One document matched: draft-oneill-mip-multicast-00.txt
Personal A. O'Neill
Internet Draft Flarion Technologies
Document: draft-oneill-mip-multicast-00.txt 5 July 2002
Expires: Dec 2002
Mobility Management and IP Multicast
<draft-oneill-mip-multicast-00.txt>
Status of this Memo
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all provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
Mobile IP provides a mobile node, that visits a foreign subnet, the ability
to continue to use an address from its home subnet (the home address) as a
source address. This is achieved through the allocation of a Care of Address
on the foreign subnet that is used as the end-point of a redirection tunnel
from a home agent on the home subnet. Mobile IP in RFC 3220 states that when
the mobile node originates multicast traffic intended for the foreign
multicast system, it can only do so by first obtaining an IP address from the
foreign subnet (a Collocated Care of Address) and then using this address as
the multicast source address. This is to ensure that the source address will
pass multicast routing reverse path forwarding checks.
This foreign multicast model is however extremely restrictive, and still very
problematic to multicast routing and applications when the mobile node
regularly changes foreign subnets, as is common in wireless systems. This is
because the source address continues to evolve which must be tracked by
source specific multicast application and routing signalling. Using the home
multicast system, again described above, is also non-optimal because the
mobile node receiver is then serviced by packets that must be tunnelled from
its home agent which, removes any multicast routing benefits (ie network
based tree building). This draft therefore describes modifications to the
foreign multicast interface between mobile IP and multicast routing that
enable the mobile node to use its persistent home address as a multicast
source address.
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INDEX
Abstract
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . . . . 3
3. Terminology used in this document . . . . . . . . . . . . . . . . . 3
4. Motivation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Limitations of MIP Multicast. . . . . . . . . . . . . . . . . . . . 4
5.1. Commercial Implications. . . . . . . . . . . . . . . . . . . . 4
5.2. Foreign Multicast System in RFC3220. . . . . . . . . . . . . . 4
5.3. Home Multicast System in RFC3220 . . . . . . . . . . . . . . . 5
5.4. Non-Member Senders . . . . . . . . . . . . . . . . . . . . . . 6
5.5. Reverse Tunnelling Enhancements from RFC 3024. . . . . . . . . 7
5.6. The Problem with CCoAs . . . . . . . . . . . . . . . . . . . . 8
6. HoA based MIP Multicast . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Hybrid Multicast System. . . . . . . . . . . . . . . . . . . . 10
6.2. Shared Tree Solution . . . . . . . . . . . . . . . . . . . . . 12
6.3. MIPv4 FA Multicast Encapsulation, MIPv6 RPF Redirect Option. . 13
6.4. Multicast Signalling Extensions - RPF Redirection. . . . . . . 14
7. AAA Support for MIP Multicast . . . . . . . . . . . . . . . . . . . 19
8. IPv6 Considerations . . . . . . . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . . . . 19
10. Notice Regarding Intellectual Property Rights. . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Mobile IP provides a mobile node, which visits a foreign subnet, with the
ability to continue to use an address from its home subnet (the home address)
as a source address. This is achieved through the allocation of a Care of
Address on the foreign subnet that is used as the end-point of a tunnel from
a Home Agent on the home subnet. Mobile IP in RFC 3220 [MIPv4] and in [MIPv6]
states that when the mobile node originates multicast traffic intended for
the foreign multicast system, it can only do so by first obtaining an IP
address from the foreign subnet (a Collocated Care of Address) and then using
this address as the multicast source address. This is to ensure that the
source address will pass multicast routing reverse path forwarding checks as
mentioned, for example, in the MIPv4 RFC text which is repeated overleaf.
From RFC 3220 section 4.4. Multicast Datagram Routing, page 66
A mobile node that wishes to send datagrams to a multicast group also
has two options: (1) send directly on the visited network; or (2)
send via a tunnel to its home agent. Because multicast routing in
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general depends upon the IP source address, a mobile node which sends
multicast datagrams directly on the visited network MUST use a co-
located care-of address as the IP source address. Similarly, a
mobile node which tunnels a multicast datagram to its home agent MUST
use its home address as the IP source address of both the (inner)
multicast datagram and the (outer) encapsulating datagram. This
second option assumes that the home agent is a multicast router.
This foreign multicast model is however extremely restrictive, and still very
problematic to multicast routing and applications when the mobile node
regularly changes foreign subnets, as is common in wireless systems. This is
because the source address continues to evolve which must be tracked by
source specific multicast application and routing signalling. Using the home
multicast system, again described above, is also non-optimal because the
mobile node receiver is then serviced by packets that must be tunnelled from
its home agent which, removes any multicast routing benefits (ie network
based tree building). This draft therefore describes modifications to the
foreign multicast interface between mobile IP and multicast routing that
enable the mobile node to use its persistent home address as a multicast
source address. It concentrates primarily on MIPv4, but mentions related
MIPv6 issues and opportunities, which are brought together in section 8 along
with a detailed description of the present MIPv6 foreign multicast scheme.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to
be interpreted as described in RFC-2119 [RFC2119].
3. Terminology used in this document
Much of the terminology used in this document borrows from Mobile IPv4
[MIPv4], MIP Reverse Tunnelling [RevTun] and IP multicast RFCs and drafts.
This draft introduces the following additional terminology.
Home multicast Multicast via the home IGMP/MLD signalling.
Foreign multicast Multicast via the IGMP/MLD signalling on the visited
Subnet.
Hybrid Multicast Foreign multicast reception, home multicast origination.
Designated Router The DR is the multicast router/forwarder for a subnet.
OldDR / NewDR Sender DRs as part of hand-off between subnets.
RPF Redirection Redirecting the RPF check to point to the FA/DR and not
the multicast source address.
Cross-over Router The furthest router from the senders oldDR on a source
tree that has the sender newDR on a different RPF
interface.
Hand-Off Router The router that issues an explicit Join towards the newDR
and is the closest router from the old DR that has the
newDR on the same RPF interface.
RPF Header An IPv6 routing header indicating the preferred multicast
RPF point for (S,G) packets.
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4. Motivation
The motivation for this work is to enable a mobile node to have the option of
using the more efficient foreign multicast delivery system. This requires the
typical mobile node in wireless systems to use its home address as a foreign
multicast source address, rather than a Collocated Care of Address, and yet
still pass multicast routing RPF checks. This is to enable source specific
multicast application and routing state to survive mobile node hand-offs
between access routers that would typically not survive when using a
Collocated Care of Address. Changes in these multicast source Collocated
addresses would otherwise require multicast receiver application and routing
signalling to be kept informed of each new source address change and to
modify application and routing state in sympathy with such changes. These
changes would unavoidably lead to lost packets and/or excessive signalling.
