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Multiple independent control planes control neighboring sections of network in a multi-domain setting. These scenarios differ from the network islands in the previous section, which are controlled by one logical control plane. In this case, a controller might receive receive probes that have originated outside of its domain. These probes mark network edge links. 

A problematic case involves probes from outside devices whose ID(s) are found within the domain (ID aliasing). Other than under special circumstances (e.g. the probe arrives before the domain's own device is discovered, or the recipient of the probe is the one being aliased), ID aliasing is difficult to detect, and leads to wrongly reported links.

ONOS employs per-logical instance fingerprints to identify its own cluster. Since ONOS 1.4, the ability to add fingerprint information to probe messages has been added to the LLDPLinkProvider, to aid in the identification of foreign devices and ID aliasing.

Host Discovery

The Device Subsystem discovers network end-hosts via ARP and DHCP messages detected as PacketIns, and describes their locations in the network in terms of Device-Port pairs referred to as ConnectPoints. The HostLocationProvider implements this function by implementing a DeviceListener in a similar vein as the LLDPLinkProvider.

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