"Hardware Resource exhaustion" comes into mind for keeping shorter value for MAC Table. Keeping the value high enough can bite you when there is a flood of traffic from random sources. It can lead to MAC table overruns and could keep the genuine host MAC entries out of MAC table.
I guess many vendors have similar timer strategy. Just configure MAC age timer to be higher than ARP timeout timer. Thanks, On Mon, Dec 11, 2017 at 8:27 AM, Karl Gerhard <karl_g...@gmx.at> wrote: > 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 > > _______________________________________________ > juniper-nsp mailing list juniper-nsp@puck.nether.net > https://puck.nether.net/mailman/listinfo/juniper-nsp > _______________________________________________ juniper-nsp mailing list juniper-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/juniper-nsp