Static ARP entry on MC-LAG ICL Link in Juniper MX routers

Question

Can someone please explain in detail why we need to setup static arp entry on each MC-LAG peer. This is mentioned below in Juniper Documenttation

https://www.juniper.net/documentation/en_US/junos/topics/concept/mc-lag-feature-concepts.html

Its under topic Virtual Router Redundancy Protocol (VRRP) over IRB and MAC Address Synchronization

If you are using the VRRP over IRB method to enable Layer 3 functionality, you must configure static ARP entries for the IRB interface of the remote MC-LAG peer to allow routing protocols to run over the IRB interfaces. This step is required so you can issue the ping command to reach both the physical IP addresses and virtual IP addresses of the MC-LAG peers.

But why this thing wont work without using static ARP? Can someone please explain this.

Thanks

Answer 1

I can't even tell you how much this requirement frustrated me as well, thank you for asking this one.

Can someone please explain in detail why we need to setup static arp entry on each MC-LAG peer.

The static ARP/ND entries are required because dynamic ARP/ND learning is disabled on the ICL (this is not something you can enable via config).

The good news is that anything running Junos 15.1R3/16.1R1 or higher no longer has this restriction. The documentation is simply out of date, unfortunately.