Re: Xfinity on Campus

[Christopher Morrow via NANOG <nanog () lists nanog org>]

I'd guess that Stephen already checked the looking-glass at:
  ssh rviewsxr () route-server newyork ny ibone comcast net

and validated that the prefix(s) in question are marked no-export...
I suspect that a university also brings their own IP and ASN to the party, so
seeing which prefixes have which communities is also something Stephen's done
before asking the original question.

yea... we can't (unless we are also comcast-campus-customers) know the contract
particulars, but the question at the end seems reasonable.

I'd suspect the overall assumption in the relationship is that the
prefixes seen on
7922 from the neighbors are equality visible to all folks that default
to comcast's network?
perhaps this is a situation where: "access to the comcast eyeball set"
is the goal of the relationship
not 'access to ALL comcast customers' ?

-chris

On Wed, May 14, 2025 at 11:31 AM Brian Turnbow via NANOG
<nanog () lists nanog org> wrote:
> 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
> +39 02 6706800
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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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