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Knowledge Base

FAQ-Is the Aging Mechanism of the ARP Table on the SRU Displayed upon the display arp Command Run on the NE40 VRP5.30 Consistent with That on the LPU

Publication Date:  2012-07-27  |   Views:  160  |   Downloads:  0  |   Author:  SU1001731916  |   Document ID:  EKB0000358342


Issue Description

When the display arp command is run on the NE40 VRP5.30, an ARP table containing the VLAN of each LPU is displayed. What is the function of the ARP table? Is the aging mechanism of this table on the SRU consistent with that on the LPU? 

Alarm Information


Handling Process

The ARP entries of the NE40 VRP5.30 are all processed on the LPUs, including learning and aging of ARP entries and sending of ARP request response packets. When ARP is adopted to send packets, the packets are directly sent to the NP by the LPUs.
Under the virtual interface of the VLAN, multiple physical ports exist. In the forwarding process, the 32-bit host route is a must. This 32-bit host route is created after the LPU learns the ARP and reports it to the SRU. Therefore, the ARP entries of the VLANIF interface are saved in the SRU.
After the aging of ARP entries, the LPU deletes the aged entries and reports them to the SRU. However, in the course of processing, information may be lost. In this case, the ARP entries on the SRU become trash. To avoid this from happening, an aging mechanism is configured on the SRU.
No detection packet is sent when the SRU is aging. Detection begins in twice of the aging time. The ARP entries whose aging time is more than twice of the current aging time are deleted. Therefore, the ARP entries on the SRU are detected in 40 minutes. The trash entries, if any, will be deleted. 

Root Cause