[DNA] [Issue 15] [Issue 16] DAD and MLD Interaction

[James Kempf <kempf@docomolabs-usa.com>]

I've been meaning to write this up for some time. Below is some text for a
section to add to draft-pentland about the interaction of DNA with host
address configuration, both unicast and multicast. It covers stateful and
stateless address configuration. The text is intended to be for a new
section in draft-pentland, presuming, of course, that the WG approves
draft-pentland as the basis for the WG draft.

Comments?

            jak

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5.2.5 DNA and Address Configuration

When a host moves to a new link, a potential exists for a change in the
validity of its unicast link local and global addresses, and its multicast
addresses. In this section, host processing for address configuration is
specified. The section considers both statelessly and statefully configured
addresses.

5.2.5.1 Duplicate Address Detection

A DNA host MUST support optimistic Duplicate Address Detection [RFCoDAD] for
autoconfiguring unicast link local addresses. If a DNA host uses address
autoconfiguration [RFC2462] for global addresses, the  DNA host MUST support
optimistic Duplicate Address Detection for autoconfiguring global unicast
addresses.

5.2.5.2 DNA and the Address Autoconfiguration State Machine

When a link level event occurs indicating that the host has moved from one
link to another, DNA requires the host to determine whether a change in IP
link has occured by sending an RS. The DNA host SHOULD select one of its
link local addresses that is in the "Confirmed" state (i.e. assigned to an
interface) and utilize that as the source address on the DNA RS. If the host
has no "Confirmed" link local addresses but does have an address in the
"Optimistic" state, it MUST utilize that as the source address. Since
optimistic Duplicate Address Detection is required for DNA, the host should
not have any addresses in the "Tentative" state. If the host currently has
no link local addresses, it MUST construct one and put it into the
"Optimistic" state. Note that the presence of a duplicate link local address
 on the link will not interfere with the ability of the link to route a
unicast RA from the router back to the host, because the TSLLA option is
included in the RS and is utilized by the router on the RA frame.

If the host receives no RA in reply, it MUST transition all addresses to the
"Optimistic" state and act according to [RFC2461] as if no router has been
discovered on the link.

If the received RAs indicate that the host has not moved to a new IP link
(i.e. the IP link has not changed) either because a DNA RA has been received
or nonDNA RAs have been received and the host performs CPL, then the host is
REQUIRED to leave the state of all "Confirmed" and "Optimistic" addresses
unchanged and continue with optimistic Duplicate Address Detection for
"Optimistic" addresses. This includes both unicast link local and
statelessly autoconfigured unicast global addresses (but not statefully
configured global unicast addresses).

If the received RAs indicate that the host has moved to a new IP link (i.e.
the IP link has changed), either because a DNA RA has been received or
nonDNA RAs have been received and the host performs CPL, the host MUST
transition all autoconfigured addresses in the "Confirmed" state to
"Optimistic" and begin optimistic Duplicate Address Detection signaling for
them. Optimistic Duplicate Address Detection signaling for "Optimistic"
addresses MUST also be restarted and continued until either a duplicate is
detected or the signaling timeout occurs, according to [RFCoDAD].

5.2.5.3 DNA and Statefully Configured Addresses

The DHCPv6 specification [RFC3315] requires hosts to send a DHCPv6 CONFIRM
message when a change in link is detected. Since the DNA protocol provides
the same level of movement detection as the DHCPv6 CONFIRM, it is
RECOMMENDED that DNA hosts not utilize the DHCPv6 CONFIRM message when a DNA
RA is received, to avoid excessive signaling.

When a DNA RA is received, statefully configured addresses are handled
similarly to autoconfigured addresses. If the received RA indicates that the
host has not moved to a new IP link, the statefully configured addresses are
still valid and can continue to be used until their lease expires. If the
DNA RA indicates that the host has moved to another link, the host is
REQUIRED to begin stateful configuration again.

If, however, a nonDNA RA is received, the host SHOULD use the DHCPv6 CONFIRM
message as described in RFC 3315 rather than wait for additional RAs to
perform CPL, since it reduces the amount of time required for the host to
confirm whether or not it has moved to a new link. If the CONFIRM message
validates the addresses, then the host can continue to use them. If not, the
host MUST perform DHCPv6 stateful address configuration again, as described
by RFC 3315.

5.2.5.4 Change in IP Link Address Configuration Type

It is possible that a host may encounter a change in IP link address
configuration type (for example, from stateful to stateless) when it moves
from one IP link to another. The solicited RA will indicate what type of
address configuration to perform in this case, and MUST be followed.

In general, a change in IP link address configuration type should not occur
if the host does not change IP link. However, if the initial DNA RA
indicates that the host has not changed IP link but the IP link address
configuration type is different from the last indication of the address
configuration type on the link, the host SHOULD wait for additional RAs
before beginning address reconfiguration. If all RAs agree as to the address
configuration type change, then the host MUST perform address
reconfiguration as specified by the RAs even though it has not changed to a
new link. If the RAs do not agree, then it is likely that the routers are
misconfigured, and the host MAY continue to use previous addresses as
described above, but an error message should be logged to inform the network
administrator, and the host should be vigilant for possible errors.

5.2.5.5 Multicast Address Configuration

If the returned DNA RA indicates that the host has not moved to a new IP
link, no further action is required for multicast addresses to which the
host has subscribed.

If, on the other hand, the DNA RA indicates that the host has moved to a new
IP link, the host MUST issue MLD [RFC3810] messages to the router for
subscribed multicast addresses, including the
Solicited_Node_Multicast_Address for any unicast addresses configured.