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ARP age problem

ARP age problem

Created: Dec 30, 2019 02:53:31Latest reply: Dec 30, 2019 03:04:57 576 3 0 0 0
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Hi all.

There is a question about the arp entry. Can you help confirm which options are correct and explain them in detail?

Thanks.


How Are ARP Entries Created, Updated, and Aged?

A. After receiving a gratuitous ARP packet, the device can create or update the ARP entry corresponding to the IP address. 

B. The local device generates or updates the ARP entry of the peer device when receiving an ARP request from the peer device. 

C. The ARP entry of the packet sender is generated or updated when any broadcast ARP request packet is received. 

D. The aging time of dynamic ARP entries can be set. When the aging time expires, the dynamic ARP entries are deleted. 

E. The aging time of dynamic ARP entries can be set. When the aging time expires, the router detects the ARP entries according to the specified probe times. The ARP entries are deleted only when no response is received. 

F. If a service packet sent from an IP address is received, an ARP entry is generated according to the source IP address and source MAC address in the packet. 

G. If a service packet sent from an IP address is received, the ARP entry is updated according to the source IP address and source MAC address in the packet.

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Popeye_Wang
Admin Created Dec 30, 2019 03:04:57

Posted by Sprout at 2019-12-30 02:56 Why are the F and G options wrong?

Hi,

This is because non-ARP packets do not affect ARP entries.

Actually, the description of the E option is not complete. In addition to the detection after the aging time expires, the device also performs detection at 1/2 and 3/4 time. If the device receives a response, it updates the ARP entry. If no response is received, the device performs detection based on the detection interval and the number of detection times when the aging time expires. The device deletes the entry if no response is received.

Therefore, you will find that the actual aging time of ARP entries is longer than the configured value.

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Popeye_Wang
Popeye_Wang Admin Created Dec 30, 2019 02:55:07

Hi Sprout,
I think the right answer is ABCE.
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Sprout
Sprout Created Dec 30, 2019 02:56:30

Posted by Popeye_Wang at 2019-12-30 02:55 Hi Sprout,I think the right answer is ABCE.
Why are the F and G options wrong?
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  • x
  • convention：
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4#
Popeye_Wang
Popeye_Wang Admin Created Dec 30, 2019 03:04:57

Posted by Sprout at 2019-12-30 02:56 Why are the F and G options wrong?

Hi,

This is because non-ARP packets do not affect ARP entries.

Actually, the description of the E option is not complete. In addition to the detection after the aging time expires, the device also performs detection at 1/2 and 3/4 time. If the device receives a response, it updates the ARP entry. If no response is received, the device performs detection based on the detection interval and the number of detection times when the aging time expires. The device deletes the entry if no response is received.

Therefore, you will find that the actual aging time of ARP entries is longer than the configured value.

View more
  • x
  • convention：
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