Consistent routing policy?

Mon Sep 16 11:47:17 UTC 2019

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.