Hemant Singh (shemant) wrote:
The summary from this section snipped from 6.3.4 of RFC 4861 is saying
no on-ink information does not mean off-link. So why is the text is red
where is says, send traffic to default router being said because the
text in red signals off-link behavior. Why is this paragraph not
ambiguous?
For security reasons I don't do anything fancy in my mail reader, hence
I don't see the colors your refer to.
Anyhow, what it is saying is that the L=0 is a no-op.
Elsewhere in the document it explains how the prefix list is maintained
and used, which basically means that all the prefixes with L=1 are
considered (within their lifetime).
The reason things are done this was is that there might be a reason to
send a prefix option with some bit other than L set, and that can't
interfere with the prefix list.
A concrete example would be a router sending a prefix information option
with only R set (see RFC 3775) and the fact that L=0 in such an option
shouldn't delete anything from the prefix list maintained by the host.
Erik
Prefix Information options that have the "on-link" (L) flag set
indicate a prefix identifying a range of addresses that should be
considered on-link. Note, however, that a Prefix Information option
with the on-link flag set to zero conveys no information concerning
on-link determination and MUST NOT be interpreted to mean that
addresses covered by the prefix are off-link. The only way to cancel
a previous on-link indication is to advertise that prefix with the
L-bit set and the Lifetime set to zero. The default behavior (see
Section 5.2) when sending a packet to an address for which no
information is known about the on-link status of the address is to
forward the packet to a default router; the reception of a Prefix
Information option with the "on-link" (L) flag set to zero does not
change this behavior. The reasons for an address being treated as
on-link is specified in the definition of "on-link" in Section 2.1.
Prefixes with the on-link flag set to zero would normally have the
autonomous flag set and be used by [ADDRCONF].
Hemant
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