What does Windows error code 13871 (ERROR_IPSEC_IKE_INVALID_HASH_ALG) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: The IKE peer proposed an invalid or unsupported hash algorithm.

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ERROR_IPSEC_IKE_INVALID_HASH	ERROR_IPSEC_IKE_INVALID_HASH_SIZE

ERROR_IPSEC_IKE_INVALID_HASH_ALG

ERROR_IPSEC_IKE_INVALID_HASH_ALG (0x0000362F) The integrity/hash algorithm offered by the peer is not acceptable under the active Windows IPsec policy. This is a proposal-compatibility issue and should be resolved by aligning supported cryptographic suites.

What to check

Compare integrity algorithms on both sides of the IKE policy.
Check whether a security baseline removed legacy algorithms still required by an old peer.
Avoid weakening the Windows policy unless there is a deliberate, risk-reviewed compatibility requirement.

Get-NetIPsecMainModeRule

Microsoft: Get-NetIPsecMainModeRule

Microsoft: Audit IPsec Main Mode

Microsoft: IPsec/IKE system error codes

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