[j-nsp] ARP Table Timer vs. MAC Table Timer on Juniper

[Karl Gerhard]

Hello

by default
ARP table entries will be saved for 20 minutes and
MAC table entries will be saved for 5minutes.

This seems to be a rather stupid default to me since expired MAC table entries (in conjuction with still existing ARP table entries) will cause Unknown Unicast packets to be flooded. We've been bitten by this because we did VRRP between two routers and two switches and traffic flow was asymmetric so one switch forgot the MAC addresses and flooded Unknown Unicasts.

Is there a logic behind those defaults or am I right to assume that MAC table timers should /always/ be higher than ARP table timers?

Links to the docs:
https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/configuring-arp-aging-timer.html
https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/mac-table-aging-time-bridging.html

Regards
Karl