我有一个小型 LAN，其中三个主机 A、B、C 通过交换机连接。如果 A ping B，则 A 和 B 的 arp 表会按预期填充。但是 C 的 arp 表仍然是空的，即使它收到了 arp 广播。这是预期的行为吗？
我认为 arp 广播总是会导致每个主机更新他们的 arp。
假设主机 C 想要 ping 主机 A。因为 C 不知道 A 的 mac 地址，所以它必须发送一个 arp 广播。这似乎有点不必要。如果它第一次知道A的mac-address，它就不需要广播。
谁能解释一下？（如果您能指出验证这一点的官方文件，我会更高兴）
谢谢 ：-）
如果它遵循RFC 826中规定的过程，那么这是预期的行为。主机 C 应仅更新现有条目（如果存在）。如果它是 ARP 请求的目标，它应该只添加一个条目。
从RFC 826，这里是处理流程：
Packet Reception:
-----------------
When an address resolution packet is received, the receiving
Ethernet module gives the packet to the Address Resolution module
*which goes through an algorithm similar to the following.
Negative conditionals indicate an end of processing and a
discarding of the packet.
?Do I have the hardware type in ar$hrd?
Yes: (almost definitely)
[optionally check the hardware length ar$hln]
?Do I speak the protocol in ar$pro?
Yes:
[optionally check the protocol length ar$pln]
Merge_flag := false
If the pair <protocol type, sender protocol address> is
already in my translation table, update the sender
hardware address field of the entry with the new
information in the packet and set Merge_flag to true.
?Am I the target protocol address?
Yes:
If Merge_flag is false, add the triplet <protocol type,
sender protocol address, sender hardware address> to
the translation table.
?Is the opcode ares_op$REQUEST? (NOW look at the opcode!!)
Yes:
Swap hardware and protocol fields, putting the local
hardware and protocol addresses in the sender fields.
Set the ar$op field to ares_op$REPLY
Send the packet to the (new) target hardware address on
the same hardware on which the request was received.