What is an IP conflict; how does TR7 check for it?

Short answer

An IP conflict is when the same IP address is defined on two different devices or interfaces on the same network; since both sides reply to ARP requests, traffic sometimes goes to one and sometimes to the other, and connections drop unpredictably (RFC 5227). TR7 performs two checks in its own configuration. If an address that is already defined in the same route table is added again, or if the address of an interface that is moved to another route table exists in the target table, the record is rejected with the IP collision error (IP); since the check is performed within the route table, different route tables can use the same addresses. In a cluster, if a VIP is active on two devices at the same time, the Both VIP is active (red) status appears in the interface list (Interface and IP statuses) and a VIP Status notification is generated. TR7 cannot see a conflict with another device on the network from its configuration; this situation is investigated on the network side.

Where It Is Used in TR7

Where	Field / label	What for
Network → Interfaces → Add IP / Edit IP	IP collision: <ip1>-<ip2> error (IP)	Preventing a duplicate address in the same route table (an address of this device or of the peer device)
Network → Interfaces → Edit Interface → Route Table	IP collision or Route destinations collide error	Preventing address and route collisions while the interface is being moved
Network → Interfaces (in a cluster)	VIP statuses: Both VIP is active (red), Both VIP might be active (yellow/amber) when the peer device cannot be reached	Seeing that the VIP is active (or may be active) on two devices at the same time
Settings → General Settings → Notification Management	Notification Type = VIP Status	Receiving a notification on the VIP … is active for both master and slave event
vService form → frontend row	Port collision: <port> & <other-port> error	Preventing conflicting port usage on the same IP

• Port conflict: What does the configuration error(s) warning in the vService preview (DNS Resolution Error, Port binding error) mean; where does Port Collision appear?

Common Misconceptions

• "TR7 catches all the conflicts on the network." TR7 only prevents duplicates within its own route table and shows when a VIP is active on two TR7 devices at the same time; a conflict with another device is investigated on the network side (the switch's MAC/ARP table, the client's ARP table).
• "The same IP cannot be used in different route tables." Route tables are isolated from one another; the same address can be defined in different route tables.
• "When the vService is deleted, the address is released." The address stays on the interface and keeps replying to ARP; an address that will be moved to another device is first deleted from TR7 or disabled with Disable for (Right-clicking an IP address).

How it is done in the documentation

• Add IP Address · IP
• Interfaces List · Interface and IP Statuses
• Edit Interface · Route Table

Related questions

• What is ARP; how does it relate to VIP failover and the Spoofing setting in TR7?
• What is an IP address; where are IP addresses defined in TR7?
• What does the configuration error(s) warning in the vService preview (DNS Resolution Error, Port binding error) mean; where does Port Collision appear?