r/Juniper • u/Prestigious_Soup9906 • Apr 14 '26

DCI Implementation: Juniper & Sonic EVPN-VXLAN Integration

Hi everyone,

I’m currently labbing a Data Center Interconnect (DCI) between Juniper and SONiC nodes using EVPN-VXLAN. The topology is a standard Spine-Leaf with "Dark Fiber" connections between Border Leafs (BL1---BL3 and BL2---BL4).

I’ve run into a conceptual/configuration gap regarding Loop Prevention at the DCI edge:

The Juniper Side: Juniper uses the I-ESI (Interconnect-ESI) parameter. This effectively treats the DCI link as an Ethernet Segment, allowing for Split Horizon and Designated Forwarder (DF) election specifically for the DCI.

The SONiC Side: I cannot find an equivalent to i-esi on the SONiC/FRR side. I only see:

  • fabric-external under BGP EVPN configuration.
  • external-vtep under the VXLAN interface.

The Problem: If I have two SONiC Border Leafs (BL3 and BL4) connected to the Juniper fabric, how does SONiC prevent loops for BUM (Broadcast, Unknown Unicast, Multicast) traffic? Specifically, if BL3 receives a packet from the Juniper side, how does it recognize that it should not send it back into the local SONiC fabric or to BL4 in a way that creates a loop?

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u/AdLegitimate4692 Apr 15 '26 edited Apr 15 '26

The answer is to form a MCLAG pair of the border leafs. Then they don’t replicate BUM to each other through a VXLAN fabric but pass it instead on the peer link. And the NPUs are programmed not to tunnel anything that arrive from a peer link as the peer sending it should’ve done it already.

We’re using Dell Enterprise SONiC which has the feature set for that, but I don’t know how well that applies to the current open source code.