To give a little more detail to that implementation bug, it seems the
host implementation inferred an on-link prefix from an address
assigned through DHCPv6. We believe the implementation carried over
IPv4 behavior, in which it's common to pass on-link prefix information
to a host as a side effect of address assignment to interfaces. In
IPv6, of course, RAs provide an explicit path for announcing prefix
information, so no prefix state should be inferred from address
assignment.
In my opinion, the "no PIO" case is adequately described in RFC 4861,
as the host has no information about on-link status of a prefix if
there is no PIO for that prefix. Therefore, the host should send any
outbound traffic to an address from a prefix for which the host has
not received a PIO to the default router.
- Ralph
On Dec 5, 2007, at Dec 5, 2007,4:05 PM, Hemant Singh (shemant) wrote:
Erik,
As I said in the presentation, let's forget the aggregation router.
The
host implementation bug we found is reproduced in an Ethernet LAN
network too. An RA from the router was sent where RA was NOT signaling
on-link and the host still behaved as on-link for traffic forwarding.
The RA we used was an RA that did not send any PIO (Prefix Information
Option). BTW, such a case (RA with no PIO) is not even covered by the
definition of on- and off-link in section 2.1 of RFC 4861, especially
since section 2.1 goes to so much copious details to describe on-link.
I was looking for a Turing machine to signal off-link.
Hemant
-----Original Message-----
From: Erik Nordmark [mailto:[EMAIL PROTECTED]
Sent: Wednesday, December 05, 2007 12:29 PM
To: Hemant Singh (shemant)
Cc: Suresh Krishnan; ipv6@ietf.org
Subject: Re: Off-link and on-link
Hemant Singh (shemant) wrote:
Suresh,
At least our drafts do not ask for a new off-link flag. Without a new
off-link flag your scenario will have to go with (a). But do note,
aggregation routers do not send Redirects. So the scenario below
cannot be even supported on aggregation routers.
Which RFC defines an "aggregation router"?
Erik
Hemant
-----Original Message-----
From: Suresh Krishnan [mailto:[EMAIL PROTECTED]
Sent: Wednesday, December 05, 2007 11:01 AM
To: ipv6@ietf.org
Subject: Off-link and on-link
Hi Hesham/Dave/Erik,
I am not taking a stand on whether an explicit off-link flag is
necessary/useful or not, but I have encountered a scenario where the
existing algorithm specified in RFC4861 does not work very well.
Let's
say a router wants to signal to the clients that 2001:dead:beef::/48
is on-link except for 2001:dead:beef:abcd::/64 that is off-link. How
would it go about describing this? I see two ways
a) Advertise the /48 with L=0 and send redirects for all addresses
not
on the /64
b) Advertise the /48 with L=1 and the /64 with Q(the new off-link
flag)=0
I see b) as being more efficient than a)
P.S: I do not think that this scenario is very likely, just possible.
Cheers
Suresh
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