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Traffic Loop in Virtual Chassis during network port to VCP(Virtual Chassis Port) port conversion or due to miscabling with EX4200, EX4500 and EX4550 switches

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Article ID: TSB17296 TECHNICAL_BULLETINS Last Updated: 12 Apr 2018Version: 3.0
Alert Type:
PSN - Product Support Notification
Alert Description:
Traffic Loop in Virtual Chassis during network port to VCP(Virtual Chassis Port) port conversion or due to miscabling  with  EX4200, EX4500 and EX4550 switches 
Solution:
If you configure an uplink port as a VCP to create a redundant link with a dedicated VCP connection on  EX4200, EX4500, or EX4550 switches, traffic looping may be seen due to BUM (Broadcast, Unknown, Multicast)  traffic. To avoid traffic looping within the Virtual Chassis, you must reboot the Virtual Chassis after configuring the port conversion and cabling the VCP link.Please refer below link for more details.

https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/virtual-chassis-ex4200-uplink-vcp-cli.html


Additionally, if user mistakenly loops a network port with LLDP enabled on one FPC to a network port with LLDP enabled of another FPC in same Virtual Chassis domain, the ports are partially  converted to VCP due to auto-vcp-conversion feature and traffic looping may be seen. Currently  auto-conversion is default behaviour on   EX4200, EX4500, or EX4550 switches.

PR 1346438 would change this behaviour and will disable default auto-conversion on EX2200, EX3300 EX4200, EX4500 and EX4550 switches.
A new knob, "set virtual-chassis auto-conversion" is introduced to allow users to enable auto-conversion feature. By default this feature will be disabled on  EX2200, EX3300 EX4200, EX4500 and EX4550 switches.

 
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