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CHAPTER 67
Troubleshooting Bridging and VLAN
Configuration
Troubleshooting Ethernet Switching
MAC Address in the Switch's Ethernet Switching Table Is Not Updated After a MAC Address
Move
Problem
Solution
Copyright © 2010, Juniper Networks, Inc.
Troubleshooting Ethernet Switching on page 1633
Troubleshooting issues for Ethernet switching on EX Series switches:
MAC Address in the Switch's Ethernet Switching Table Is Not Updated After a MAC
Address Move on page 1633
Sometimes a MAC address entry in the switch's Ethernet switching table is not updated
after the device with that MAC address has been moved from one interface to another
on the switch. Typically, the switch does not wait for a MAC address expiration when a
MAC move operation occurs. As soon as the switch detects the MAC address on the new
interface, it immediately updates the table. Many network devices send a gratuitous ARP
packet when switching an IP address from one device to another. The switch updates
its ARP cache table after receipt of such gratuitous ARP messages, and then it also
updates its Ethernet switching table. However, sometimes silent devices, such as SYSLOG
servers or SNMP Trap receivers that receive UDP traffic but do not return
acknowledgement (ACK ) messages to the traffic source, do not send gratuitous ARP
packets when a device moves. If such a move occurs when the system administrator is
not available to explicitly clear the affected interfaces by issuing the
command, the entry for the moved device in the Ethernet
ethernet-switching table
switching table is not updated.
Set up the switch to handle unattended MAC address switchovers.
Reduce the system-wide ARP aging timer. (By default, the ARP aging timer is set at
1.
20 minutes. In Junos OS Release 9.4 and later, the range of the ARP aging timer is
from 1 through 240 minutes.)
[edit system arp]
user@switch# set aging-timer 3
clear
1633
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