| MULTIMOB Group | T C. Schmidt |
| Internet-Draft | HAW Hamburg |
| Intended status: Informational | M. Waehlisch |
| Expires: September 29, 2011 | link-lab & FU Berlin |
| M. Farooq | |
| HAW Hamburg | |
| March 28, 2011 |
Mobile Multicast Sender Support in PMIPv6 Domains with Base Multicast Deployment
draft-schmidt-multimob-pmipv6-base-source-00
Multicast communication can be enabled in Proxy Mobile IPv6 domains by deploying MLD Proxy functions at Mobile Access Gateways, and multicast routing functions at Local Mobility Anchors. This document describes the support of mobile multicast senders in Proxy Mobile IPv6 domains that is provided by this base deployment scenario. Mobile sources remain agnostic of multicast mobility operations.
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].
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Proxy Mobile IPv6 (PMIPv6) [RFC5213] extends Mobile IPv6 (MIPv6) [RFC3775] by network-based management functions that enable IP mobility for a host without requiring its participation in any mobility-related signaling. Additional network entities called the Local Mobility Anchor (LMA), and Mobile Access Gateways (MAGs), are responsible for managing IP mobility on behalf of the mobile node (MN). An MN connected to a PMIPv6 domain, which only operates according to the base specifications of [RFC5213], cannot participate in multicast communication, as MAGs will discard group packets.
Multicast support for mobile listeners can be enabled within a PMIPv6 domain by deploying MLD Proxy functions at Mobile Access Gateways, and multicast routing functions at Local Mobility Anchors [I-D.ietf-multimob-pmipv6-base-solution]. This base deployment option is the simplest way to PMIPv6 multicast extensions in the sense that it neither requires new protocol operations nor additional infrastructure entities. Standard software functions need to be activated on PMIPv6 entities, only, on the price of possibly non-optimal multicast routing.
This document describes the support of mobile multicast senders in Proxy Mobile IPv6 domains as it is provided by the base deployment scenario [I-D.ietf-multimob-pmipv6-base-solution]. Mobile Nodes in this setting remain agnostic of multicast mobility operations. This document discusses implications on multicast routing, but does not address specific optimizations and efficiency improvements of multicast routing for network-based mobility as discussed in [RFC5757].
This document uses the terminology as defined for the mobility protocols [RFC3775], [RFC5213] and [RFC5844], as well as the multicast edge related protocols [RFC3376], [RFC3810] and [RFC4605].
The reference scenario for multicast deployment in Proxy Mobile IPv6 domains is illustrated in Figure 1.
+-------------+
| Multicast |
| Listeners |
+-------------+
|
*** *** *** ***
* ** ** ** *
* *
* Fixed Internet *
* *
* ** ** ** *
*** *** *** ***
/ \
+----+ +----+
|LMA1| |LMA2| Multicast Anchor
+----+ +----+
LMAA1 | | LMAA2
| |
\\ //\\
\\ // \\
\\ // \\ Unicast Tunnel
\\ // \\
\\ // \\
\\ // \\
Proxy-CoA1 || || Proxy-CoA2
+----+ +----+
|MAG1| |MAG2| MLD Proxy
+----+ +----+
| | |
MN-HNP1 | | MN-HNP2 | MN-HNP3
MN1 MN2 MN3
Multicast Sender + Listener(s)
An MN in a PMIPv6 domain will decide on multicast data transmission completely independent of its current mobility conditions. It will send packets as initiated by applications, using its source address with Home Network Prefix (HNP) and a multicast destination addresses chosen by application needs. Multicast packets will arrive at the currently active MAG via one of its downstream local (wireless) links. A multicast unaware MAG would simply discard these packets in the absence of a multicast forwarding information base (MFIB).
An MN can successfully distribute multicast data in PMIPv6, if MLD proxy functions are deployed at the MAG as described in [I-D.ietf-multimob-pmipv6-base-solution]. In this set-up, the MLD proxy instance serving a mobile multicast source has configured its upstream interface at the tunnel towards MN's corresponding LMA. For each LMA, there will be a separate instance of an MLD proxy.
