> Paul,
>
> Thanks for your reply. How about helping me with this one:
>
> When are ICMP redirects used in EIGRP?
Cisco routers do not trigger an ICMP redirect based upon which
routing protocol is in use. They have a defined set of
criteria that is based upon the following parameters:
http://www.cisco.com/warp/public/105/43.html
ICMP redirects are in explained in reasonable detail here
(watch wrap):
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ip.htm#
xtocid2236313
The real issue of ICMP redirects is less concerned with
Internet gateways and more concerned with Internet hosts. The
governing RFC here is RFC 1122. It states in para. 3.2.2.2:
3.2.2.2 Redirect: RFC-792
A host SHOULD NOT send an ICMP Redirect message; Redirects are
to be sent only by gateways.
A host receiving a Redirect message MUST update its routing
information accordingly. Every host MUST be prepared to accept
both Host and Network Redirects and to process them as
described in Section 3.3.1.2 below.
A Redirect message SHOULD be silently discarded if the new
gateway address it specifies is not on the same connected (sub-
) net through which the Redirect arrived [INTRO:2, Appendix A],
or if the source of the Redirect is not the current first-hop
gateway for the specified destination (see Section 3.3.1).
Listed above is what the Internet Standard specifies for proper
operation. Let's bounce that against reality as we know it:
http://support.microsoft.com/support/kb/articles/Q243/4/27.ASP
http://support.microsoft.com/support/kb/articles/Q195/6/86.ASP
http://support.microsoft.com/support/kb/articles/Q225/3/44.ASP
As a matter of practice, ICMP redirects have taken the form of
a DoS attack today (at least as implemented in Winthings).
HTH,
Paul Werner
- who envies the serenity of an Oregon sunset.
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