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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-----
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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