Hirschmann GREYHOUND GRS1020, Справочное руководство

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Redundancy
12.6 Link Backup
178
UM Config GRS
Release 8.0 09/2019
12.6 Link Backup
Link Backup provides a redundant link for traffic on Layer 2 devices. When the device detects an
error on the primary link, the device transfers traffic to the backup link. You typically use Link
Backup in service-provider or enterprise networks.
You set up the backup links in pairs, one as a primary and one as a backup. When providing
redundancy for enterprise networks for example, the device lets you set up more than 1 pair. The
maximum number of link backup pairs is: total number of physical ports / 2. Furthermore, when the
state of a port participating in a link backup pair changes, the device sends an SNMP trap.
When configuring link backup pairs, remember the following rules:

A link pair consists of any combination of physical ports. For example, 1 port is a 100 Mbit port
and the other is a 1000 Mbit SFP port.

A specific port is a member of 1 link backup pair at any given time.

Verify that the ports of a link backup pair are members of the same VLAN with the same VLAN
ID. When the primary port or backup port is a member of a VLAN, assign the second port of the
pair to the same VLAN.
The default setting for this function is inactive without any link backup pairs.
Note: Verify that the Spanning Tree Protocol is disabled on the Link Backup ports.
12.6.1 Fail Back Description
Link Backup also lets you set up a Fail Back option. When you activate the fail back function and
the primary link returns to normal operation, the device first blocks traffic on the backup port and
then forwards traffic on the primary port. This process helps protect the device from causing loops
in the network.
When the primary port returns to the link up and active state, the device supports 2 modes of
operation:

When you inactivate Fail back , the primary port remains in the blocking state until the backup link
fails.

When you activate Fail back , and after the Fail back delay [s] timer expires, the primary port returns
to the forwarding state and the backup port changes to down.
In the cases listed above, the port forcing its link to forward traffic, first sends a "flush FDB" packet
to the remote device. The flush packet helps the remote device quickly relearn the MAC addresses.
12.6.2 Example Configuration
In the example network below, you connect ports 2/3 and 2/4 on Switch A to the uplink Switches B
and C. When you set up the ports as a Link Backup pair, 1 of the ports forwards traffic and the other
port is in the blocking mode.
The primary, port 2/3 on Switch A, is the active port and is forwarding traffic to port 1 on Switch B.
Port 2/4 on Switch A is the backup port and is blocking traffic.
When Switch A disables port 2/3 because of a detected error, port 2/4 on Switch A starts
forwarding traffic to port 2 on Switch C.