An associated motivation for this work is to avoid a mobile node, that wishes
to source multicast traffic, from having to acquire a Collocated Care of
Address from each foreign subnet, which is particularly expensive in MIPv4.
5. Limitations of MIP Multicast
5.1. Commercial Considerations
It is clear that MIP typically has a closely coupled policy layer that
enables the home and foreign operators to control MN capabilities and packet
routing when on the foreign subnet. In many cases the home operator wishes
all packets to be routed to and from the home network for security, cost or
customer control reasons. Similarly, the foreign operator also wishes to
protect its own services and users from being affected by the presence of the
roaming MN. In contrast, the foreign operator could alternatively require
that the MN makes use of its own services whilst in the foreign domain and
supporting this is probably a desire by the home operator to divert commodity
traffic flows away from its home network and instead be delivered more
efficiently by the foreign operator. These network and service control
tensions are addressed by the policy layer. They need to be resolved by the
AAA exchanges that occur during the request to connect to the foreign subnet.
This draft does not overly consider which of these commercial models is more
important for MIP multicast and simply aims to make all practical options
available to the parties involved. A discussion of the type of AAA support
required for the specific suggestions in this draft are however outlined in
section 7.
5.2. Foreign Multicast System in RFC3220
The foreign subnet has an IGMP Querier, a multicast designated router (DR)
and at least one Foreign Agent (FA). The IGMP Querier issues Queries to the
all-multicast-systems IP broadcast address, and the multicast DR and other
receive GMRs from the MNs addressed to the multicast group address of
interest. These IGMP messages are transmitted unencapsulated over the foreign
subnet. The foreign multicast system uses native multicast routing from
multicast senders in the Internet, down the multicast distribution tree
towards those DRs that have joined to the group on behalf of their attached
MNs. The DRs then transmit the multicast packets unencapsulated over the
access link to the MN members that are members of the multicast group
identified by the group destination address.
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It can be seen that when multiple DRs in an access network are members of the
same multicast group, and each DR has multiple MNs on that group, that the
use of native multicast forwarding results in a single copy of each packet
from the core of the network out across the access network and over the
access link to the MN members. This represents the potential for significant
bandwidth savings when compared to the home multicast system.
CN HA FA MN
MN with FA CoA
MN Reception CN------------------------------G>----------------->G
MN Origination G<------ NOT PERMITTED
MN with CCoA
MN Reception CN------------------------------G>----------------->G
MN Origination G<----------------CCoA
Figure 1. Forward and reverse foreign network multicast in RFC 3220
MN origination is not permitted when the MN has a FA CoA and hence such MNs
can only receive multicast content. This prevents MIPv4 MNs, which typically
cannot afford to be given a unique CCoA at each FA, nor afford the delay of
continually updating this CCoA on hand-off, from taking part in bi-
directional multicast flows that are typical with RTP sessions, and common in
other multicast data applications.
MN origination is permitted when the MN has a CCoA, with that CCoA used as
the source address. Once again multicast packets are sent unencapsulated over
the access link, this time from the MN to the multicast DR on the subnet.
This router forwards the packets into the multicast tree for the group
contained in the destination address field of the packet. It can be seen here
that whilst the multicast forwarding is bandwidth efficient, through the use
of native multicast, it is limited to MNs with CCoAs.
5.3. Home Multicast System in RFC3220
The home multicast system in RFC 3220 uses a bi-directional tunnel between
the HA and the MN CoA. The MN can have either a FA CoA or a CCoA from the FA
and the resulting forwarding and encapsulations are shown graphically in
figure 1. The MN should set the 'B' bit in the MIP RREQ to request the HA to
forward to the MN, amongst other broadcast traffic, IGMP Queries and possibly
IGMP Group Membership Reports to the MN. The MN can then issue solicited or
unsolicited GMRs for the groups and group senders of interest to that MN, and
the HA can then keep MN specific IGMP state to enable it to make appropriate
forwarding decisions for multicast traffic arriving to the home subnet. Note
that the HA must also export the MN GMRs to the home subnet, so that it can
be seen by the IGMP Querier, received by the multicast DR on the home subnet
for injection into the multicast tree building protocol, and also be seen by
other MNs on the subnet to suppress their own GMRs. The IGMP Queries and GMRs
must be sent encapsulated over the foreign subnet to avoid them being
confused with foreign subnet IGMP signalling, with the encapsulation being
the same as that used for multicast content.
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CN HA FA MN
MN with FA CoA
MN Reception CN----------G>------------------------------------->G
HA===================================>HoA
HA==============>CoA
MN Origination G<---------G<-------------------------------------HoA
HA<===================================HoA
MN with CCoA
MN Reception CN----------G>------------------------------------->G
HA==================================>CCoA
MN Origination G<---------G<-------------------------------------HoA
HA<==================================CCoA
Figure 2. Forward and reverse home network multicast in RFC 3220
The major limitation here is that MN reception of multicast content is via a
unicast tunnel from its HA. This tunnel is required to hide the multicast
content from the foreign multicast system and to identify the target MN (the
HoA/CCoA is otherwise missing due to the multicast packet having a group
destination address). There is then potential for significant replication
load being placed on the HA (and associated loss of bandwidth efficiency)
when significant numbers of registered MNs at that HA are members of the same
multicast group. In addition, when multiple MNs on the same foreign subnet
are members of the same multicast group then multiple copies of the same
content must be delivered to that foreign subnet and delivered over the air-
interface in wireless systems. Only in the case that neither the HA nor the
FA has multiple members of the same group (low membership coherence) is their
no gain to be had from using multicast (network tree building and
replication) between the HA and the FA. In all other cases, the absence of a
multicast delivery tree potentially results in significant inefficiencies.
When comparing the delivery costs (encapsulation processing and overhead) of
multicast and unicast content from the HA in this model, it is evident that
it is potentially better to use a multicast to unicast gateway on the home
subnet and delivery any content using unicast, instead of incurring the
additional cost and complexity of the unicast encapsulation and associated
multicast signalling.
MN origination of content is via a unicast tunnel from the MN to the HA,
using the HoA as a multicast source address. The unicast tunnel is less of an
issue here because source specific branches from senders are common in
multicast tree building and therefore the unicast tunnel does not result in
significant multicast inefficiencies. The tunnel is required simply to hide
the multicast content from the foreign multicast system.
