> -----Original Message----- > From: Wes Beebee (wbeebee) [mailto:wbee...@cisco.com]
> WB> The fact that Redirects cannot signal that an address is > off-link derives from an extremely subtle and non-obvious > consequence of the application of the Redirect message > processing rules in section 8.1. It was so subtle, that we > even missed it the first time until Thomas explained it to > us. A Redirect message is silently discarded if it does not > have an IP source address that is the same as the current > first-hop router for the specified ICMP Destination address. > This is the processing rule. Proof by contradiction: If you > wanted to construct a Redirect to signal that a destination > which the host believes is on-link is actually off-link, then > you would have to select an IP source address that matches > the current first-hop router for the destination (which the > host believes is on-link). However, since the host believes > the destination is on-link, the host will not forward the > packet to any first-hop router (because it's on-link). > Therefore, no valid IP source address > can be chosen for the Redirect (because there is no > first-hop router for the destination, because the host > believes the destination is on-link). Contradiction! > Therefore, the assumption, that you can construct a Redirect > to signal that what a host believes is an on-link destination > is actually off-link, is false. Can't the explanation be simpler? A redirect is sent by a first hop router back to the sending host. However, if the sending host thinks that the destination address of its packet is on-link, it will not send the packet to a router. No router in the path --> no one to generate a redirect. Bert -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
