Advertising rented IPv4 prefix from a different ASN.

Fri Aug 5 13:57:16 UTC 2016

Hi Andrew,

It is possible, but I would do it....Here is how and why.
If they announce the larger CDIR you will need to keep them as one of you
ISP's or you risk losing traffic due to other's inbound policy filtering.
However, if they provide you a simple Letter of Authorization to announce
the smaller rented CDIR you can use this letter to show other networks
that you have the right to announce it and they can email/call to confirm.
By announcing the smaller CDIR to others you should see the bulk of the
traffic come in via the other backbones. You can "not reliably" multi-home
the IPs without keeping the institution as one of your backbone providers
(reason I wouldn't do it). You will always need a peering session with
them where you announce to them your CDIR or they static route that
traffic to you.

Thank You
Bob Evans
CTO

> Hello List,
>
> I work for a medium sized ISP.  We are entering an agreement to rent
> some IPv4 space from a local higher education institution.  Being a
> multi-homed ISP we would like to advertise the rented prefix from our
> ASN.  The prefix that will be advertised is a smaller subnet from the
> higher educations block; they will continue to advertise the larger
> prefix.
>
> What is the best way to accomplish this?  Is there any way of doing this
> without having to tunnel the traffic through the origin ASN?
>
> I feel if we just adverse the prefix it get put on a bogon list for
> prefix hijacking.  This space is rented long term but they are not
> interested in reassigning the space to us.  They also want to keep
> advertising their prefix as one contiguous block.
>
> I appreciate any insight and information.
> Thank you for your time,
> Andrew.
>