Subject: Anycast Address becoming Multicast address ....

From: Keshava Ayanur <[email-masked]>
Date: Fri, 06 May 2005 18:48:32 +0530

Hi,

When the global unicast address with prefix 2 (ex: DADA::100/2) is given for
the interface, Mobile IPV6 anycast address corresponding to this should be
as below( RFC 2526).

 Format of Reserved Subnet Anycast Addresses:

   |              n bits            |    121-n bits  |   7 bits   |

  +---------------------------------+-----------.-------+------------ +

   |      subnet prefix         | 111..111111 | anycast ID |

  +---------------------------------+------------------+----------- -+

                                      |   interface identifier field  |

So MIP6 any cast address corresponding to this global unicast address
(DADA::100/2) will be 

FFFF:FFFF:FFFF:FFFF:FFFE as  the subnet prefix will 11 (prefix length is 2
only)

This  FFFF:FFFF:FFFF:FFFF:FFFE is a multicast address.

But as per RFC 3513 IPv6 Addressing Architecture,

 "Anycast addresses are allocated from the unicast address space, using any
of the defined unicast address formats"

            Can someone clarify this in-discrepancy?

Regards,

keshava

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---

From: Mark Andrews <[email-masked]>
Date: Sat, 07 May 2005 10:06:30 +1000

>    |              n bits            |    121-n bits  |   7 bits   |

	Well in 2373 the minimum prefix len was 3 for the above
	address.  Basically all the prefixes in 2373 has enough
	bits to distinguish them from a multicast address, i.e. the
	prefix contained atleast one "zero" bit.  They also contained
	enough infomation to distinguish it from a reserved address,
	i.e. one "one" bit.

	The simplest thing may be to say the minimum prefix length is 8.

	Mark
--
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: [email-masked]

---

From: Sachin <[email-masked]>
Date: Wed, 11 May 2005 03:07:39 -0700

Hi,

Following are two issues related to Anycast can some one plz clarify on
same

First as raised by Keshava that anycast address corresponding to unicast
global address becoming multicast addresses, RFC has not put any
specific condition for prefix length, so as per RFC 3513 for the
following unassigned global addresses with prefix length less then 8 the
corresponding mip6 anycast address will be multicast

   Unassigned                            1110           1/16

   Unassigned                            1111 0         1/32

   Unassigned                            1111 10        1/64

   Unassigned                            1111 110       1/128

   Unassigned                            1111 1110 0    1/512

"RFC 3513

Allocation                            Prefix         Fraction of

                                         (binary)       Address Space

   -----------------------------------   --------       -------------

   Unassigned (see Note 1 below)         0000 0000      1/256

   Unassigned                            0000 0001      1/256

   Reserved for NSAP Allocation          0000 001       1/128 [RFC1888]

   Unassigned                            0000 01        1/64

   Unassigned                            0000 1         1/32

   Unassigned                            0001           1/16

   Global Unicast                        001            1/8   [RFC2374]

   Unassigned                            010            1/8

   Unassigned                            011            1/8

   Unassigned                            100            1/8

   Unassigned                            101            1/8

   Unassigned                            110            1/8

   Unassigned                            1110           1/16

   Unassigned                            1111 0         1/32

   Unassigned                            1111 10        1/64

   Unassigned                            1111 110       1/128

   Unassigned                            1111 1110 0    1/512

   Link-Local Unicast Addresses          1111 1110 10   1/1024

   Site-Local Unicast Addresses          1111 1110 11   1/1024

   Multicast Addresses                   1111 1111      1/256

"

2 The other issue is that for different prefix anycast address formed
can be same for example 

ipv6 address DDDD::FDF0:0:0:2/76

ipv6 address DDDD::2/64      

ipv6 address DDDD::FD00:0:0:2/72

MIP6 Anycast address

DDDD::FDFF:FFFF:FFFF:FFFE

Mobile nodes from these three different subnet; will generate same mip6
anycast address. So their home agent discovery reply may not be from
correct home network 

Kindly comment on this

Regards

Sachin

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Keshava Ayanur
Sent: Friday, May 06, 2005 6:19 AM
To: [email-masked]; [email-masked]
Subject: [Mip6] Anycast Address becoming Multicast address ....

Hi,

When the global unicast address with prefix 2 (ex: DADA::100/2) is given
for the interface, Mobile IPV6 anycast address corresponding to this
should be as below( RFC 2526).

FFFF:FFFF:FFFF:FFFF:FFFE as  the subnet prefix will 11 (prefix length is
2 only)

 

 "Anycast addresses are allocated from the unicast address space, using
any of the defined unicast address formats"

 

Regards,

keshava