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VLAN pruning behavior on EX virtual chassis



Article ID: KB30734 KB Last Updated: 04 Mar 2017Version: 2.0

This article describes VLAN pruning behavior on the EX virtual chassis.


How does VLAN pruning work on an EX virtual chassis?


Based on the topology shown below, the EX4500 virtual chassis (VC) is receiving Unknown-Unicast/Multicast/Broadcast traffic on ge-1/0/10 on VLAN 10.

According to hashing, the traffic takes the xe-0/0/0 child member in an aggregated bundle, and ae0 is also part of the same VLAN.

Even after enabling VLAN pruning, the same amount of Unknown-Unicast/Multicast/Broadcast traffic can be seen on one of  the VCP interfaces as well.

The reason for this behavior is as follows. The aggregated link is part of both virtual chassis members, which means the VLAN will be programmed on both members. So when VLAN pruning is enabled on the Broadcast/Multicast/Unknown-Unicast, it will still flood to all the members that are part of that VLAN. However, it will select the optimum path to forward this.

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