ICMP Blocked Notification

Document Type Expired Internet-Draft (individual)
Author Eliot Lear 
Last updated 2000-08-21
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


Since the introduction of private addresses[1] the use of NATs and firewalls has introduced not only inability to communicate using certain mechanisms, such as AH[2], ESP[3], and H.323[4], but also difficulty in determining the reason for the failed communication. This document specifies methods an intermediate device such as a router, a firewall, or a NAT may use to inform end hosts that a particular type of communication is not possible. It also recommends practices for both the frequency of transmission of such error notices, and their consumption by the end hosts. This document is an outgrowth of the 'foglamps' discussion that occurred within the IETF between late 1999 and 2000, and is not the product of a working group.


Eliot Lear (lear@cisco.com)

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)