# Configuring LDP MD5 Authentication

LDP MD5 authentication provides protection against spoofed TCP segments that can be introduced into the connection streams for LDP sessions. Authentication is configurable for both directly connected and targeted peers.

You configure a shared secret (password) on potential LDP peers. Any given pair of peers must share the same password. When a peer sends a TCP segment to an LSR, it uses the password and the segment to compute an MD5 digest that it sends along with the segment.

When the LSR receives the segment, the LSR calculates its own version of the digest using its instance of the password and the segment. The LSR validates the segment if the local digest matches the received digest. If the comparison fails—for example, if the password is not configured the same on both peers—the LSR drops the segment and does not send a response to the peer.

You can optionally enable a strict authentication mode that allows only peers configured with passwords to establish sessions. In this mode, LDP hello messages from peers that have no password are ignored. If you do not configure strict authentication, then peers that do not have configured passwords can establish connections with each other.

If you configure LDP MD5 authentication or change the authentication password for a peer while it is in an established LDP session, MPLS restarts that session.

To configure LDP MD5 authentication:

1. Set the password for an LDP peer.
   host1(config)#mpls ldp neighbor 10.3.5.1 password rop23ers
2. (Optional) Set strict LDP authentication mode so that only peers with passwords can establish LDP sessions.
   host1(config)#mpls ldp strict-security

#### Related Topics

- Basic MPLS Configuration Tasks
- Additional LDP Configuration Tasks
- mpls ldp neighbor password
- mpls ldp strict-security