Ethernet Switching
Ethernet Switching

ex4300 VC - can I have two layer 3 interfaces on the same subnet

‎10-24-2016 09:25 PM



I've two circuits from the same VPLS network connected to two ports on a ex4300 VC, both interfaces are layer3 interfaces, but they need to be on the same subnet. 



set unit 0 family inet address 



set unit 0 family inet address 



I want to run eBGP to each one of these IPs through the VPLS network, so if one circuit dies the other one will take over the traffic. So for example ,site A will have two peerings with to the VC switch, one to and one to


Is this possible ?


From a config point of view the switch thinks this is fine but I can't actually test it until I'm on site so I would appreciate your thoughts


I am open to any other suggestions,  please note I can not change the IP subnet for the VPLS as it would require changing multiple sites which is not possible for this maintenance window





Ethernet Switching

Re: ex4300 VC - can I have two layer 3 interfaces on the same subnet

‎10-25-2016 03:56 AM

Never seen this, but not sure why it would not work.  At the same time what most people would do is create a VLAN that contains the 2 interfaces, ge-0/0/1 and ge-1/0/1.  Then associated an [L3] IP address with the VLAN - RVI = Routed VLAN Interface.  For EX4300 this would be via using an IRB - Integrated Routing and Bridging.


Then you create redundancy for the physical links.  For the physical links, now working as L2, versus your previous L3, you need something to break the newly formed L2 loop.  For this you have a few options (in order of my preference):


Make the 2 links into a LAG/AE in which case they load share and provide redundancy BUT you need the SP or VPLS cloud to also support this capability.  For such a connection LACP is generally also used for better link state and failover.


Use RTG at the EX4300.  This option works no matter what the VPLS cloud physical connection is.  This creates active-standby for the 2 links.  For info go here:


Use something ike STP to break the loop.  This assume the VPLS cloud either transparently pass STP BPDU or the cloud connections also run STP.  In the later case, you need to match the cloud STP type with EX4300 configured STP type.  For EX4300 STP info look here:


I would also suggest you upgrade your EX4300 switches to 14.1X53-D40 when it comes out in [hopefully] a few weeks. This would be a generic suggest for anyone using EX4300 switches.  Looking at mid to late November.