"portability" of IP Addresses

Pete Kruckenberg pete at inquo.net
Fri Jan 31 04:09:53 UTC 1997

On Thu, 30 Jan 1997, Alan Hannan wrote:

>   Can a provider forbid their customer from announcing allocated
>   networks to another provider?
>   Assume the following situation:
>   ------------------------------
>   ISP A gets customer C to sign an agreement for service.  ISP A
>   allocates network A.B.C.0/20 to customer C.  A.B.C.0/20 is a
>   subnet of CIDR block A.B.0.0/16, allocated to ISP A by our friends
>   at the InterNIC as a non-portable address space.
>   So, customer C goes to ISP B, and says, I'd like to buy service
>   from you, and announce network A.B.C.0/20 to you.

I would think that ISP A would be all for it, since as soon as ISP B
starts announcing the /20, all in-bound traffic will come through ISP B
and relieve some of ISP A's bandwidth. Since ISP A is announcing a /16,
the /20 announced by ISP B would take precedence, being a more specific

I would think that ISP A would not have much to stand on from a legal
 - your contract does not prevent you from buying service from another
   provider (I'm assuming this), and (I further assume) it does not
   prohibit you from letting another ISP announce those routes
 - as it stands now (and will until ARIN changes it), ISP A does not
   actually *own* an IP addresses, and there is at least one RFC that
   makes this pretty clear, as well as several InterNIC policies
 - neither you nor ISP B are prohibiting ISP A from fulfilling their
   obligations to you or the rest of your customers by announcing the
   /20 separately
 - the announcement of the /20 does not cost ISP A anything extra, nor
   does it increase any contractual requirements for ISP A

This is a pretty gray area, though, but I think you have a pretty good
chance to be able to contest what ISP A says. That probably won't make
them go out of their way for you in the future, though.

Pete Kruckenberg
pete at inquo.net

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