Internet Engineering Task Force P. Bhattacharya
INTERNET DRAFT B. Patel
C. Perkins
IBM Research
22 February 1996
Preference for Multicast Support with Mobile IP
draft-partha-mobileip-mcastpref-00.txt
Status of This Memo
This document is a submission to the Mobile-IP Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the mobile-ip@smallworks.com mailing list.
Distribution of this memo is unlimited.
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Abstract
This document specifies a new extension to the Registration Request
used by mobile nodes with the mobile-IP protocol. The new extension
allows the mobile node to select the particular IP multicasts which
the home agent or foreign agent should forward to the mobile node
when it attaches to the Internet at a care-of address not on its home
network.
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1. Introduction
Mobile-IP [1] allows mobile nodes to move from one point of
attachment within the Internet to another, and defines mechanisms
by which a home agent on the mobile node's home network can send
datagrams to the mobile node. Since the mobile node's IP address
makes it seem to other routers as if the mobile node is on the
same network as the home agent (i.e., as if the mobile node is on
its "home network"), datagrams from other networks destined to the
mobile node will be transmitted onto the mobile node's home network,
where they can be received by the home agent and encapsulated for
delivery to the mobile node's care-of address. The mobile node's
care-of address can be an address assigned to one of the mobile
node's network interfaces, or it can be an address advertised by a
mobility agent near the current whereabouts of the mobile node. Such
a mobility agent is called a foreign agent.
A mobile node on a foreign network may need to send and receive
multicast packets either directly from the foreign network or from
its home network via its home agent. Depending on the application,
a mobile node may wish to have any of the above options on a per
multicast address basis. While the Mobile-IP specification specifies
relevant details about the transmission and reception of multicast
datagrams from its home network, it does not specify how a mobile
node can choose these options in a foreign network.
This document specifies an extension to the mobile-IP Registration
Request message to allow the mobile node to specify its options in
sending and receiving multicast datagrams on a per multicast address
basis. The mobile node appends the new extension to the Registration
Request it sends at its current point of attachment.
2. Multicast Preference Extension
The Multicast Preference extension allows a mobile node to specify,
at the time it registers its current care-of address, send and
receive options for various multicast addresses. The Multicast
Preference extension may be included several times within a single
registration request, once for every multicast address.
DISCUSSION:
What other constraints should be considered?
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+--+--+-+-+-+-+-+-+-+-+-+
| Type | Length |C|P|A|XH|XF|RH|RF| rsvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+--+--+--+-+-+-+-+-+-+-+-+-+
| Multicast IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 41
Length 4 + (4 * number of Multicast IP addresses listed)
C If the 'C' ('Clean') flag is set, the mobility agent is
instructed to eliminate any retained specifications for
multicast datagrams which the mobile node had included
in any previous Multicast Preference extensions.
P If the 'P' ('Permanent') flag is set, the mobility
agent is instructed to keep the following multicast
datagrams specification active until the mobile node
registers again using the 'C' flag.
A If the 'A' ('Additional') flag is set, the mobility
agent is instructed to include this preference for
receiving multicasts along with other preferences
previously specified by the mobile node.
If 'A' flag is not set (0), the mobility agent is
instructed to delete all non-permanent preferences
previously specified by the mobile node before storing
this preference.
If 'P' flag is set, 'A' flag is ignored.
XH If the 'XH' ('Transmit at Home') flag is set, then the
mobile node wishes to transmit packets destined to the
address specified in the Multicast IP address field, in
the mobile node's home network.
XF If the 'XH' ('Transmit in Foreign') flag is set, then
the mobile node wishes to transmit packets destined
to the address specified in the Multicast IP address
field, in the mobile node's foreign network.
RH If the 'RH' ('Receive from Home') flag is set, then the
mobile node wishes to receive packets destined to the
address specified in the Multicast IP address field,
from the mobile node's home network.
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RF If the 'RL' ('Receive from Foreign') flag is set, then
the mobile node wishes to receive packets destined
to the address specified in the Multicast IP address
field, in the mobile node's foreign network.
rsvd 0
Multicast IP addresses Flags and options specified by this
Multicast Preference extension apply to the Multicast
IP addresses listed in this field.
All extensions to the mobile-IP registration request have a type
field and a length field, as shown above. The number of Multicast
IP addresses listed will determine the length of the Multicast
Preference Extension.
If the mobile node wishes to clear ALL of its Multicast Preferences,
it sends a Multicast Preference Extension with the 'C' bit set, and
zero Multicast IP addresses listed.
3. Home Agent Considerations
If the home agent cannot satisfy the request, it MUST reject the
Registration Request by issuing a Registration Reply using the newly
defined status code:
145 Multicast Preference Not Supported
When a mobile node is attached to its home network, a home agent
MUST not forward multicasts to the mobile node. When a mobile node
is away from home, the following actions MUST be taken by the home
agent.
