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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.
Figure 56-2: VLAN load balance
56-21
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Troubleshooting
