The DHCP servers that are not active go into "standby" mode; in this mode they regularly get
the current address data and TCU data from the active server so that if the active server fails
a standby server can take over the active role without data loss.
● With the ON_MASTER setting instead of ON_HIGH you can influence the synchronization
in such a manner that the server with the "Master" setting is always the active server (for
this it must be active in the network). This means that in the normal situation
deterministically the same control is always the DHCP server and you can find the actual
address data (/var/etc/udhcp-eth0.leases) and the TCU data (/user/common/tcu/...) there.
ON_MASTER should only be set for a single DHCP server in the system network; there
should not be multiple masters.
● The ON_LOW setting assigns the DHCP server a lower priority than normal. It then
becomes the active server if no server with ON_HIGH or ON_MASTER is found in the
network.
Note
Compatibility with earlier versions
The priority level "ON_LOW" is used automatically if the DHCP server is switched off.
Although such an NCU does have a (standby) DHCP server and keeps a backup of the
lease data, normally, however, it does not become an active server.
InternalDynRangeStart
With the two variables InternalDynRangeStart and InternalDynRangeEnd, you can explicitly
specify the range of IP addresses assigned by the DHCP server. The number range of the
presetting should normally suffice.
Value: IP address
Default: First address in the system network + 10 or +2 (if ≤ 16 addresses)
InternalDynRangeEnd
Value: IP address
Default: Last address in the system network - 15 or -1 (if ≤ 16 addresses)
DHCPDNoMasterWait
If a synchronizing DHCP server has once "detected" a master server in the past, then it waits
for synchronization until the time specified here elapses before it becomes the active server.
This additional pause makes it possible for the intended DHCP master to become the active
DHCP server without displacement even if it is shortly switched on thereafter, or takes longer
to boot than other controls.
Value: Time in seconds
Default: 120
Configuring the system
2.3 Configuration file "basesys.ini"
NCU operating system
20 Commissioning Manual, 12/2017, 6FC5397-1DP40-6BA1
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