CHAPTER 61Troubleshooting Bridging and VLANConfiguration• Troubleshooting Ethernet Switching on page 1165Troubleshooting Ethernet SwitchingTroubleshooting issues for Ethernet switching on J-EX Series switches:• MAC Address in the Switch’s Ethernet Switching Table Is Not Updated After a MACAddress Move on page 1165MAC Address in the Switch’s Ethernet Switching Table Is Not Updated After a MAC AddressMoveProblem Sometimes a MAC address entry in the switch’s Ethernet switching table is not updatedafter the device with that MAC address has been moved from one interface to anotheron the switch. Typically, the switch does not wait for a MAC address expiration when aMAC move operation occurs. As soon as the switch detects the MAC address on the newinterface, it immediately updates the table. Many network devices send a gratuitous ARPpacket when switching an IP address from one device to another. The switch updatesits ARP cache table after receipt of such gratuitous ARP messages, and then it alsoupdates its Ethernet switching table. However, sometimes silent devices, such as SYSLOGservers or SNMP Trap receivers that receive UDP traffic but do not returnacknowledgement (ACK ) messages to the traffic source, do not send gratuitous ARPpackets when a device moves. If such a move occurs when the system administrator isnot available to explicitly clear the affected interfaces by issuing the clearethernet-switching table command, the entry for the moved device in the Ethernetswitching table is not updated.Solution Set up the switch to handle unattended MAC address switchovers.1. Reduce the system-wide ARP aging timer. (By default, the ARP aging timer is set at20 minutes. The range of the timer is from 1 through 240 minutes.)[edit system arp]user@switch# set aging-timer 32. Set the MAC aging timer to the same value as the ARP timer. (By default, the MACaging timer is set to 300 seconds. The range is 15 to 1,000,000 seconds.)1165
