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300-730 · Question #181

After a network security administrator configures site-to-site IPsec VPN peer, they receive this error message: 1d00h: %CRYPTO-6-IKMP_MODE_FAILURE: Processing of Main Mode failed with peer at…

The correct answer is A. ISAKMP policy must match between sites. The 'Main Mode failed' error indicates IKE Phase 1 negotiation could not complete because the ISAKMP policy parameters - such as encryption algorithm, hash, authentication method, DH group, or lifetime - do not match between the two VPN peers.

Troubleshooting VPNs

Question

After a network security administrator configures site-to-site IPsec VPN peer, they receive this error message: 1d00h: %CRYPTO-6-IKMP_MODE_FAILURE: Processing of Main Mode failed with peer at 150.150.150.1. What is the solution to this problem?

Options

  • AISAKMP policy must match between sites.
  • BIPsec policy must match between sites.
  • CCrypto map must be applied to correct interface.
  • DTransport set must match between sites.

How the community answered

(42 responses)
  • A
    74% (31)
  • B
    17% (7)
  • C
    7% (3)
  • D
    2% (1)

Why each option

The 'Main Mode failed' error indicates IKE Phase 1 negotiation could not complete because the ISAKMP policy parameters - such as encryption algorithm, hash, authentication method, DH group, or lifetime - do not match between the two VPN peers.

AISAKMP policy must match between sites.Correct

IKE Main Mode is the Phase 1 exchange where peers compare ISAKMP policy proposals covering encryption, hashing, authentication, Diffie-Hellman group, and SA lifetime; a mismatch in any of these parameters causes Main Mode to fail, and both routers must have at least one identical ISAKMP policy entry to successfully complete Phase 1.

BIPsec policy must match between sites.

IPsec policy (transform set) mismatches cause IKE Quick Mode (Phase 2) failures, which produce a different error message, not a Main Mode failure.

CCrypto map must be applied to correct interface.

A crypto map not applied to the correct interface means no traffic triggers VPN negotiation at all, but it does not produce a Main Mode processing failure with a specific remote peer address.

DTransport set must match between sites.

'Transport set' is not a standard Cisco IKE or IPsec term; transform set mismatches affect Phase 2 Quick Mode, not Phase 1 Main Mode.

Concept tested: IKE Phase 1 ISAKMP policy parameter matching between peers

Source: https://www.cisco.com/c/en/us/support/docs/security-vpn/ipsec-negotiation-ike-protocols/5409-ipsec-debug-00.html

Topics

#ISAKMP policy#IKE phase 1#Main Mode#site-to-site VPN

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