Hi Colin, Admittedly I know better 4861 than 6lowpan-nd but I think the "conceptual sending algorithm" is mostly the same. So let me try to answer based on my understanding...
[Colin] I appreciate the link to that description, as it raises some other
questions
for me. In 6lowpan-nd it specifically says that anything but link-local is
off-link, in which case you wouldn't use the NC for anything but link-local
correct?
[Mathilde] Correct, although you still need the NC to find the mapping
between the default router IPv6 address and its L2 address
[Colin] I had assumed the NC could be used to check if a specific address
was
on-link or not in the absence of other information. From RFC4861 definition:
Neighbor Cache
- A set of entries about individual neighbors to
which traffic has been sent recently. Entries are
keyed on the neighbor's on-link unicast IP address
and contain such information as its link-layer
address, a flag indicating whether the neighbor is...
But 6lowpan-nd says anything but fe80:: is off-link. Thus if you have a
message to a global prefix device, you always send to the default router?
[Mathilde] yes; default router or next-hop as specified by the routing
protocol.
[Colin] Thus lacking a routing protocol, how could a 6LR send a NA to a 6LN
if that
6LN registered a global address? The 6lowpan-nd-examples currently have
this:
If Status is a Success:
6LR ---------NA-Reg------->6LN
Src= LL64 (6LR)
Dst= GP16 (6LN)
ARO with Status = 0
If this is 'illegal' then I take full credit for not fully understanding how
IPv6 works in creating that example ;-) But I think other people were
assuming that would work fine as well w/o a routing protocol.
[Mathilde] ] My understanding is that registrations are treated differently
as traditional ND entries (or tentative NCE). Like traditional entries they
contain the IPv6 address / l2 address mapping however in terms of
"conceptual sending algorithm behavior" they are more like routing table
entries.
-----Original Message-----
From: Mathilde Durvy (mdurvy) [mailto:[email protected]]
Sent: October 8, 2010 8:42 AM
To: Colin O'Flynn; [email protected]
Subject: RE: [6lowpan] 6lowpan-nd neighbour table collision
Hi Colin,
It seems to me that if the addresses are global, presumably built on a
off-link prefix there is no problem.
> The ABR is address fe80::33:44 so it will now send a multihop ND message.
> The regular IPv6 sending algorithm will first search the NC for
connectivity
> before sending through the default router (fe80::11:22).
Actually what the IPv6 algorithm says is
" Next-hop determination for a given unicast destination operates as
follows. The sender performs a longest prefix match against the
Prefix List to determine whether the packet's destination is on- or
off-link. If the destination is on-link, the next-hop address is the
same as the packet's destination address. Otherwise, the sender
selects a router from the Default Router List"
" Once the IP address of the next-hop node is known, the sender
examines the Neighbor Cache for link-layer information about that
neighbor."
Best,
Mathilde
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