According to the specifications given in [RFC4605], multicast data arriving from a downstream interface of an MLD proxy will be forwarded to the upstream interface and to all but the incoming downstream interfaces with appropriate forwarding states for this group. Thus multicast streams originating from an MN will arrive at the corresponding LMA and directly at all mobile receivers co-located at the same MAG. Serving as the designated multicast router or an additional MLD proxy, the LMA forwards data to the fixed Internet, if forwarding states are maintained through multicast routing. If the LMA is acting as another MLD proxy, it will forward the multicast data to its upstream interface, and based upon the downstream interfaces' subscriptions accordingly.
In case of a handover, the MN (unaware of IP mobility) can continue to send multicast packets as soon as network connectivity is reconfigured. At this time, the MAG has determined the corresponding LMA, and IPv6 unicast address configuration with PMIPv6 bindings have been performed. Multicast packets arriving at the MAG are discarded until the MAG has completed the following steps.
Figure 2). In this way, multicast source mobility is transparently enabled in PMIPv6 domains that deploy the base scenario for multicast.
As soon as the MN's uplink is associated with the corresponding MLD proxy instance, multicast packets are forwarded again to the LMA and eventually to receivers within the PMIP domain (see the call flow in
MN1 MAG1 MN2 MAG2 LMA | | | | | | | Mcast Data | | | | |<---------------+ | | | | Mcast Data | | | | Join(G) +================================================>| +--------------> | | | | | Mcast Data | | | | |<---------------+ | | | | | | | | | < Movement of MN 2 to MAG2 & PMIP Binding Update > | | | | | | | | |--- Rtr Sol -->| | | | |<-- Rtr Adv ---| | | | | | | | | | < MLD Proxy Configuration > | | | | | | | | | MLD Query | | | | |<--------------+ | | | | Mcast Data | | | | +-------------->| | | | | | Mcast Data | | | | +===============>| | | | | | | | Mcast Data | | | | |<================================================+ | Mcast Data | | | | |<---------------+ | | | | | | | |
These multicast deployment considerations likewise apply for mobile nodes that operate with their IPv4 stack enabled in a PMIPv6 domain. PMIPv6 can provide IPv4 home address mobility support [RFC5844]. IPv4 multicast is handled by an IGMP proxy function at the MAG in an analogous way.
Following these deployment steps, multicast traffic distribution transparently inter-operates with PMIPv6. It is worth noting that a MN - while being attached to the same MAG as the mobile source, but associated with a different LMA, cannot receive multicast traffic on a shortest path. Instead, multicast streams flow up to the LMA of the mobile source, are transferred to the LMA of the mobile listener and tunneled downwards to the MAG again (see Appendix Appendix A for further considerations).
Incorporating multicast source mobility in PMIPv6 requires to deploy general multicast functions at PMIPv6 routers and to define their interaction with the PMIPv6 protocol in the following way.
A Mobile Node willing to send multicast data will proceed as if attached to the fixed Internet. No specific mobility or other multicast related functionalities are required at the MN.
A Mobile Access Gateway is required to have MLD proxy instances deployed corresponding to each LMA, taking the corresponding tunnel as its unique upstream link, cf., [I-D.ietf-multimob-pmipv6-base-solution]. On the arrival of a MN, the MAG decides on the mapping of downstream links to a proxy instance and the upstream link to the LMA based on the regular Binding Update List as maintained by PMIPv6 standard operations. When multicast data is received from the MN, the MAG MUST identify the corresponding proxy instance from the incoming interface and forwards multicast data upstream according to [RFC4605].
The MAG MAY apply special admission control to enable multicast data transition from a MN. It is advisable to take special care that MLD proxy implementations do not redistribute multicast data to downstream interfaces without appropriate subscriptions in place.
For any MN, the Local Mobility Anchor acts as the persistent Home Agent and at the same time as the default multicast upstream for the corresponding MAG. It will manage and maintain a multicast forwarding information base for all group traffic arriving from its mobile sources. It SHOULD participate in multicast routing functions that enable traffic redistribution to all adjacent LMAs within the PMIPv6 domain and thereby ensure a continuous receptivity while the source is in motion.