5.4. Non-Member Multicast Senders
It is permitted in the multicast architecture for a host to send traffic
towards a multicast group of which it is not a member. When a host sends an
IGMP GMR for group G, it is specifically asking to be a receiver of the group
but may also wish to send to that group. A non-member sender is not a
receiver on the group and is likely only a transient sender. This is
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typically used to support early media flows in parallel with IGMP processing,
for transient senders that do not wish to disturb the multicast routing
fabric, and for supporting sensor devices that are clearly not interested in
the traffic from other senders. A non-member sender simply originates packets
to the group G and the multicast designated router forwards these into the
multicast receiver tree, without initiating any receiver tree building
activity in the multicast routing protocol. Non-member sender traffic is
still however exposed to RPF checks. Non-member senders can be supported in
either home or foreign multicast systems and therefore IGMP (or MLD)
signalling may not occur before MN originated traffic flows.
5.5. Reverse Tunnelling Enhancements from RFC 3024
Reverse Tunnelling was developed to provide topologically correct tunnels
back to the HA. When the MN has a FA CoA and wishes to tunnel traffic,
including MN originated multicast, back to the HA then in RFC3220 as shown in
figure 2, this is achieved by a MN to HA tunnel using the HoA as a source
address. Unfortunately, the HoA is not a topologically correct source address
and hence risks being dropped in the Internet in routers deploying source
address checking. RFC 3024 instead adds the ability for the tunnel to instead
be initiated from the FA towards the HA and hence being topologically
correct. Reverse tunnelling is requested by setting the 'T' bit in the MIP
RREQ from the MN to the FA and onto the HA. There are then two modes for
forwarding between and the MN to FA. In the default Direct Delivery Style
(DDS), the MN sends the packets unencapsulated to the FA which then tunnels
all received packets to the HA in the reverse tunnel. Essentially, all MN
originated packets are viewed as being home network packets and foreign
multicast is not permitted. Unfortunately, this method does not work however
for multicast packets on a broadcast foreign subnet (not point to point)
because these home broadcast packets will be confused with foreign broadcast
packets by other MNs on the subnet and can be incorrectly received. RFC 3024
therefore mandates the second form of reverse tunnel forwarding known as
Encapsulating Delivery Style (EDS). In EDS, the MN can selectively reverse
tunnel packets to the HA through the use of an encapsulation between the MN
and the FA. EDS mode is selected by the MN in the MIP RREQ by including an
EDS extension as well as setting the 'T' bit.
The EDS extension is not forwarded to the HA and is viewed as purely a local
matter between the MN and the FA. Packets which are encapsulated in a tunnel
from the MN HoA to the FA are switched into a MIP tunnel from the FA CoA to
the HA address. The HA then decapsulates them, and then forwards them onto
the home subnet. The encapsulation on the foreign subnet also means that home
multicast packets are hidden from the foreign broadcast subnet and are
therefore not confusing to other MNs on the foreign subnet. Packets that are
not to be reverse tunnelled are sent natively by the MN to the FA, which then
forwards them normally, which in the case of foreign multicast is down the
multicast tree. Essentially, EDS mode enables a MN to potentially partake in
both home and foreign network multicast at the same time with the
encapsulations over the foreign subnet being used to separate out IGMP and
multicast content from/to the home and foreign multicast systems. Clearly, a
MN would not wish to join the same multicast groups via both systems and so
the MN, FA and HA need to have some configuration or AAA policy to decide
which multicast systems the MN can participate in, and its limitations on
that system (receiver, sender, receiver and sender, multicast group scope).
Additionally, as has been described in 5.1, it is only a CCoA that enables a
MN to originate traffic towards the foreign multicast system.
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5.6 The Problem with CCoAs
Referring back to section 4.4 in RFC3220, the claim is made that MN
origination into the foreign multicast system must use a CCoA. This is
because the multicast source address must be topologically correct to pass
the multicast reverse path forwarding check. This process, which is common to
almost all multicast forwarding engines, is used to build source trees and to
prevent routing loops. This is achieved by having the multicast forwarding
engine in each multicast router, look-up the unicast source address within
each multicast packet, as a unicast destination address in the unicast
forwarding table. If the multicast packet arrives on an incoming interface,
which is also the outgoing interface that would be used to forward unicast
packets to that unicast destination address, then the RPF check has succeeded
and the multicast packet may for replicated and forwarded. Putting aside
transient routing effects, this RPF check will generally succeed for MN
originated packets when the topologically correct CCoA is used as a source
address. However, the RPF check will not generally succeed if the MN HoA is
used as the source address because the HoA is topologically incorrect
(belonging to the home subnet) and hence the multicast packets will not be
received over the interface used to forward unicast packets towards the HoA.
RFC 3220 is therefore correct in its statements and decisions in this regard.
However, RFC 3220 fails to mention that there is an additional problem with
CCoAs. This is that the CCoA is a transient address and must change on each
hand-off if the MN keeps moving. Each such address changes has a damaging
affect on multicast applications and routing. For example, IGMPv3 enables a
host to undertake source specific membership of a group, specifically
enabling a MN to ignore content or receive content only from specific senders
to that group. Protocol Independent Multicast-Sparse Mode (PIM-SM) also has
source specific JOIN and PRUNE mechanisms that act in sympathy with sender
specific group membership signalling to ensure only requested content is
delivered down the multicast tree. In addition, PIM-SM supports both shared
and source specific trees with the source specific PIM JOINs creating (S, G)
state to over-rule the (*,G) shared tree state.
Source Specific Multicast (SSM) is also under development in the IETF in
which the multicast destination group address as well as the senders unicast
address identifies the multicast 'channel', and multicast routers keep (S+G)
state. Finally, multicast transport and session layers applications typically
use the multicast source address to 'demultiplex' content into sender
specific feeds. This is because at a simplistic level, many to many network
multicast is simply a superposition of multiple one to many transport flows.
In all these cases, a change in the multicast source address will create
significant problems, requiring the address change to be communicated down
the tree in advance of the CCoA update, so that new source specific routing
state can be installed for (S2,G) or (S2+G) instead of (S1,G) or (S1+G). It
must also be known to the host so that receiver applications can update
transport, session and application state, to avoid application confusion and
data corruption or loss. The scale of the update (all router and host sender
specific state for that sender) coupled with the likely speed of hand-offs
(and hence CCoA changes), makes the choice of the CCoA as a source address
extremely problematic. Essentially, it completely prevents the MN from using
the foreign multicast system and it must instead use the less efficient home
multicast system. In solving the RPF problem, and preserving the packets of a
single MN originator, it is clear that RFC 3220 creates an even bigger
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problem, with wider implications on multicast routing stability. This is
because the mobility is being directly exposed to the global multicast
routing system through the address change, but is not being exposed to the
unicast system (MIP instead deals with the latter). Note that the use of the
HoA in the home multicast system coupled with the unicast tunnelling back to
home subnet is one obvious way for multicast and MIP to collaborate in
getting the job done. This however misses the efficiency of the foreign
multicast delivery tree. The only way to correct this problem is to use the
MN HoA as a multicast source address for the foreign multicast system
(aligning somewhat home and foreign multicast processing on the hosts) and
then find scalable means for MIP and the foreign multicast routing to work
together to preserve the senders packets through the RPF check process. A
range of techniques are next described in section 6, with the different
techniques potentially forming an evolution and interoperability capability,
as MIP and multicast technologies and standards evolve. They are described in
overview to stimulate discussion between mobility and multicast researchers,
so that standards activity can be commenced to address this opportunity.
