Re: Cisco to Juniper switch p2p connectivity with failover

Hello,

I see You haven't actually read the links I supplied. No probs, it happens all the time 

CSCO says

Flex Links are a pair of a Layer 2 interfaces (switch ports or port channels) 

Same for Juniper. The documentation does not spell in clearly but this wording is important

If the active link either goes down or is disabled administratively, it broadcasts a list of 
its known MAC addresses for data traffic; the other link immediately picks up and adds the 
MAC addresses to its address table, becomes active, and begins forwarding traffic.

So You can deduce that the primary link needs to learn MACs for the JNPR RTG to function. And to learn MACs, the link needs to be enabled with "family ethernet-switching". I also verified it in the lab by enabling RTG for et-0/0/15 and et-0/0/16, I also removed "family ethernet-switching" from et-0/0/15|16 and added "family inet" as below:

[edit interfaces et-0/0/15 unit 0]
+      family inet {
+          address 203.0.113.129/30;
+      }
-      family ethernet-switching {
-          vlan {
-              members default;
-          }
-          storm-control default;
-      }
[edit interfaces et-0/0/16 unit 0]
+      family inet {
+          address 203.0.113.133/30;
+      }
-      family ethernet-switching {
-          vlan {
-              members default;
-          }
-          storm-control default;
-      }
[edit protocols rstp]
+   disable;
[edit]
+  switch-options {
+      redundant-trunk-group {
+          group rtg0 {
+              preempt-cutover-timer 60;
+              interface et-0/0/15.0 {
+                  primary;
+              }
+              interface et-0/0/16.0;   
+          }
+      }
+  }

The result is

{master:0}[edit]
ccl@qfx5200# commit ch
01 Feb 2018 10:25:02 UTCeck 
[edit switch-options redundant-trunk-group group rtg0]
  'interface et-0/0/15.0'
    L2ALD rtg : Interface et-0/0/15.0 is not enabled for Ethernet Switching
error: configuration check-out failed

So the conclusion is that You cannot use JNPR RTG as both L2 and L3, only as L2 with "family ethernet-switching". But this does not prevent You from configuring a stub vlan with SVI (IRB or vlan.XYZ L3 interface) and having a L3 connectivity across said link on that stub VLAN.

HTH

Thx
Alex