Re: Xfinity on Campus

[Brian Turnbow via NANOG <nanog () lists nanog org>]

Hi Stephen

It really depends on the network you are advertising.
Say for example you are advertising a /24 or /48 that is  part of a
block being advertised directly  by 7922, or maybe the university's AS.
In this case even without announcing your netblock outside of 7922 they
will still be receiving the traffic via their announcement. so no
blackholing and traffic would still be coming in from the customers to you.
You can check this via looking glasses /route servers etc
Your logic would apply only to a unique netblock that is covered by another
announcement.

HTH
Brian



Brian Turnbow
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Il giorno mer 14 mag 2025 alle ore 17:09 Stephen Griffin via NANOG <
nanog () lists nanog org> ha scritto:

> So, I currently work for a university that offers Xfinity on Campus for our
> students. As part of that, we receive essentially peering.. with a twist...
> it is actually configured more like a normal customer.
>
> We're required to send 7922:999, which is essentially 7922's no-export.
> However, 7922:888 (7922+customers), seems like the better choice, while
> still respecting the goal of not providing transit.
>
> The former makes it such that 7922 doesn't advertise our prefixes to their
> BGP customers, which can lead to blackholes if their customer is
> default-free and their other provider(s) have an outage, or if the customer
> is doing link (but not provider) redundancy with BGP. It also means that
> billable traffic from xfinity customers to us is actually driven away from
> 7922, which would seem to not be in 7922's best interest (maybe folks no
> longer bill on usage?).
>
> no-export and its ilk just seems like the wrong choice in nearly every
> case, but I thought I would check myself with the assembled.
>
> Cheers,
> Stephen Griffin
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