtime
changes for the ring network might not be recognized. In this case, because the logical
block is not released until the reception hold time for flush control frames
(forwarding-shift-time) times out, the data VLAN for the transit node cannot communicate.
Because operation is performed as follows when a forwarding transition time
(forwarding-delay-time) is set for the control VLAN, this kind of case can be avoided.
1.
The transit node performs an immediate logical block of the control VLAN during
switch startup.
2.
Because the control VLAN for the transit node has been logically blocked, a fault is
detected on the master node (even though a fault was already detected previously
upon switch startup). Therefore, communication is switched to an alternate path.
3.
The transit node removes Blocking for the control VLAN, due to a timeout of the
forwarding transition time (forwarding-delay-time) for the control VLAN.
4.
The master node receives a health check frame, detects recovery, and sends a flush
control frame.
5.
The transit node receives this flush control frame, and removes the logical block on
the data transfer VLAN. With this, communication on the data transfer VLAN is
restarted, and restoration of the normal communication path is performed on the
entire ring network.
(1) Relationship between the forwarding transition time for the control VLAN
380
) for the master node is long when the switch is restarted, status
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