ARP常见问题：为什么在各自的ARP超时过期后，ARP表中仍然存在一些动态ARP条目？-u17世界杯女足-2014巴西世界杯_世界杯歌曲wakawaka

简介

为什么在各自的ARP超时过期后，ARP表中仍然存在一些动态ARP条目？

相关信息

简介

本文档介绍动态地址解析协议(ARP)条目老化。

为什么在各自的ARP超时过期后，ARP表中仍然存在一些动态ARP条目？

在Cisco IOS®软件中，ARP缓存超时默认设置为四小时（240分钟），但可以在接口配置模式下修改。

输入show interfaces命令以显示ARP缓存超时：

ASR1k#show interfaces gi0/0/2 | include ARP Encapsulation ARPA, loopback not set ARP type: ARPA, ARP Timeout 04:00:00

ARP条目实际存储在ARP缓存中，即使超时已过。在本示例中，IP地址10.2.2.2的动态ARP条目在ARP缓存中已存在253分钟：

ASR1k#show arpProtocol Address Age (min) Hardware Addr Type InterfaceInternet 10.2.2.1 - 30e4.dbb7.7e02 ARPA GigabitEthernet0/0/2Internet 10.2.2.2 253 0004.c01d.7c1a ARPA GigabitEthernet0/0/2

额外时间是创建每个动态ARP条目时添加的抖动。随机抖动会添加到ARP缓存超时，以避免ARP条目同步过期，这可能会触发ARP风暴。抖动应是0秒到30分钟之间的随机数，最大抖动为30分钟。

此过程介绍如何确认抖动是随机的：

输入show arp IP address detail 命令以检查ARP条目详细信息：ASR1k#show arp 10.2.2.2 detailARP entry for 10.2.2.2, link type IP. Dynamic, via GigabitEthernet0/0/2, last updated 253 minutes ago. Encap type is ARPA, hardware address is 0004.c01d.7c1a, 6 bytes long. ARP subblocks: * Dynamic ARP Subblock Entry will be refreshed in 9 minutes and 4 seconds. It has 2 chances to be refreshed before it is purged. Entry is complete. * ARP HA ARP entry is a new entry and has not been synchronized to standby RP. * IP ARP Adjacency Adjacency (for 10.2.2.2 on GigabitEthernet0/0/2) was installed. Connection ID: 0

清除ARP条目，并再次捕获show arp IP address detail命令的输出：ASR1k#clear arp 10.2.2.2ASR1k#show arp 10.2.2.2 detailARP entry for 10.2.2.2, link type IP. Dynamic, via GigabitEthernet0/0/2, last updated 0 minute ago. Encap type is ARPA, hardware address is 0004.c01d.7c1a, 6 bytes long. ARP subblocks: * Dynamic ARP Subblock Entry will be refreshed in 261 minutes and 42 seconds. It has 2 chances to be refreshed before it is purged. Entry is complete.注意计时器已重置。

重复步骤2，注意结果不同：ASR1k #clear arp 10.2.2.2ASR1k #show arp 10.2.2.2 detARP entry for 10.2.2.2, link type IP. Dynamic, via GigabitEthernet0/0/2, last updated 0 minute ago. Encap type is ARPA, hardware address is 0004.c01d.7c1a, 6 bytes long. ARP subblocks: * Dynamic ARP Subblock Entry will be refreshed in 263 minutes and 58 seconds. It has 2 chances to be refreshed before it is purged. Entry is complete.