HI JinHyeock,
On 7/5/06, JinHyeock Choi <[EMAIL PROTECTED]> wrote:
Dear Samita
I went over the draft and gladly find many similarities with 'IPv6
over 802.16' work. For example, an Access Router in PAN (PAN
coordinator) has the complete list of all the (link-local) addresses
on the link' and WiMAX AR (ASN GW) is also an omniscient AR. It seems
that we think along the similar line.
Agree.
Kindly find my in-line comments.
Thanks for your comments.
Sec 3.
> 2. When the host initializes its network it multicasts one or a few
> Neighbor Solicitation messages to the all-router IPv6 multicast
Typo. sub/ Neighbor/ Router.
Ok.
Sec 5.1.
> The lowpan nodes MUST include a Sender Link-layer Address option in
> the Router Solicitation, since this then allows the router to unicast
> a Router Advertisement in response.
The above is possible only after DAD is completed, which results in
delay. How about including 'Tentative Option' instead?
Are you talking about Optimized DAD? How much time should we be saving?
Will it be worth the extra code ?
This document is only concerned with the base ND changes.
> Since every host sends a RS when it attaches to the PAN and there is
> a single router for the PAN (the PAN co-ordinator), this router will
> observe the arrival of all the IPv6 link local addresses
This may not be so. Allow me an example. When a host attaches to a
network, while performing DAD, it may receive an unsolicited
(periodic) RA. Then the host would not send an RS. Also the host may
generate a new (link-local) address while staying at the same link for
the privacy reason. Then it would simply configure a new address
without sending an RS.
In case of LowPan-ND, we are requiring to send unicast RS to the IPv6-router.
We have not decided whether DAD should be mandatory for these devices or not.
Since this draft assumes each node has EUI-64 addresses, DAD may not be
required in theory. But in practice, it may choose to do DAD through
the Ipv6-router.
However, it will not receive unsolicited RA while waiting on DAD, because in
this ND-extension RA will happen (most likely) through unicast L2 messages.
Since both the DAD and RA will be sent by the same Ipv6 router, I'd assume
they will happen in sequence. But due to radio link issues, we cannot guarantee
that one will reach the destination always in sequence. Perhaps, we
need to re-word the above mentioned text to clarify "observe the
arrival..." part of the sentence.
How about monitoring the incoming DAD NS to generate the list instead?
That's the approach WiMAX takes right now.
Will discuss that. As mentioned above that DAD may not be mandatory.
Sec 5.2.
> Firstly, it might very well be possible to increase the default time
> significantly as long as the hosts can use some other mechanism to
> detect when the router (the PAN co-ordinator) disappears.
We also try to increase the maximum of MaxRtrAdvInterval.
What was the value? Which draft is it in?
Sec 7.
> Should nodes in LowPan network use duplicate address
> detection Avoiding duplicate address detection will save broadcast
> signaling in the PAN-since 802.15.4 does not have multicast
> capabilities.
I have difficulty understanding the above. Kindly clarify.
Sorry, that sentence is problematic. We are missing a punctuation.
It means that DAD means broadcast in 802.15.4 network and should we
skip DAD for 802.15.4 network?
Sec 11
> It is assumed that the node knows the router's IPv6 address on the
> link.
Usually this is not possible for 802.16/ WiMAX.
How does it know its router address then? Does it know router's
link-layer address to send DAD?
> The node sends a Router Solicitation message directly to the
> router's link-local address.
In WiMAX, the node sends an RS with all-router multicast destination
address. However, WiMAX specific forwarding mechanism ensures that the
RS is delivered to the AR in unicast.
Ok. The above line actually meant the same, but it did not specify the
L3 address
and the destination IP-address should be
multicast address as specified in IPv6, but the link layer sends it to
the L2-unicast
address. So we are in sync.
> This RS message MUST carry sender's
> link-layer address (SLLA) option.
If the RS is sent before completing DAD, it can't carry SLAA. In that
case it may carry Tentative Option.
Can you please point me to the Tentative Option document?
> The
> default periodic interval should be set by the link-layer technology
> specific requirements.
In WiMAX, it may not be efficient to send RA every 30 mins (current
Max MaxRtrAdvInt) I learned that, in cellular environments, mobile
stations remain idle for the majority of time. (Even it's not
unthinkable to spend more than 90% of time in idling mode
contemplating my own cellular phone usage.) So WiMAX developers are
not happy at the prospect of having to page and awaken 90% of dormant
nodes for every 30 mins.
I think Wimax has some other mechanism for sending 'Fast-RA' during
device attachment time and then it sends RS to followup. So it is
perfectly alright
not to have a periodic RA. In that case RA interval is infinity :-)
> This causes the router
> to both forward the packet to the target and send a Redirect message
> back to the sender. The redirect can include the L2 address for the
> target,
In WiMAX, the router would not send a Redirect message. Usually L2
address is not used for data forwarding inside a link. In WiMAX, an MS
has only an AR, a default router, as its on-link neighbor.
Please see section 10 of this draft for application on other technologies.
RFC2461 actually recommends using off-link RA advertisements for
the non-broadcast/non-multicast networks neighbor soliciation. This is
not new in this draft.
> The router
> sends router redirects for the target on-link IP address to the
> sender node A. The router redirect carries the target link-layer
> address option.
As I wrote the above, an MS has only its AR as its on-link neighbor in
its Neighbor Cache. So I don't think it's necessary for AR to relay an
address resolution query.
So, according to your description, each MS is off-link to the other.
So any packet has to be forwarded to the AR first. It sounds like
the AR needs to have a different IPv6 link and L2 link (for each MS),
such that an IPv6-link consists of multiple MSes.
So, if AR follows IPv6 neighbor discovery it should advertise RA with L=0
and all data packets are forwarded through it like a star topology in 6lowpan.
Thanks for pointing out the differences in Wimax technology. As I mentioned
before, this draft only provides guidelines for other technolgies so that
mimimal change is required to adopt IPv6 ND on other non-broadcast/multicast
networks.
Regards,
-Samita
I wish the above helps.
Thanks for your kind consideration.
Best Regards
JinHyeock
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