Dual Homed BGP

Sat Jan 25 00:49:21 UTC 2020

lør. 25. jan. 2020 00.40 skrev Jon Lewis <jlewis at lewis.org>:

> On Fri, 24 Jan 2020, Baldur Norddahl wrote:
>
> > Full tables will not make much noticeable difference if you are not
> peering. However you want to make sure both
> > links get used. It can be a 90%/10% split but 100%/0% is bad because
> then you may discover that the alternate path
> > is actually broken the moment the primary fail. If you choose only
> default then you need to think about that.
> > If you join any peering exchanges, full tables will be mandatory. Some
> parties will export prefixes and then expect
> > a more specific prefix received from your transit to override a part of
> the space received via the peering.
>
> 90/10 will suck when the link carrying 90% of your traffic needs more pipe
> and you have a ton of unused capacity on the other one.  Full tables from
> both providers gives you more options to tune things (assuming outbound is
> your larger direction).  If you're an eyeball provider and most of your
> traffic is inbound, your outbound traffic routing decisions aren't quite
> as relevant.
>

If your goal is to maximize your capacity, you should run a default route
with equal cost multi path for perfect load balancing. Just beware that
there is effectively no redundancy when exceeding the capacity of a single
link.

Also consider the typical two transits each connected to a separate router,
each router handling a single circuit. I will wager that the majority of
such dual homed organisations have no idea that those two routers by
default will make different routing decisions. You get more control but you
also need the experience and talent to use it. For many it might be better
to have a solution that is understood.

> Have those suggesting "multihoming with two partial feeds and default
> routes" forgotten peering pissing matches, long lasting inter-network
> capacity issues, or that certain "tier 1" providers don't even
> have/provide a full v6 table?
>

The solution is to stay clear of tier 1 networks. Find a good local tier 3.
Whatever you are going to do, they will do better.

Regards

Baldur
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