RFC 4601, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", August 2006

Note: This RFC has been obsoleted by RFC 7761

Note: This RFC has been updated by RFC 5059, RFC 5796, RFC 6226

Errata ID: 1133
Status: Held for Document Update
Type: Technical
Publication Format(s) : TEXT
Reported By: Maren Peasley
Date Reported: 2007-12-21
Held for Document Update by: David Ward
Date Held: 2009-03-22

Section 4.9.2 says:

     Holdtime is the amount of time a receiver must keep the neighbor
     reachable, in seconds.  If the Holdtime is set to '0xffff', the
     receiver of this message never times out the neighbor.  This may be
     used with dial-on-demand links, to avoid keeping the link up with
     periodic Hello messages.

Notes:

Holdtime is tunable by the sender and is required to be kept by the receiver. This coupled with the “infinity” metric 0xffff produces the conditions necessary for a Denial of Service to be possible. This is not addressed in section 6.1.1 (Forged Link-Local Messages) or 6.4 (Denial-of-Service Attacks). Additionally, utilizing AH will not solve this issue as Hello messages instantiate state upon receipt and this state constitutes the “service” that is abused in this form of attack. A tunable option to accept a maximum Holdtime for security purposes would resolve this condition.

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