6. HoA based MIP Multicast
The aim, in summary, is to enable a MN to originate IP multicast traffic
using the HoA as a source address and have those packets correctly delivered
by the foreign multicast system by specifically bypassing or satisfying the
multicast RPF checks. This needs to work when the MN has requested EDS
reverse tunnelling ('T' bit set plus EDS extension) or when no reverse
tunnelling has been requested ('T' bit unset'). With DDS reverse tunnelling,
it is clear that foreign multicast is by definition prevented and is not
discussed further. An additional requirement is that the MN should not need
to be aware of how the local FA is addressing this problem so that the MN can
simply be made aware that foreign multicast origination is possible and then
undertake home and foreign multicast as befits its configuration, incoming
signalling, and the policy exchanged between the HA and FA. This idealised
foreign multicast system is shown in figure 3 where the MN believes the FA
(specifically the multicast designated router on the foreign subnet if
different from the FA) is able to inject the multicast packets into the
foreign multicast system and the multicast system will safely deliver them
through the Internet to the multitude of CN multicast receivers on that
group. This distribution should at all times be limited by the appropriate
scope of the multicast group. Note that in the idealised system, the MN
processing is the same for both a FA CoA and a CCoA.
CN HA FA MN
MN with FA CoA
MN Reception CN-------------------------------G>---------------->G
MN Origination G<------------------------------G<----------------HoA
MN with CCoA
MN Reception CN-------------------------------G>---------------->G
MN Origination G<------------------------------G<----------------HoA
Figure 3. Idealised Foreign Multicast System
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Before discussing the alternative solutions to this problem, it is important
to point out that these solutions are covered at a relatively high-level and
significant work in standards and subsequent engineering may be required to
turn these suggestions into commercial reality. For now, they should simply
be considered as examples to justify the potentially reality of MIP foreign
multicast, using the HoA as a source address.
6.1 Hybrid Multicast System
The first (early) solution to this problem is to combine the best of the home
and foreign multicast systems in satisfying the problem, thereby creating a
hybrid multicast system. For simplicity, we will assume that the FA is also
the multicast designated router for the foreign subnet. We can also assume
that unencapsulated IGMP and multicast packets with a HoA source address are
intended for the foreign multicast system, whether or not the 'B' bit is set
or EDS RevTun has been requested and the 'T' bit is set. Essentially, we care
greatly about being able to receive multicast via the foreign multicast
system to accrue the bandwidth efficiencies, but care less about the path of
the sender specific MN originated traffic.
The MN may or may not be a member of the multicast group G, whose scope must
encompass both the home and foreign subnets (global scope only). If the MN is
a member of group G then it will have sent an IGMP GMR for group G to the
FA/DR and the FA/DR will have tracked IGMP state and initiated multicast tree
building to add the FA/DR onto the receiver trees for the groups of interest
to its MNs. This MN, and other MNs on that foreign subnet, will then receive
multicast from the FA/DR in an unencapsulated form, and via a bandwidth
efficient foreign multicast tree. We will now discuss how this is
complemented with MN originated traffic.
6.1.1. MNs with FA CoA
The MN originates traffic to the group G by sending unencapsulated packets
onto the foreign subnet with its HoA as a source address and a destination
address of G. On a broadcast subnet, other members of group G on that subnet
will also receive the packet. The FA also receives these packets but instead
of injecting them into the foreign multicast system, it instead reverse
tunnels them to the HA that matches the senders HoA in the visitors list,
with the non-local HoA address acting as the trigger for this redirection.
The HA knows the FA CoA from the registration and should therefore be happy
to receive encapsulated packets from the registered FA CoA to the HA.
Specifically, it needs to be happy to receive multicast packets via the FA
CoA when the 'T' bit is not set. It will of course already be happy if the
'T' bit is set from RFC3024.
The HA has no IGMP state for such packets and treats them as non-member
sender packets by injecting them into the home multicast system without
initiating any receiver tree building. These MN originated packets are
topologically correct at the HA and hence will satisfy any subsequent RPF
checks except under transient routing situations. Note that the FA must first
undertake its own multicast RPF check on the multicast packet using MIP
visitor list state instead of the unicast routing state, before forwarding
the packet to the HA. In addition, the FA needs to deliver the MN originated
packets to other receivers of that group on that FA if the MNs are using
point to point links.
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This is because the multicast routing in the FA must itself not forward the
packets again onto the foreign subnet when received down the multicast
distribution tree, if they contain source addresses matching HoAs in the
visitor list. This is necessary to avoid duplicate delivery on broadcast
foreign subnets and is commonly achieved by the DR installing a source
specific routing entry to discard packets arriving via a unidirectional
shared tree that were originated from that DR.
6.1.2. MNs with CCoAs
When a MN has a CCoA it may or not have registered via the DR, which has an
FA in MIPv4 or an attendant in MIPv6. If the MN has not registered via the DR
then the DR cannot support hybrid multicast by forwarding the MN originated
multicast packets to the HA because it has no state to do so. More
specifically, the DR in this case cannot support MN originated foreign
multicast traffic at all because any packets with a HoA source address,
including IGMP GMRs, are topologically incorrect and hence will be discarded
during ingress filtering in the absence of MIP visitor list state.
If the MN has registered via the DR then the DR will know the MN/CCoA/HA
binding but in addition needs to know the MN/HoA binding to enable it to pass
MN originated packets during ingress filtering and to then be able to tunnel
them to the HA from the DR address. There are clearly ways that the MN could
provide this information to the DR and the HA via a MIP extension, so that
the tunnelling is both possible and acceptable, but this clearly requires the
MN to be aware of the need to add such an extension. Thankfully, this
extension is also required to enable the FA to natively forward unicast
packets from the HoA and hence does not imply that the MN needs to know about
the foreign multicast mechanism. The FA/DR receives the unencapsulated MN
originated multicast packets and forwards them to the HA using the FA/DR
address as a source address. The HA then receives packets from an address
that is not equal to the registered CoA, but is equal to the source address
of the received registration via that FA/DR and hence should be accepted
because the HA and FA share an SA. The use of the HoA as a source address for
foreign multicast can therefore only be permitted if the MN has registered
via the FA/attendent and has informed that node of the MN HoA for ingress
filtering purposes.
