James Carlson wrote:
Alexandru Petrescu writes:
While the document does talk about stateless address autoconf I
think it should also talk about ND. I think it should mention
whether - or not - it's possible, feasible, has been done or
probable, to run IPv6 ND over a ppp link.
It's being done today. RFC 2461 specifies that ND is supposed to be
run on point-to-point links.
Yes, it does. But not clear whether peer sends NS to the other peer or
not; or whether peer sends NA or not. Why would it if there's no
link-layer address.
Not clear what a NC entry looks like when there's no link-layer address.
Not sure what a link-local multicast address looks like over a
point-to-point link: still ff02::1 and ff02::2 (link local)? Or ff01::1
and ff01::2 (interface local - since both interfaces are tightly connected)?
Not sure the solicited-node address (FF02:0:0:0:0:1:FFXX:XXXX) does
still use the last 24 bits of the Interface ID derived by IPv6CP.
Not sure whether an anycast IID can or shouldn't be negotiated by
IPv6CP. If the peer is a router it must use a subnet-router 64-0bits
anycast ID on an interface (rfc4291), but ConfigReq with a 0 InterfaceID
is sign of negotiation initiation, not conclusion.
Not sure about an 'anycast ID' rfc2526, which is on 7bits and is part of
the IID, and is same on both peers. That RFC also says no IID should
ever contain the first 54bits all-ones, so IPv6CP negotation should at
least ensure it never negotiates IIDs whose leftmost 54bits are all ones.
Maybe all of these are out of scope when ND runs over a point to point link?
If yes, then the SLLAO/TLLAO options (source link-layer address
option, and target) could be encoded from the Interface IDs
derived by IPv6CP. And if we talk link-local IPv6 multicast
addresses on the ppp links then also we can have a meaningful way
to describe them.
PPP links don't have layer two addresses; they're point-to-point.
I agree they're point to point.
I don't think I agree that these options ought to be used to convey
the PPP Interface ID values. RFC 2461 says this:
Source link-layer address The link-layer address of the sender, if
known. MUST NOT be included if the Source Address is the unspecified
address. Otherwise it SHOULD be included on link layers that have
addresses.
Note that it says "link layers that have addresses." Point to point
interfaces don't have addresses, and thus ND messages on PPP links
shouldn't include the SLLA/TLLA options.
Sounds logic.
To me STLLAOptions carried in ND messages is a good means to have easy
ND when there's no link-layer header to carry link-layer addresses.
2) The access router terminating the PPP link does not
autoconfigure any IPv6 global unicast addresses from the prefixes
that it advertises.
Not sure I understand the 2nd condition here. Is it that we don't
want the AR to _statelessly autoconfigure_ (a router never does
anyways) or that we don't want the AR to have an address in same
prefix as the host? How would absence of global address on AR help
avoiding DAD?
In that case, there'd just be one address on the link for the given
prefix. If there's only one address, you can't possibly have a
conflict.
So one would have to prohibit the manual ('administrative') assignment
of that address on the interface too, not just the 'autoconfiguration'
assignment of that address. A router doesn't autoconfigure an address
based on the RA it sends, neither based on an RA it receives.
Also, a router must assign a subnet-router anycast address (rfc4291) on
the routing interface, that is a prefix::0/128 address; so at least that
address must be assigned on the interface.
Or maybe I don't understand 'autoconfigure' as you do.
I also think since ppp is used to connect to an Access Router that
that AR should be a default router, i.e. we can state it in terms
of ND RA lifetimes.
?
A PPP link may or may not represent a link to a router with
sufficient connectivity to be a useful "default router." The only
way you know is if that router tells you so.
Ok.
We don't want both of them to be routers and advertise themselves as
default routers either.
Still in the section stateless autoconfig, it would be worth
mentioning whether the initial RA is sent to all-nodes link-local
address, or to the link-local address that the PPP server delivered
to the host.
I believe that you can do either, and that both should (must) work.
For what it's worth, PPP isn't client-server -- it's peer-to-peer.
One end of the link isn't necessarily privileged in any manner,
though in sostme particular usages (deployments) this is so.
Yes, I agree - a subsequent reading of the draft reads that the
negotiation reads indeed peer to peer behaviour.
Alex
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