Embedding the Rendezvous Point Address in an IPv6 Multicast Address RFC 3956

1
Embedding the Rendezvous Point Address in
an IPv6 Multicast Address (RFC 3956)

• Presented by
• Dac Le
• The University of Texas at Arlington
• CSE5346

2
Outline

• Abbreviations
• Introduction
• Solution
• Unicast-Prefix-based Address Format
• Modified Unicast-Prefix-based Address Format
• Embedding the Address of the RP in the Multicast
  Address
• PIM-SM Group-to-RP Mapping use the encode
• Technical Challenges
• Conclusion

3
Abbreviations

• PIM-SM Protocol Independent Multicast - Sparse
  Mode
• RP Rendezvous Point
• MSDP Multicast Source Discovery Protocol
• RIID RP Interface ID
• SSM Source-Specific Multicast
• DR Designated Router

4
Introduction

• Problem PIM-SM RPs have no way of communicating
  the information about multicast sources to other
  multicast domains as MSDP has not been specified
  for IPv6

5
Solution

• Unicast-Prefix-based Address Format( RFC3306 )

• flag 0 0 P T
• The first two bits are undefined, sent as zero
  and ignored on receipt.
• P 0 Not prefix based address
• P 1 Prefix based address
• If P 1 then T must be equal to 1
• reserved 0
• plen number of bits used from unicast prefix
• prefix bits not from prefix should be 0

6
Modified Unicast-Prefix-based Address
Format
11111111
flag
scope
reserved
RIID
Network prefix
Group ID
plen
8 bits 4 4 4 4
8 64 bits 32 bits

• flag 0 R P T
• R 1 Embedded-RP-address
• If R1 then P1 ? T1
• R 0 Not Embedded-RP-address
• P or T is not set to 1 unspecified behavior
• reserved 0
• plen number of bits used from prefix
• prefix bits not coming from prefix should be 0

7
Embedded RP addresses

• A multicast address must satisfy all of the
  following
• It must be a multicast address with flag set to
  0111
• "plen must not be 0 (i.e., not SSM), and
• "plen" must not be greater than 64.

8
Embedded RP addresses

• The address of the RP can be obtained from a
  multicast address satisfying the above criteria
  by taking the following two steps
• Copy the first "plen" bits of the "network
  prefix" to a zeroed 128-bit address structure,
  and
• replace the last 4 bits with the contents of
  "RIID".
• 20 bits 4 8 64
  32
• ---------------------------------------------
  ----------
• xtra bits RIID plen network prefix
  group ID
• ---------------------------------------------
  ----------
• \\
• gt copy plen
  bits of "network prefix"
• 
  -------------------------------------------------
  -------
• network
  pre 0000000000000000000000
• 
  -------------------------------------------------
  -------
• \\ gt
  copy RIID to the last 4 bits
• 
  -------------------------------------------------
  ---------
• network pre
  0000000000000000000 RIID
• Ex Multicast address FF7E08402001660300110
  41234abcd
• Address of RP 200166030011048/64

9
PIM-SM Group-to-RP Mapping

• The implementation will have to recognize the
  address format and derive and use the RP address
  by using the rules in the previous slides
• To avoid loops and inconsistencies, for addresses
  in the range FF70/12, the Embedded-RP mapping
  must be considered the longest possible match and
  higher priority than any other mechanism.
• This group-to-RP mapping mechanism must be
  supported by the RP, the DR adjacent to the
  senders, and any router on the path from any
  receiver to the RP

10
Overview of the Model

• The steps when a receiver wishes to join a group
• 1. A receiver finds out a group address by some
  means.
• 2. The receiver issues an Multicast Listener
  Discovery (MLD)
• Report, joining the group.
• 3. The receiver's DR will initiate the PIM-SM
  Join process towards the
• RP encoded in the multicast address.
• The steps when a sender wishes to send to a
  group
• 1. A sender finds out a group address by using an
  unspecified
• method.
• 2. The sender sends to the group.
• 3. The sender's DR will send the packets
  unicast-encapsulated in PIM-
• SM Register-messages to the RP address
  encoded in the multicast
• address.

11
Technical Challenges

• Nodes in a "foreign domain" may register to an
  RP, or send PIM Join to an RP. An outsider may
  use the RP to host his/hers own group.
• How to stop other people from using your RP for
  their sessions
• The addresses of RPs may expose to other kinds of
  attacks since they are encoded in the multicast
  addresses.

12
Conclusion

• This mechanism provides a simple solution for
• IPv6 interdomain Any Source Multicast.
• It can be used as a simple solution for IPv6
  intra-
• domain ASM with scoped multicast addresses.

13

• Questions?