CN HA FA/DR MN
MN with FA CoA
MN Reception CN-------------------------------G>---------------->G
MN Origination G<------------------------------G<----------------HoA
HA<=============FACoA
MN with CCoA via FA
MN Reception CN-------------------------------G>---------------->G
MN Origination G<------------------------------G<----------------HoA
HA<=============FACoA
Figure 3. Hybrid Multicast System
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Note that the use of the HoA as a multicast source address implies very
different processing on the MN than the existing use of the CCoA. This is
clearly a significant concern because MIPv6 relies solely on a MN CCoA, and
its use for foreign multicast is potentially broken as discussed in section
8. This effectively means that MNs should be prevented from initiating
foreign multicast content from the CCoA except in the specific case that the
MN is sure that the CCoA will not be changing during the lifetime of the
multicast session. This clearly excludes cellular mobility environments.
6.2 Shared Tree Solution
Some multicast routing protocols, such as PIM-SM, use a shared tree from a
root node out to all receivers. The RPF check in this shared receiver tree is
not made towards the senders unicast address in the multicast packet, but is
instead made towards the root node whose address is distributed to all the
multicast routers. Therefore the RPF problem with a non-local HoA address
only needs to be solved between the senders designated router and the root
node for such shared trees. This can be achieved by using a unicast tunnel
from the DR to the root node, and then have the root node forward the senders
packets down the receiver tree.
CN RP HA FA/DR MN
MN with FA CoA
MN Reception CN----------G>-------------------G>---------------->G
MN Origination G<---------G<-------------------G<----------------HoA
RP<======REG=====FACoA
MN with CCoA via FA
MN Reception CN----------G>-------------------G>---------------->G
MN Origination G<---------G<-------------------G<----------------HoA
RP<======REG=====FACoA
Figure 4. PIM-SM RP MIP Solution
In the specific case of PIM-SM, shown in figure 4, the root node is called
the Rendevouz Point (RP) and PIM-SM already has mechanisms to enable the DR
to tunnel packets directly to the RP using a Register message encapsulation.
In the case of member senders, the RP is able to then try to PIM JOIN back to
the sender via the senders DR and transmit periodic Register Stop messages to
the senders DR. The PIM JOIN is intended to enable the senders DR to send
packets natively to the RP via a source specific branch whilst the Register
Stop is intended to prevent the parallel encapsulation of multicast packets
from the senders DR to the RP in Register messages. In addition to the source
specific branch to the RP from the senders DR, any receiver DR is also
allowed to try to build a source specific branch towards the senders DR and
in so doing bypass the RP and the shared tree.
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In the case of foreign multicast, both of these source specific branches will
be directed towards the HoA in the source address of the multicast packet
(and hence the HA subnet), and not towards the senders DR, which is the FA.
These source specific PIM JOINs will therefore install state that will not be
exercised by packets unless they cross part of the shared tree. The existence
of this state is not a problem however as it will not cause problems and will
eventually safely time out due to the soft state refresh model in PIM. The
Register message could be extended to inform the RP not to bother attempting
a PIM JOIN for this (S,G) and hence avoid wasted PIM JOIN and Register Stop
signalling. In addition, the DR or RP could also periodically send a new PIM
message down the multicast tree to the receiver DRs to also instruct them not
to undertake source specific JOINs for this (S,G).
Comparing this model to the hybrid approach of 6.1, we can see a number of
advantages that accrue when the multicast protocol uses a shared tree and
supports unicast encapsulation to the root node. Firstly, in the hybrid
approach it is clear that senders packets first go to the HA and then
potentially onto the root node within a shared tree protocol. Therefore,
sending the packets directly to the root node removes an additional
encapsulated hop which is specifically useful when the HA and RP and far
apart. In addition, we can see that by leaving all forwarding to the FA/DR we
remove any uncertainties about the scope of group G, that otherwise limits
the hybrid approach to global scope only. Finally, the most widely deployed
multicast protocol in the Internet is PIM-SM and therefore the availability
of a shared tree protocol with encapsulation to the root is generally
assured. This solution does not however address the problem associated with
CCoAs, nor does it deal with other types of multicast routing protocols with
MOSPF a particular concern. MOSPF domains can of course still rely on the
Hybrid solution of 6.2.
6.3 MIPv4 FA Multicast Encapsulation and MIPv6 RPF Redirect Option
The first two solutions rely on a unicast encapsulation to a point at which
the HoA source address can pass subsequent RPF checks. An alternative
solution is to encapsulate throughout the tree using an MIP multicast
encapsulation. The FA encapsulates packets with a non-local HoA source
address that have passed MIP aware ingress checking, using its own address as
the source address and the inner destination group G as the outer destination
address. This packet will then have a topologically correct source address
and can be correctly forwarded by any multicast protocol that builds on-
demand source trees to the receivers of G via (anyFA,G) state. The receivers
will then decapsulate such packets to reveal the original multicast packet
with the HoA source address, which will then be checked against the source
specific host membership state before being passed up to the transport layer.
Essentially the host is prepared to receive from any FA and therefore does
not need to be kept informed of FA CoA changes. Any source specific tree
building triggered by the receiver DR state should be suppressed when the
data is received encapsulated like this. This approach again bypasses the HA
with all the associated benefits, and this time is applicable to multicast
protocols other than PIM-SM which would continue to use the Register
encapsualtion. This however comes at the cost of host (and potentially DR)
complexity, and the bandwidth inefficiency of the multicast encapsulation. In
addition, this clearly does not work directly for explicit join protocols,
the and in general limits any (S,G) pruning to the granularity of the FA
address, such that multiple senders at the same FA cannot be selected/pruned.
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The cost of the encapsulation can be reduced in MIPv6 through the use of a
new hop by hop option header. This 'RPF Redirect' option would be added by
the MN and checked by all multicast routers, and includes the CCoA. The
RPF redirect header therefore provides the opposite binding information to
routers to that provided to the host by the Home Address Option (HAO) The RPF
Redirect option would then be used in multicast routers to redirect RPF
checks towards the senders DR instead of the HoA. The RPF Redirect Option or
the source address of the FA encapsulation technique can be used by hosts to
redirect source specific joins and prunes towards the newDR address, rather
than towards the multicast source address of the original multicast packet.
