IP Allocations

I have a question about how much IP space to allocate for downstream
customers. I know that when we want to obtain IP space that we have to
go to ARIN with the proper justification forms to show that we have
effeciently utilized our assigned IP CIDR's and also to verify that they
have been SWIP'd, etc... We also offer transport, so I came up with a
basic "rule of thumb" to use as a guideline. Up until recently, this has
worked fine. Now I am uncertain of what I should do with a customer that
is requesting a /23 CIDR, yet they only have 256K bandwidth. Part of me
says give it to them and let thier customers deal with the service that
they will receive, but then I feel obligated to not support bad ISP
service. I guess that I am looking for an industry guideline as opposed
to the one that I am trying to use or if I should even care. I use the
following: 256K = /26, 512K = /25, full T1 = /24, etc..
Let me know what everyone thinks, is this fair or not, and should I

Hey Mark,

Your rules of thumb are a little bizarre. Check rfc2050 -- and yes,
you _should_ care :slight_smile:


You should go to ARIN's website and carefully read the policies and other
documents there. Your guideline is completely wrong since it does not take
into account the actual number of IP addresses in use by the customer on
correctly configured equipment. ARIN's policies are all based on the
number of IP addresses actually in use and reasonable projection of the
actual number of IP addresses expected to be in use in the near future.
For specific number and times, you should review the website at

APNIC's and RIPE's also have on-line tutorials that walk a ISP through the
policies and example of IP assiments to customers.