An MN in a PMIPv6 domain may use an IPv4 address transparently for communication as specified in [RFC5844]. For this purpose, LMAs can register IPv4-Proxy-CoAs in its Binding Caches and MAGs can provide IPv4 support in access networks. Correspondingly, multicast membership management will be performed by the MN using IGMP. For multicast support on the network side, an IGMP proxy function needs to be deployed at MAGs in exactly the same way as for IPv6. [RFC4605] defines IGMP proxy behaviour in full agreement with IPv6/MLD. Thus IPv4 support can be transparently provided following the obvious deployment analogy.
For a dual-stack IPv4/IPv6 access network, the MAG proxy instances SHOULD choose multicast signaling according to address configurations on the link, but MAY submit IGMP and MLD queries in parallel, if needed. It should further be noted that the infrastructure cannot identify two data streams as identical when distributed via an IPv4 and IPv6 multicast group. Thus duplicate data may be forwarded on a heterogeneous network layer.
A particular note is worth giving the scenario of [RFC5845] in which overlapping private address spaces of different operators can be hosted in a PMIP domain by using GRE encapsulation with key identification. This scenario implies that unicast communication in the MAG-LMA tunnel can be individually identified per MN by the GRE keys. This scenario still does not impose any special treatment of multicast communication for the following reasons.
Multicast streams from and to MNs arrive at a MAG on point-to-point links (identical to unicast). between the routers and independent of any individual MN. So the MAG-proxy and the LMA SHOULD NOT use GRE key identifiers, but plain GRE encapsulation in multicast communication (including MLD queries and reports). Multicast traffic sent upstream and downstream of MAG-to-LMA tunnels proceeds as router-to-router forwarding according to the multicast forwarding information base (MFIB) of the MAG or LMA and independent of MN's unicast addresses, while the MAG proxy instance re-distributes multicast data down the point-to-point links (interfaces) according to its own MFIB, independent of MN's IP addresses.
In the following efficiency-related issues are enumerated.
There may be deployment scenarios, where multicast services are available throughout the access network independent of the PMIPv6 infrastructure. Direct multicast access at MAGs may be supported through native multicast routing within a flat access network that includes a multicast router, via dedicated (tunnel or VPN) links between MAGs and designated multicast routers.
Multicast traffic distribution can be simplified in these scenarios. A single proxy instance at MAGs with up-link into the multicast cloud will serve as a first hop gateway into the multicast routing domain and avoid traffic duplication or detour routing. However, mobility of the multicast source in this scenario will require some multicast routing protocols to rebuild distribution trees. This can cause significant service disruptions or delays (see [RFC5757] for further details).
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an RFC.
This draft does not introduce additional messages or novel protocol operations. Consequently, no new threats are introduced by this document in addition to those identified as security concerns of [RFC3810], [RFC4605], [RFC5213], and [RFC5844].
However, particular attention should be paid to implications of combining multicast and mobility management at network entities. As this specification allows mobile nodes to initiate the creation of multicast forwarding states at MAGs and LMAs while changing attachments, threats of resource exhaustion at PMIP routers and access networks arrive from rapid state changes, as well as from high volume data streams routed into access networks of limited capacities. In addition to proper authorization checks of MNs, rate controls at replicators MAY be required to protect the agents and the downstream networks. In particular, MLD proxy implementations at MAGs SHOULD carefully procure for automatic multicast state extinction on the departure of MNs, as mobile multicast listeners in the PMIPv6 domain will not actively terminate group membership prior to departure.
The authors would like to thank (in alphabetical order) Jouni Korhonen and Stig Venaas for advice, help and reviews of the document. Funding by the German Federal Ministry of Education and Research within the G-LAB Initiative is gratefully acknowledged.
| [RFC5757] | Schmidt, T., Waehlisch, M. and G. Fairhurst, "Multicast Mobility in Mobile IP Version 6 (MIPv6): Problem Statement and Brief Survey", RFC 5757, February 2010. |
| [RFC5845] | Muhanna, A., Khalil, M., Gundavelli, S. and K. Leung, "Generic Routing Encapsulation (GRE) Key Option for Proxy Mobile IPv6", RFC 5845, June 2010. |
| [RFC2236] | Fenner, W.C., "Internet Group Management Protocol, Version 2", RFC 2236, November 1997. |
TODO