These redirections are clearly however affected by FA changes and this issue
will be left for discussion in section 6.4.4.
6.4 Multicast Signalling Extensions - RPF Redirection
Section 6.3 handles the RPF problem in the data plane, but an alternative is
to handle it in the multicast signalling plane. This is a longer-term
solution in that changes to multicast signalling need to be widely deployed
throughout a domain before they can be used, and because of the time to
design, standardise and implement changes to deployed protocols. Essentially,
the multicast RPF mechanism and the signalling in each routing protocol needs
to be extended to support an arbitrary RPF point for the (S,G) in question.
This is known henceforth in this document as RPF redirection and is analogous
to the aims of the RPF Redirect option previously mentioned.
During hand-off, the CoA address is changing at the senders end and therefore
each sender DR needs to advertise the new RPF point for that sender. This is
achieved by injecting an RPF Redirect message into the multicast routing
system using hop by hop multicast protocol signalling that is sent down the
present tree or broadcast to multicast neighbours (protocol specific). In the
latter case, each router passes the current RPF point to any subsequent
joiners so that the sender DR only needs to undertake a periodic refresh of
the RPF point in the absence of mobility. In the former case, the RPF point
needs to be flooded rapidly by routers that detect that the old and new RPF
points are on different interfaces so that the rapid flood is limited to
those routers that are affected by the change. Note that the change in the
senders DR might take the MN to a newDR that has no other members of group G,
and also leave the oldDR with no other members of group G. Therefore some of
the above RPF redirection signalling can be coupled with tree building
activity (join/prune/membership flood) at the old and newDRs.
When the MN originator undertakes a hand-off, the oldDR and the newDR need to
collaborate to update the RPF point. There is a cross-over router in the
vicinity of both the old and new DRs that is the last router that would
discard packets from the MN sent via the new DR, when using the oldDR as an
RPF point. The newDR and all intermediate routers to the cross-over router
need to be on the sender multicast tree for the group of interest, and must
have the RPF point set to the newDR, in advance of multicast data being sent,
to avoid that data being discarded. Once on the tree, then the newDR needs to
send periodic RPF Redirects from the newDR to maintain the RPF point and the
tree. At the same time, the receiver tree must also be updated. The precise
mechanisms are of course multicast protocol specific due to the wide range of
protocol mechanisms such as explicit join (PIM), member report broadcast
(MOSPF), and data flood and prune (DVMRP) as examples.
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6.4.1 PIM-SM Example (SSM also)
PIM uses explicit join/prune messaging to build either a shared tree from the
RP, or source specific tree using the source address contained in multicast
packets received on the shared tree. A source tree or Register encapsulation
can be used between the DR and the RP in the case of a shared tree. During a
hand-off on a shared tree with a source specific branch to the RP, the oldDR
first needs to send an RPF Redirect down the multicast tree to first seek out
the cross-over router. The RPF Redirect message contains the old DR address,
the destination group address, the HoA source address, and the newDR address.
The cross-over router is identified by the next hop router towards the RP,
termed the Hand-Off (HO) router, which detects that the RPF Redirect message
does not affect the local RPF check because the oldDR and newDR interfaces
are already the same. This router therefore issues an immediate JOIN towards
the newDR to create (S,G,<newDR) state where the third <field indicates the
RPF point and is a specific extension to the PIM Join message. This combines
with the existing (S,G,<oldDR) state in the cross-over router to preserve
packets from either DR during the hand-off, and is then passed up through the
intermediate routers to the newDR. The newDR can then forward packets down
the (S,G,<newDR) tree. Whilst waiting for this join, the multicast packets
can be sent via the oldDR (ie via the old link or via the new link and a
reverse tunnel to the oldDR) down the (S,G,<oldDR) tree, or can alternatively
use a Register encapsulation to the RP. The HO router also passes the RPF
Redirect down the tree to redirect oldDR state towards the newDR, setting a
flag bit to indicate that the HO router has already been passed to suppress
any immediate Join signalling in subsequent nodes. Note that this subsequent
signalling between the HO and the RP can proceed relatively slowly compared
to the signalling between the oldDR and the HO and between the HO and the
newDR. This HO signal can also trigger the RP to commence issuing Register
Stop messages to the newDR in the absence of the reception of Register
encapsulated multicast data from the newDR. The cross-over router can issue a
prune back towards the oldDR when it receives the join from the HO but should
probably only do so once packets are received from the newDR branch over the
new incoming interface. In the absence of such a prune normal PIM soft-state
timers will still succeed in removing the oldDR branch in a less timely
manner.
It is clear that, between the RP and the receiver DRs on the shared tree, the
routers keep (*,G,<RP) state and hence the RPF Redirect message can be
suppressed at this point. The Redirect message should be propagated however
if the operator wishes to suppress or redirect receiver DRs joining to a
source tree. The redirect message informs the receiver DRs that the source
specific join state should be (S,G,<newDR) and not (S,G,<S) and configuration
in the receiver DRs or a flag in the Redirect message from the RP can control
whether or not the source tree is permitted. Once again the source specific
Join message needs to include the newDR as the RPF point, as well as the
source address, and the message must be routed towards the newDR and not the
source address.
If the source tree is permitted, then the source join will be directed
towards a last DR that may not be the newDR due to a subsequent hand-off. The
last DR should therefore send an immediate Redirect pointing to the newDR,
which requires the last DR to keep hand-off state for a small number of
seconds. This should ensure that the source join can rapidly catch-up with
the movement of the MN.
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6.4.2 MOSPF Example
MOSPF uses the flooding of membership reports within OSPF group-membership-
LSA messages to build an on-demand shortest path source specific multicast
tree. The shortest path calculation uses an RPF check from the sender network
towards the networks that have members of the host group. The RPF point is
determined by mapping the multicast source address to the source network in
the link state database. MOSPF therefore needs to be extended to enable a
source network to distribute an arbitrary mapping between source addresses
and source networks so that the RPF check can be undertaken towards the
source network that contains the FA and not the source network containing the
HA. One approach would be to include any non-local sender addresses in the
group-membership-LSA from the DR for the foreign subnet, which would cause
MOSPF routers to learn this association that would over-rule the default
mapping based on prefix matching. Clearly, this only works for member
senders, and non-local multicast senders need to wait for the flood to
complete before sending multicast packets into the domain to otherwise avoid
having packets fail the default RPF check. Alternatively, the DR could use
the FA/DR encapsulation of sect 6.3 whilst awaiting completion of the flood.
