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Why the redirect packets dropped when next-hop is not available

Created: Apr 10, 2020 01:43:18Latest reply: Apr 10, 2020 01:45:52 250 1 0 0
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Hey there,

The redirection function is configured on the S5720-EI(V200R019C00). According to the documentation: If no ARP entry matches the next hop address on the device, the device triggers ARP learning. If the ARP entry cannot be learned, redirection does not take effect and packets are forwarded along the original forwarding path.

But we find that when the redirected next hop link was disconnected, the packets were not forwarded along the original forwarding path, but dropped in the device, who can explain me the behavior? Thanks.


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Popeye_Wang
Admin Created Apr 10, 2020 01:45:52 Helpful(0) Helpful(0)

Hello,

This is because the function of discarding IP packets that match no routing entry is enabled by default.

On the S5720-EI, S6720-EI, and S6720S-EI, when both the ipv4 destination-unreachable drop command and the traffic policy command are run, both the drop action and the redirection action take effect. The ICMP redirection packets are discarded because the drop action has a higher priority than the redirection action. This leads to a redirection failure for ICMP packets. To make the redirection action for ICMP packets effective, run the undo ipv4 destination-unreachable drop command to disable the drop action. However, disabling the drop action will degrade the attack defense performance of the system. You must configure the two actions properly according to the network requirements.

For details, please refer to https://support.huawei.com/hedex/hdx.do?docid=EDOC1100101074&id=EN-US_CLIREF_0177115162&lang=en

Any further questions, let us know!


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Popeye_Wang
Popeye_Wang Admin Created Apr 10, 2020 01:45:52 Helpful(0) Helpful(0)

Hello,

This is because the function of discarding IP packets that match no routing entry is enabled by default.

On the S5720-EI, S6720-EI, and S6720S-EI, when both the ipv4 destination-unreachable drop command and the traffic policy command are run, both the drop action and the redirection action take effect. The ICMP redirection packets are discarded because the drop action has a higher priority than the redirection action. This leads to a redirection failure for ICMP packets. To make the redirection action for ICMP packets effective, run the undo ipv4 destination-unreachable drop command to disable the drop action. However, disabling the drop action will degrade the attack defense performance of the system. You must configure the two actions properly according to the network requirements.

For details, please refer to https://support.huawei.com/hedex/hdx.do?docid=EDOC1100101074&id=EN-US_CLIREF_0177115162&lang=en

Any further questions, let us know!


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