IP : 地址解析服务(ARP)

ARP FAQ :在各自ARP超时超时后,为什么是一些动态ARP条目存在ARP表里?

2016 年 10 月 27 日 - 机器翻译
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简介

本文描述动态地址解析服务(ARP)条目过期。

贡献用米哈拉Stanczyk, Cisco TAC工程师。

在各自ARP超时超时后,为什么是一些动态ARP条目存在ARP表里?

在Cisco IOS软件方面, ARP缓存超时在接口配置模式设置为四个小时(240分钟)默认情况下,但是可以被修改。

输入show interfaces命令为了显示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

在其超时超时以后, ARP条目在ARP缓存实际上存储。在本例中, IP地址10.2.2.2的动态ARP条目是存在ARP缓存253分钟:

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

当创建时,额外时间是抖动被添加到每动态ARP条目。随机的抖动被添加到ARP缓存超时为了避免ARP条目的同步有效期,也许触发ARP风暴。抖动应该是0秒和30分钟范围的一个随机数,与30分钟的最大抖动。

此步骤描述如何确认抖动随机:

  1. 输入detail命令show arp的IP地址为了检查ARP条目详细信息:

    ASR1k#show arp 10.2.2.2 detail
    ARP 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
  2. 清除ARP条目,并且再获取从detail命令show arp的IP地址的输出:

    ASR1k#clear arp 10.2.2.2
    ASR1k#show arp 10.2.2.2 detail
    ARP 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.
    注意计时器重置。

  3. 重复步骤2,并且注意结果不同的:

    ASR1k #clear arp 10.2.2.2
    ASR1k #show arp 10.2.2.2 det
    ARP 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.

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Document ID: 117398