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Routing & Switching · Intermediate

OSPF Authentication

Methods for authenticating OSPF packets: null, plaintext, MD5 and HMAC-SHA with key chains.

Definition

OSPFv2 supports type 0 (none), type 1 (simple password) and type 2 (cryptographic: MD5 or HMAC-SHA per RFC 5709). It can be configured per area or per interface, and keys must match. OSPFv3 uses IPsec or the RFC 7166 authentication trailer.

Example

ip ospf authentication message-digest ; ip ospf message-digest-key 1 md5 S3cret

Exam tip

Authentication mismatch stops neighbors forming; debug ip ospf adj shows 'Mismatched Authentication type'.

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