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# Configuring RSVP MD5 Authentication

RSVP MD5 authentication provides hop-by-hop security against message spoofing and replay attacks. When authentication is configured, RSVP embeds an integrity object within secure cleartext RSVP messages sent between peers. The integrity object includes a key ID unique to the sender, a message sequence number, and keyed message digest. These attributes enable verification of both packet content and sender.

For all potential RSVP peers, you configure the same key on the MPLS neighbor major interfaces, and then enable RSVP authentication on each of these interfaces. When you enable RSVP authentication on an interface, RSVP creates a security association that includes the key, key ID, hash algorithm, and other associated attributes. Each sender and receiver pair maintains the security association for their shared key.

| Note: You must enable authentication on both ends of an RSVP interface to protect the link. Failure to do so can prevent tunnels through the interface from coming up.

Thereafter, RSVP messages sent by a router through the secured interface include an integrity object that contains a key ID for the security association and an MD5 message digest of the message contents. To protect against message replay attacks, the sending interface also places a sequence number in the integrity object. Each sequence number is a unique, monotonically increasing number.

The secured interface expects each received RSVP message to include an integrity object. The interface drops all RSVP messages that do not contain the object.

The receiver uses the key ID and the sender’s address to determine the relevant security association. The key ID is extracted from the received integrity object. The address of the sending interface is extracted from the rsvp_hop object, if present, or from the packet header if the message does not include the rsvp_hop object. The receiver then recomputes the message digest using the association key and algorithm and compares it to the digest received from the peer.

If the digests match, RSVP checks the received sequence number. Every message received from a sender after the first authenticated message must have a sequence number greater than the number from a previously authenticated message from that sender. Messages with invalid sequence numbers are discarded.

If the sequence number is valid, then the RSVP message is authenticated and forwarded for normal RSVP processing. Unauthenticated messages are discarded.

To configure RSVP-TE MD5 authentication:

1. Assign a key to the interface for MD5 authentication between RSVP peers.
   `
   host1(config-if)#mpls rsvp authentication key 34udR973j
   `
2. Enable MD5 authentication on the RSVP-TE interface.
   `
   host1(config-if)#mpls rsvp authentication
   `

To clear the security association on a receiving peer for the specified sending peer:

- Issue the clear mpls rsvp authentication command:
  `
  host1#clear mpls rsvp authentication 10.3.5.1
  `

#### Related Topics

- Basic MPLS Configuration Tasks
- Additional RSVP-TE Configuration Tasks
- clear rsvp authentication
- mpls rsvp authentication
- mpls rsvp authentication key

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