ICMP unreachables, code 9,10,13

[Christos Papadopoulos <christos () CS ColoState EDU>]

First, let me thank everyone who responded to my previous
question about routers prioritizing control traffic, your
comments were much appreciated.

My next question is about responses to ICMP pings (echo request),
when they return ICMP UNREACHABLE with codes 9,10 or 13.

These codes are defined as follows:
unreachable     9       Communication with Destination Network
                        is Administratively Prohibited
unreachable     10      Communication with Destination Host
                        is Administratively Prohibited
unreachable     13      Communication Administratively Prohibited
                        - generated if a router cannot forward a packet
                        due to administrative filtering

Responses with these codes seem to imply the presence of a firewall.
Is this assumption correct or are these codes meaningless?

If this a configurable parameter, how to you typically decide what
to set it to?

Thanks!

Christos Papadopoulos
Colorado State University