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Both peers establish the MLAG interface interfaces and update the bridge host table over peer ports -port using ICCP (Inter Chassis Control Protocol). RouterOS ICCP does not require an IP configuration, but it should be isolated from the rest of the network using a dedicated untagged VLAN. This untagged VLAN can be configured with vlan-filtering and pvid. Peer ports can also be configured as LACP bonding interfaces.
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in this example, CRS317 and CRS309 devices are used as MLAG peers and any device with two SFP+ interfaces can be used as an LACP client. The SFP+1 interface is used on both peer nodes to create peer-port, and it is used for ICCP, see a network scheme below.
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