neighbor discovery problem

[=?unknown-8bit?B?4KSG4KS24KWA4KS3IOCktuClgeCkleCljeCk?=]

In <E1KSswq-000AcK-Bz at dilbert.ticketswitch.com>, Pete French wrote:
>> The network is pretty simple,
>>
>> gateway :
>> em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>>         options=b<RXCSUM,TXCSUM,VLAN_MTU>
>>         inet6 fe80::207:e9ff:fe0e:dead%em0 prefixlen 64 scopeid 0x1 
>>         inet6 2a01:678:1:443:: prefixlen 64 
>>         inet6 2a01:678:100:: prefixlen 48 
>
>Hmmm, are machine numbers of all zeroes legal in IPv6 ? I would
>configure those as '2a01:678:1:443::1' and '2a01:678:100::1' if
>I were you. All zeroes as a machine number is certainly a no-no in
>IPv4, and I wouldn't use it in IPv6 either. I have no idea if it's
>actually a problem, but it gives me a bad feeling....

Yes, it is legal, and such address, with subnet prefix + all zeroes in the 
host identifier (or interface identifier) is known as subnet-router anycast 
address. For further information, check out RFC 4291, Section 2.6.1[1].

References:
[1] - http://tools.ietf.org/html/rfc4291#section-2.6.1

Ashish Shukla
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