- If the 'XH' flag is set, then the home agent should transmit the
packets received from the mobile node, on the local network.
- If the 'XF' flag is set, no special actions are required from the
home agent.
- If the 'RH' flag is set, the home agent MUST respond to the IGMP
membership queries [2, 3] by including the multicast address
in its reports. The home agent MAY optionally tunnel the IGMP
membership queries to the mobile host. Also, the home agent MUST
tunnel the multicast packets to the mobile host for the specified
multicast address.
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- If the 'RF' flag is set, no special actions are required from the
home agent.
When a mobile node includes the 'P' flag in the Multicast Preference
extension to a registration request, the home agent MUST keep
track of the requested Multicast Preference(s) for the mobile node
until the mobile node clears the information with a new Multicast
Preference extension containing the 'C' flag. In this way, the
mobile node may be relieved of the requirement to send in the same
list of Multicast Preference extensions every time it registers at a
new care-of address.
4. Foreign Agent Considerations
If the 'XH' flag is set, then the Foreign agent MUST tunnel packets
received from the mobile node to the home agent.
If the 'XF' flag is set, and the foreign agent receives an
IP-within-IP datagram from the mobile node, then the foreign agent
MUST decapsulate the datagram, and replace the source address in the
multicast datagram with the Care-of-Address and submit the datagram
for IP processing.
If both 'XH' and 'XF' flags are set, both actions above MUST be
performed.
If the 'RH' flag is set, then the foreign agent MUST process tunneled
datagrams in one of the following ways:
- Transmit the multicast datagram from the interface sharing a link
with the mobile node, with TTL set to 1.
- Encapsulate the multicast datagram within a unicast IP datagram
addressed to the mobile node's home address, and submit for IP
processing.
If the 'RF' flag is set, and the foreign agent is acting as the
default router for the mobile node, the foreign agent transmits
multicast datagrams with the specified multicast address to the
mobile node.
5. Mobile Node Considerations
If the mobile host is attached to its home network, no special action
is required by mobile host.
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If the mobile host is attached to a foreign network, and the
Registration Request with the appended Multicast Preference Extension
was accepted by its home agent (and, if applicable, the foreign
agent advertising the care-of address used in the Registration), the
following actions are required.
If 'XH' flag was set, the mobile host MUST encapsulate every
multicast datagram within an unicast IP datagram addressed to the
home agent.
If 'XF' flag was set, it MUST do one of the following:
- Encapsulate every multicast datagram within an unicast IP
datagram addressed to the foreign agent.
- Transmit every multicast datagram with source address set to the
care-of address.
DISCUSSION:
Is this a reasonable way to offload processing from the foreign
agent? Should the Preference Extension contain another
flag to distinguish the two modes of operation?
If 'RH' flag was set, the mobile host MUST decapsulate IP in IP
packets [5].
If 'RF' flag was set, the mobile host MUST respond to the IGMP
membership queries.
6. Related Work
This draft specification is related to a companion draft
specification for the Broadcast Preference Extension for
Mobile-IP [4]. Changes to one document should be considered for
their impact on the issues in the other document.
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References
[1] IPv4 Mobility Support. ietf-draft-mobileip-protocol-15.txt -
work in progress, February 1996.
[2] Steve Deering. Host Extensions for IP Multicasting. RFC 1112,
August 1989.
[3] W. Fenner. Internet Group Management Protocol, Version 2.
draft-ietf-idmr-igmp-v2-02.txt -- work in progress, February
1996.
[4] B. Patel and C. Perkins. Preference for Broadcast Datagram
Support with Mobile IP. draft-perkins-mobileip-bcastpref-00.txt
-- work in progress, February 1996.
[5] Charles Perkins. IP Encapsulation within IP.
draft-ietf-ip4inip4-01.txt -- work in progress, October 1995.
Authors' Addresses
Questions about this memo can also be directed to:
Partha Bhattacharya Baiju Patel
Room H3-D40 Room H3-D36
T. J. Watson Research Center T. J. Watson Research Center
IBM Corporation IBM Corporation
Hawthorne, NY 10532 Hawthorne, NY 10532
30 Saw Mill River Rd. 30 Saw Mill River Rd.
Work: +1-914-784-7981 Work: +1-914-784-6786
Fax: +1-914-784-6205 Fax: +1-914-784-6205
E-mail: partha@watson.ibm.com E-mail: baiju@watson.ibm.com
Charles Perkins
Room H3-D34
T. J. Watson Research Center
IBM Corporation
30 Saw Mill River Rd.
Hawthorne, NY 10532
Work: +1-914-784-7350
Fax: +1-914-784-6205
E-mail: perk@watson.ibm.com
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