During hand-off, a controlled flood of the newRPF point is required within
the region encompassing the old DR, newDR and cross-over routers to Redirect
the RPF point for the non-local multicast source address. This can be
achieved by the newDR advertising the MN HoA in an updated group-membership-
LSA, which it floods into the domain. The group-membership-LSA will reach all
routers in the domain but will likely reach the cross-over router very
quickly. The oldDR continues to also distribute the MN HoA in its group-
membership-LSA during the hand-off and only when this is complete does it
discard IGMP membership state and update its group-membership-LSA to omit
this MN HoA. During the hand-off, the MOSPF routers can use either the old or
new DRs as RPF points. After the hand-off, the newDR will be the sole RPF
point but in all routers beyond the local mobility region, a mixture of old
and newDR RPFs will exist until the flood has completed. This is fine because
the RPF interface will be the same for the old and newDRs outside of the
local mobility region by definition. It may be necessary for a flag to be
added to the group-membership-LSA to indicate whether or not it should be
forwarded beyond the local mobility region. This is to enable the group-
membership-LSAs to be generated sufficiently fast for good hand-off
performance without impacting the signalling overhead on all the links in the
domain. It is presently assumed however that aggregation through the presence
of multiple non-local source addresses per group-membership-LSA, the extended
MIP hand-off period provided by make before break cellular technologies and
the use of dual RPF points during that hand-off should be sufficient to avoid
the excessive transfer of group-membership-LSAs over domain links.
6.4.3 DVMRP / PIM-DM
These protocols use a data flood followed by a receiver prune to efficiently
support dense multicast membership. Both protocols use an RPF check towards
the multicast source address to control the data flood but the lack of
membership signalling in advance of data flow potentially renders the RPF
redirection model inappropriate. DVMRP does however maintain its own
multicast routing tables by propagating prefix routes and so there is
potentially an opportunity for host specific routes for non-local senders to
be included in this route distribution at the cost of routing stability.
Therefore these protocols should instead use FA/DR encapsulation or the
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RPF Redirect Option until they are extended with membership signalling
phases, a development which is not considered to be likely.
6.4.4 RPF Redirect Option and FA Encapsulation
The use of these techniques from section 6.3 to bypass the RPF check also
enable the host to learn the DR address on the foreign subnet as well as the
non-local source address. These can then be used in source specific Joins
as the destination address for tree building, instead of the non-local
senders address that is already included in the PIM Join for example. Once
the source specific Join is received back at the newDR then the RPF header or
encapsulation can be dropped. These can then be re-applied on each hand-off
whilst the routing protocol messaging in the domain adjusts the source
specific tree and hence enables the impact of fast hand-off on the routing
protocol to be minimise. A receiver and its receiver DR should however use
the rate of such sender DR changes to decide whether it is appropriate to
inject source specific Joins into the domain because clearly if the routing
protocol has insufficient time to converge then the RPF header or
encapsulation should be permanently used.
6.4.5 Incremental Deployment
Clearly, it is possible that each domain as a whole can be upgraded to
support RPF redirection in the signalling plane as discussed in section 6.4.
It is not however practical to expect that all such domains in the Internet
will be upgraded at the same time and it is also not possible for a sender DR
to know whether all domains on the path between the sender and all receivers
have been so upgraded. Waiting until all domains upgrade before an Internet-
wide flag day is not practical and creates a chicken and egg problem in that
no-one has a motivation to upgrade until everyone else has. Therefore, this
draft recommends that Multicast Border Routers (MBR) be aware of whether or
not the next hop domain supports RPF redirection. If supported, then all is
well and the multicast packet can be natively injected into that domain.
However, if it is not supported then the MBR needs to apply one of the
encapsulation techniques of 6.1 through 6.3, with 6.3 being mandated as the
default mechanism for on-demand tree building protocols and RP Register
encapsulation for PIM domains. This however needs to be assessed as part of
the inter-domain multicast routing architecture (BGMP et al).
6.4.6 Topological Leaps
The limited propagation of the RPF Redirections rely on the fact that the MN
is taking incremental steps across the edge of the topology such that the
number of routers whose RPF checks need to be updated is always localised and
hence limited. However, a MN could undertake a hand-off that represents a
gigantic leap across the Internet topology (corporate to public network,
public cellular to home ADSL etc) and hence create a massive number of
routers who are not on the tree and an additional number of routers whose RPF
points are invalidated. There are a number of solutions to this, which should
be triggered by the MN and the access router. Firstly, a MN clearly
understands its movement through changes in the NAI and/or prefixes that are
advertised to it. The MN can then expect that any multicast traffic is likely
to be interrupted as the tree is rebuilt towards that new access router, and
specifically that MN originated multicast might be overly affected. Secondly,
the new access router can determine from the previous access router address
(via PFANE or similar mechanism) that a topological leap has occurred. The
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access router can then use, for MN originated traffic, either a unicast
tunnel to the HA / root node, or alternatively a multicast tunnel to the
group, until the source tree is built towards the senders DR. At this point,
the current DR, can commence native forwarding and RPF redirection.
6.4.7. CCoA v HoA Summary
It is clear that one of the aims of using the HoA as a source address was to
avoid the mobility dynamics, as the CCoA changes, from being exposed to the
source specific state in the multicast routing protocol. RPF Redirection
itself though also involves exposing the multicast routing to the mobility
dynamics by propagating the evolving RPF point. This is however much less
problematic than exposing the CCoA for the following reasons. This is because
the RPF changes only need to be propagated in the local area where the
movement results in changes to the required incoming interface. In the wider
Internet the existing incoming interface (HoA,G,<anyremoteDR) is still valid,
and hence forwarding will continue to succeed for the existing state. In
contrast, a CCoA change must be propagated throughout the Internet routing
system to update (CCoA1,G) to (CCoA2,G) which is clearly impractical.
This problem could be avoided in IPv6 by using universal interfaceIds (eg
EUI-64) only, rather than the full 128 bit address (prefix + EUI) for the
source specific multicast forwarding state, leading to the use of (EUI,G)
state. A MN that is then moving between subnets will have an unchanged EUI
but an evolving prefix, the latter though being masked from the multicast
forwarding state that is now valid Internet wide. One can also imagine using
prefix1 + universal interfaceID in the multicast state, and mask out sub-
prefix1 bits from the Internet multicast system, where prefix1 represents
all the networks through which the mobile can roam and still use this
multicast address, and sub-prefix 1 masks away from the multicast protocol
the bits that will change as a MN moves through the sub-networks under
prefix1. This requires the multicast routing protocol to distribute and
maintain a source mask as well as the source address in the routing state,
but this is clearly overly complex. Finally, note that at the cost of a loss
of resolution it is possible to use similar techniques in IPv4 by using a
source network specific tree, rather than source specific tree, defined by a
prefix2 that covers the networks under which the tree is valid and through
which a sender to that group is allowed to roam. The least significant bits
are masked out so that any CCoA allocated to the MN under that prefix2 will
still be valid in the global multicast state. The cost here though is that
the loss of resolution will be problematic to some multicast routing
protocols in the local area close to the movement of the sender and probably
makes this impractical without significant multicast protocol redesign. It is
also invalid in the SSM model where all the source bits define the channel.
