I like the curling analogy. No perfect load balancing across the Internet.
You can advertise the supernet out of all carriers and also advertise
individual /24's out of the preferred carrier. BGP will use the longer
subnet mask first and fallback to the supernet. If you have a bunch of
non-contiguous allocations then obviously that's not an option, but if
you have something bigger than a /24 then you can do it.
I also would note that if Connection "A" goes down, connection "B", "C",
or "D" might need to carry all the load and you may not know which way
it will come in. You can test and see what happens in a planned outage,
and tweak your settings just so, but I don't think you can guarantee
that topology upstream from you didn't change at some point between your
testing and the eventual unplanned outage. If you need 4Gb, then you
might just need two 4Gb pipes to have meaningful redundancy. Depends
what you're willing to live with. There's a saying that "slow is better
than down", but IMO the phone blows up either which way so best to avoid
either "slow" or "down" conditions.
I'll also note that every time I've ordered a 1gig circuit they gave me
GigE optics. If you order anything bigger, even if it's 1.1Gig then
it'll be a 10Gig interface by necessity. An upgrade then is just a
phone call, whereas the upgrade from 1Gig is a scheduled outage to swap
interface cards.
On 11/12/2020 7:15 PM, Matt Hoppes wrote:
Right. Which is not ideal.
On Nov 12, 2020, at 7:11 PM, Ken Hohhof <af...@kwisp.com> wrote:
There are smarter people than me here on the topic of BGP, but I believe
load balancing via prepends is an inexact science. It's like the guy with
the broom in curling, you can influence but not dictate the outcome.
You'd probably have better control advertising each subnet via just one of
the upstream providers, but then you lose the advantage of redundant feeds.
-----Original Message-----
From: AF <af-boun...@af.afmug.com> On Behalf Of Matt Hoppes
Sent: Thursday, November 12, 2020 5:45 PM
To: af@af.afmug.com
Subject: [AFMUG] Multiple carriers
I have a situation where I can buy several 1 gigabit pipes from several top
tier carriers relatively inexpensively.
Or I can buy one fat pipe from one carrier.
Say I need 4 gigabits of bandwidth and have four 1 gigabit pipes from 4
carriers running BGP, is there a best way to load balance these? Just AS
pre-pend subsets on each carrier so certain subnets prefer one over another?
Or is there a better way?
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