Should routers send redirects by default?

David W. Hankins David_Hankins at
Tue Aug 24 20:25:01 UTC 2010

On Sun, Aug 22, 2010 at 10:12:01AM +0930, Mark Smith wrote:
> o  allow an IPv6 router to indicate to an end-node that the destination
> it is attempting to send to is onlink. This situation occurs when the
> router is more informed than the origin end-node about what prefixes
> are onlink.
> This shouldn't happen very often either, as multiple onlink IPv6 routers
> should be announcing the same Prefix Information Options in their RAs,
> and therefore end-nodes should be fully informed as to all the onlink
> prefixes. ICMPv6 redirects in this scenario would only occur during the
> introduction of that new prefix information i.e. the time gap between
> when the first and second onlink routers are configured with new prefix
> information.

It may be true the situations where redirects are required for this
are few in number, but I think it is not true that the use of
redirects is limited solely to the configuration gap between
introducing a new prefix.

In NBMA networks, it is said that the nodes will have IPv6 addresses
with no covering advertised prefixes ("IPv6 Core Protocols
Implementation", page 393, just spotted while reading today).

Additionally, the typical use of /128 "role addresses" for services
aliased onto lo0 mean the router has a /128 route for the role address
to an on-link device, but a covering prefix advertisement would be
both futile and inappropriate.

I don't necessarily want to say that your conclusion is false, but
rather that it seems to me there are more enumerations in the set.

David W. Hankins	BIND 10 needs more DHCP voices.
Software Engineer		There just aren't enough in our heads.
Internet Systems Consortium, Inc.
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