Consistent routing policy?

Mon Sep 16 12:47:53 UTC 2019

Thanks, Mark.  So the discrepancy between what's being advertised (/21 vs
/22) shouldn't cause any issues?  That's the part I got a bit confused
about.  I don't see how it would, but I wanted to make sure.

Thanks,
Ben

On Mon, Sep 16, 2019 at 7:47 AM Mark Tinka <mark.tinka at seacom.mu> wrote:

>
>
> On 16/Sep/19 13:35, Ben Logan wrote:
> > Hello,
> >
> > In reviewing our BGP routing policies last week, I realized that we
> > are advertising our address space upstream in slightly different ways
> > to our two upstream providers.  For example, we might advertise a /21
> > to one provider and break that into two /22s when advertising it to
> > the other.  (The reason this was done was to help with traffic
> > engineering--we'd prepend one of the /22s to help balance the
> > traffic.  Prepending the entire /21 might have been too much.)
> >
> > I'm just wondering if that's acceptable practice, or if we should
> > advertise consistent prefixes between providers?
>
> While de-aggregating certainly puts pressure on the Internet, it's
> reasonably acceptable if done conservatively. What you are doing is
> acceptable, so it can be considered okay, particularly if your bandwidth
> purchases from your upstreams is not symmetric.
>
> Also, I recall prepending did have some material result as much as 10
> years ago. I'm not sure whether it is as effective in 2019, considering
> how well peering has grown globally. From my side, since about 2012,
> it's a feature we haven't utilized in any way or form, even if we do
> currently offer it to our customers via a BGP community.
>
> YMMV...
>
> Mark.
>

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