Manual

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problem, the preemption delay mechanism is imported, and it needs to wait for some times
before the master port preempt the slave port. For keeping the continuance of the flows, the
master port does not process to preempt by default, but turns into the Standby state.
When configuring ULPP, it needs to specify the VLAN which is protected by this ULPP group
through the method of MSTP instances, and ULPP does not provide the protection to other
VLANs.
When the uplink switch is happennig, the primary forwarding entries of the device will not be
applied to new topology in the network. In the figure, SwitchA configures ULPP, the portA1 as
the master port at forwarding state, here the MAC address of PC is learned by Switch D from
portD3. After this, portA1 has the problem, the traffic is switched to portA2 to be forwarded. If
there is the data sent to PC by SwitchD, still the data will be forwarded from portD3, and will be
losed. Therefore, when switching the uplink, the device of configuring ULPP needs to send the
flush packets through the port which is switched to Forwarding state, and update MAC address
tables and ARP tables of other devices in the network. ULPP respectively uses two kinds of
flush packets to update the entries: the updated packets of MAC address and the deleted
packets of ARP.
For making use of the bandwidth resource enough, ULPP can implement VLAN load balance
through the configuration. As the picture illustrated, SwitchA configures two ULPP groups:
portA1 is the master port and portA2 is the slave port in group1, portA2 is the master port and
portA1 is the slave port in group2, the VLANs are protected by group1 and group2, they are 1-
100 and 101-200. Here both portA1 and portA2 at the forwarding state, the master port and
the slave port mutually backup, and respectively forward the packets of the different VLAN
ranges. When portA1 has the problem, the traffic of VLAN 1-200 are forwarded by portA2.
After this, when portA1 is recovering the normal state, portA2 forwards the data of VLAN 101-
200 sequentially, but the data of VLAN 1-100 is switched to portA1 to forward.