In summary, CCoAs can be masked from the multicast routing protocol by
limiting such protocols to (*,G) state and shared trees. Existing deployed
protocols (DVMRP, PIM) however already build source trees using (S,G) state,
and SSM specifically mandates such state. Other protocols build source trees
on-demand using the RPF check and hence do not keep (S,G) state but this is
likely to change due to the SSM requirements. The partial solution is to use
a mask to limit tree building based on invariant source bits with IPv6
specifically supporting this via the universal interface ID. The only
complete solution however, is to migrate to using the HoA for the source
state, and to modify the multicast protocols to support an arbitrary
RPF point and RPF redirection.
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7. AAA Support for MIP Multicast
The Register encapsulation, FA/DR encapsulation and the RPF redirection
techniques do not need additional assistance from the AAA layer other than
controlling whether or not its MN can exploit foreign multicast and in what
roles (sender/receiver etc). However, the hybrid multicast technique of
section 6.1 may need the assistance of the AAA layer if it is necessary for
the FA to know in advance from the HA if this capability is supported. This
could be undertaken through MIP RREQ/RREP (BU) extensions between the HA to
the FA but could alternatively be included in the state exchanged between the
home and foreign AAA systems. The latter is particularly useful if it enables
the home AAA to then dynamically assign a HA to the MN that is able to
support the hybrid function.
8. IPv6 Considerations
The present proposal for foreign multicast in MIPv6 is to use the CCoA as the
source address and use multicast BUs via the HA to populate the CNs with the
binding between the senders CCoA and the HoA. The MN then sends multicast
packets using the CCoA as the source address but including the Home Address
Option (HAO). The CNs can then isolate the transport and higher layers from
the CCoA changes as a MN moves by swapping the CCoA with the HAO. In
addition, the CNs can undertake source specific joins for ASM or SSM by
referring to the binding in the binding cache and sending these joins to the
CCoA at the foreign subnet rather than to the HoA on the home subnet.
Whilst architecturally nice given its similarity with the unicast model of
route optimisation, there is a critical difference. In the unicast model, the
routing state in the Internet is already in place for reach CCoA and
therefore the routing fabric is not affected by the senders mobility. Only
the binding cache is exposed to the mobility. In the multicast case, the
senders movement leads to the need to create a new source specific multicast
tree for (newCCoA, G) for the existing population of receivers, in all
routers between those receivers and the mobile sender. This not only causes
synchronised tree building activity from that receiver population, but also
has to be undertaken in some reasonable fraction of the hand-off interval to
be at all useful. In cellular systems, this interval can be a small number of
seconds and it is therefore clear that CCoA based multicast as mention in the
MIPv6 design is also flawed.
The techniques in this draft are therefore still clearly necessary and
applicable, and in some cases enhanced by the IPv6 mechanisms, especially in
regard to the RPF Redirect option. However, it is equally clear that the
absence of MIPv6 FA CoAs or multicast protocol standards severely limits what
can be achieved in regard to MIP multicast for a while. However, this equally
provides a fresher starting point from which to developed MIP foreign
multicast systems which include RPF redirection.
9. Security Considerations
Securing MIP and multicast router message exchanges are obvious minimal
requirements that always need to be observed. More detailed analysis of the
problem space, and of the solutions mention in this draft amongst other
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candidate proposals, for supporting HoA originated foreign multicast, is
necessary before concrete statements can be made about possible new threats
and required security mechanisms. It is however clear that a security review
will need to be undertaken specifically with the RPF Redirect option and RPF
redirection in general. In addition, controls need to be placed on what nodes
can tunnel multicast data to nodes such as the root node and the HA
especially at multicast border routers. In addition, the multicast tunnelling
to receivers by the FA/DR may be problematic.
10. Notice Regarding Intellectual Property Rights
Flarion's submissions will conform with RFC 2026. Flarion may seek patent
protection on some or all of the technical information submitted by its
employees in connection with the IETF's standards process. If part(s) of a
submission by Flarion is (are) included in a standard and Flarion owns
patent(s) and/or pending patent application(s) that are essential to
implementation of such included part(s) in said standard, Flarion is prepared
to grant a license on fair, reasonable, reciprocal (license back) and non-
discriminatory terms on such included part(s).
11. References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9,
RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997
[MIPv4] C.E. Perkins, ``IP Mobility Support for IPv4," RFC3220, January 2002.
[MIPv6] D. Johnson, C. Perkins, ``Mobility Support in IPv6", Internet-Draft,
draft-ietf-mobileip-ipv6-18.txt (work in progress), 1 June 2002.
[IGMPv3] B. Cain et al, " Internet Group Management Protocol Version 3",
Internet-draft, draft-ietf-idmr-igmp-v3-05.txt, November 2000.
[MLDv2] R. Vida, "Multicast Listener Discovery Version 2 (MLDv2) for IPv6",
Internet-draft, draft-vida-mld-v2-03.txt, June 2002.
[PIM-SM] B. Fenner et al, "Protocol Independent Multicast - Sparse Mode",
Internet-draft, draft-ietf-pim-sm-v2-new-05.txt, 1 March 2002
[SSM] H. Holbrook, B. Cain, "Source-Specific Multicast for IP", Internet-
draft, draft-ietf-ssm-arch-00.txt, 21 November 2001.
[PIM-DM] A. Adams et al, "Protocol Independent Multicast - Dense Mode",
Internet-draft, draft-ietf-pim-dm-new-v2-01.txt, February 15, 2002.
[DVMRP] T. Pusateri, "Distance Vector Multicast Routing Protocol", Internet-
draft, draft-ietf-idmr-dvmrp-v3-10, August 2000.
[MOSPF] J. Moy, "Multicast Extensions to OSPF", RFC 1584, March 1994.
A.W. O'Neill Expires Dec 2002 [Page 20]
Author's Addresses
Alan O'Neill
Flarion Technologies
Phone: +1 908 947 7033
Email: oneill@flarion.com
| PAFTECH AB 2003-2026 | 2026-04-23 23:36:16 |