When editing a segment, you have the option to enable Link-Down
Synchronization. Also called Sympathetic HA, this feature allows you to
configure the device to force both ports down on a segment when the device
detects a link state of down on one of the ports. When Link-Down
Synchronization is enabled, the device monitors the link state for both ports
on a segment. If the link goes down on either port, both ports on the segment
are disabled. This functionality propagates the link state across the device.
In the case of Router A and Router B, if the link to router A goes down, then both
ports on the
segment are disabled, resulting in the link to Router B going down, which Router
B
detects. With Link-Down Synchronization, ports respond according to the configured
setting.
The settings include the following:
- Hub — When a port goes down, the system ensures the partner port remains up.
- Breaker — When a port goes down, the system disables the partner port until both ports are manually restarted. The breaker option requires manually restarting both ports.
- Wire — When a port goes down, the system disables the partner port, automatically restarting both ports when the link is re-established.
In addition to the ability to enable Link-Down Synchronization for each
segment, you can change the amount of time after detecting a link is down
before forcing both ports down on a segment. The default is one second. You can
configure the setting to any number of seconds in the range of zero to 240.
After you enable Link-Down Synchronization for a segment, monitoring of
that segment begins only after link up is detected on both ports. When
Link-Down Synchronization disables the ports on a segment, two audit log
messages are generated. The first message in the audit log corresponds to the
port with the link down. The second message corresponds to the segment partner.
Additionally, an error message is added to the system log indicating which port
was detected with the link down, activating Link-Down Synchronization for that
segment.