About the address allocation convention between ISPs

Hi Teng,

From my experience it is standard practice for the provider of the

Internet connectivity to provide the /30 network IP addresses for
connectivity between two networks.

There are exceptions such as when using unnumbered interfaces, peering
points that share a common subnet between multiple ISPs, and when two
networks flip a coin on private peering interconnects (where generally
neither side is the provider to the other) to determine who is going
to provide the interface IPs.


Dear Mr. Wayrynen,

Thank you very much for your reply. What do you mean by "unnumbered
interfaces"? Also could you please confirm my question that if the
customer's address block was not obtained from the provider, it is also a
convention that the provider will provider the /30 address for the
inter-domain link?

From the replys, it seems to me that there is no way to tell which

link is indeed the inter-domain link, if the two ASes are peers. But for
customer-providers, I can guess with confidence. Could I get these
information from the IPSes' or PoP's website, about who are their
customers/peers? And how exactly the addresses were assigned?