Please see in line below with "<hs>"
-----Original Message-----
From: Ralph Droms (rdroms)
Sent: Friday, June 29, 2007 10:26 AM
To: JINMEI Tatuya / ????
Cc: IETF Mailing List IPv6; Wes Beebee (wbeebee); Hemant Singh (shemant)
Subject: Re: draft-wbeebee-nd-implementation-pitfalls-00 with urgent
changessuggested to 2462bis-08
On Jun 28, 2007, at Jun 28, 2007,1:14 AM, JINMEI Tatuya / 神明達哉
wrote:
> At Wed, 27 Jun 2007 14:27:37 -0400,
> Ralph Droms <[EMAIL PROTECTED]> wrote:
>
>> One bug that may or may not be common is to make assumptions about
>> the prefixes on a link based on addresses assigned to an interface.
>> I can imagine (and I believe we've actually made a real sighting of
>> this scenario) that an IPv6 implementor might extrapolate IPv4
>> conventions and extract the /64 prefix from an assigned address
>> (either SLAAC, DHCP or manual config), and add a route to the host
>> table indicating that the prefix is on-link, regardless of whether
>> the prefix is advertised as "on-link" in an RA.
>
> [...]
>
> If the system administrator manually configures an IPv6 address with a
> prefix length smaller than 128, the kernel will assume that the
> corresponding prefix is on-link. But I believe this should be
> reasonable.
>
> JINMEI, Tatuya
> Communication Platform Lab.
> Corporate R&D Center, Toshiba Corp.
> [EMAIL PROTECTED]
I see where draft-wbeebee-nd-implementation-pitfalls also mentions manual
configuration as a special case:
2. The RA and ICMPv6 Redirects from the default router are the only
sources of information for on-link determination. DHCPv6 or any
other configuration on the host MUST NOT be used for on-link
determination. Manual configuration of a host introduces its own
set of security considerations and is beyond the scope of this
document.
Is there some reason to believe the information about on-link prefixes should
be implicitly overridden in the case of manual address assignment? I can
understand explicitly overriding information from RAs by manually configuring
the on-link information as a separate step from manual address assignment. But
it seems to me that assuming the prefix from a manually configured address is
on- link might cause unexpected loss of connectivity if the prefix does require
off-link delivery through the router.
<hs> If the host has been manually configured for IPv6 address where the host
was also configured for prefix and prefix length, then what's on-link for this
host can be determined by host. But what if manual configuration configured an
IPv6 address and maybe, also the prefix, but forgot to configure prefix length.
Then this manual configuration has no means to determine what's on-link for a
destination based on the data from manual configuration. I have host not
assuming a default prefix length yet. The RA has been explicitly ignored. So
not this host has no choice but to send non-link-local traffic to the default
router. Specifying manual configuration behavior and its interaction with RA is
a can of worms that will take time to clear up.
Hemant
- Ralph
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