About address allocating

[Bob Fink]

At 09:53 PM 5/18/2000 +0800, Haisang Wu wrote:
>hi, I have the following questions about address allocating:
>   I know SLA is /48, and interface ID should be 64 bits,
>does it mean that the smallest unit when allocating address is /48?
>In other words, if I allocate a /48 to a large university, could I
>allocate a /48 to four middle schools, thus each middle school gets
>an block less than /48, which is /50. Is this plan reasonable?

This is under discussion by the registries, and the outcome isn't clear 
yet, i.e., what to do in general for allocating public topology prefixes 
longer than /48 to smaller sites. Meanwhile, it is safe to say that your 
plan is ok if you consider your multiple middle schools one logical 
"individual organization", which is more likely to work for CERNET where 
you speak for the organizations from an Internet policy point of view, as 
opposed to a public ISP providing IPv6 service to multiple different 
customers (organizations).

Quoting from RFC2374:

>>3.5 Site-Level Aggregation Identifier
>>
>>    The SLA ID field is used by an individual organization to create its
>>    own local addressing hierarchy and to identify subnets.  This is
>>    analogous to subnets in IPv4 except that each organization has a much
>>    greater number of subnets.  The 16 bit SLA ID field support 65,535
>>    individual subnets.
>>
>>    Organizations may choose to either route their SLA ID "flat" (e.g.,
>>    not create any logical relationship between the SLA identifiers that
>>    results in larger routing tables), or to create a two or more level
>>    hierarchy (that results in smaller routing tables) in the SLA ID
>>    field.  The latter is shown as follows:
>>
>>
>>Hinden, et. al.             Standards Track                     [Page 6]
>>
>>RFC 2374           IPv6 Global Unicast Address Format          July 1998
>>
>>
>>    |  n  |   16-n     |              64 bits                |
>>    +-----+------------+-------------------------------------+
>>    |SLA1 |   Subnet   |            Interface ID             |
>>    +-----+------------+-------------------------------------+
>>
>>          | m  |16-n-m |              64 bits                |
>>          +----+-------+-------------------------------------+
>>          |SLA2|Subnet |            Interface ID             |
>>          +----+-------+-------------------------------------+
>>
>>    The approach chosen for structuring an SLA ID field is the
>>    responsibility of the individual organization.
>>
>>    The number of subnets supported in this address format should be
>>    sufficient for all but the largest of organizations.  Organizations
>>    which need additional subnets can arrange with the organization they
>>    are obtaining Internet service from to obtain additional site
>>    identifiers and use this to create additional subnets.


>   And, could those who get sTLA of /35 give me some detailed plan in
>address allocating? Thanks.
>   best

Take a look at ESnet's:

<http://esnet-v6r2.es.net/ipv6-addressing/>


Thanks,

Bob