Hirschmann GREYHOUND GRS1020, Справочное руководство

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Specifying the IP parameters
2.7 Management address conflict detection
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UM Config GRS
Release 8.0 09/2019
2.7 Management address conflict detection
You assign an IP address to the device using several different methods. This function helps the
device detect IP address conflicts on a network after boot up and the device also checks
periodically during operation. This function is described in RFC 5227.
When enabled, the device sends an SNMP trap informing you that it detected an IP address
conflict.
The following list contains the default settings for this function:
• Operation : On
• Detection mode : active and passive
• Send periodic ARP probes : marked
• Detection delay [ms] : 200
• Release delay [s] : 15
• Address protections : 3
• Protection interval [ms] : 200
• Send trap : marked
2.7.1 Active and passive detection
Actively checking the network helps prevent the device from connecting to the network with a
duplicate IP address. After connecting the device to a network or after configuring the IP address,
the device immediately checks whether its IP address exists within the network. To check the
network for address conflicts, the device sends 4 ARP probes with the detection delay of 200 ms
into the network. When the IP address exists, the device attemps to return to the previous
configuration, and make another check after the configured release delay time.
When you disable active detection, the device sends 2 gratuitous APR announcements in 2 s
intervals. Using the ARP announcements with passive detection enabled, the device polls the
network to determine whether there is an address conflict. After resolving an address conflict or
after expired release delay time, the device reconnects to the network. Following 10 detected
conflicts, when the configured release delay interval is less than 60 s, the device sets the release
delay interval to 60 s.
After the device performs active detection or you disable the active detection function, with passive
detection enabled the device listens on the network for other devices using the same IP address.
When the device detects a duplicate IP address, it initially defends its address by employing the
ACD mechanism in the passive detection mode and sends out gratuitous ARPs. The number of
protections that the device sends and the protection interval are configurable. To resolve conflicts,
if the remote device remains connected to the network, then the network interface of the local
device disconnects from the network.
When a DHCP server assigns an IP address to the device and an address conflict occurs, the
device returns a DHCP decline message.
The device uses the ARP probe method. This has the following advantages:

ARP caches on other devices remain unchanged

the method is robust through multiple ARP probe transmissions