Newbies Question: Do I really need to sacrifice Prefix-aggregation to do BGP Load-sharing?

Tom Beecher beecher at
Thu Oct 20 12:59:11 UTC 2022

1. Prepending by itself isn’t bad. Prepending past the point that it is
effective in accomplishing anything is what you generally want to avoid.
Even then, it’s not nearly as big a deal as some make it out to be in most

2. De-aggregation has it’s uses and it’s place. Have a /20 , but announcing
all the component /24s, even though you aren’t doing anything different
with any of those? Bad practice. You’re just polluting the global table
size for no good reason.  However, perhaps you have a set of hosts in a
single /24 that you want to try and protect from a prefix hijack. Announce
the /20 and that singe /24. Not perfect protection , but provides some
cover, and isn’t that big a deal.

The answers to all of these questions are really : “It depends on what you
are trying to do.” There are generally accepted solutions to certain
problems, and there are plenty of dumb solutions that are the only thing
possible due to circumstances, so sometimes that’s what you have to do too.

Don’t worry about the pitchforks so much. :)

On Thu, Oct 20, 2022 at 08:15 Pirawat WATANAPONGSE via NANOG <
nanog at> wrote:

> Dear all,
> Before all else:
> thank you all for the lightning-fast responses (even taking the time zone
> advantage into account).
> I really, really, really appreciate all your recommendations.
> Virtually all of you recommend prepending as the first choice.
> I also get the feeling that you guys consider de-aggregation “distasteful”
> (at the least) but sometimes unavoidable.
> I have considered the prepending myself, but dare not implement it yet
> for the fear that BGP (Human) Community will burn me alive, witch-hunt
> style,
> because of the following reasons:
> 1. I can see from looking glass(es) that my upstreams already practice
> prepending (some paths) at their level (at least 3 more hops [x4]),
> supposedly to “balance” their bandwidth.
> 2. Should I start prepending mine, I might upset their balance, causing
> them to prepend more, thus starting a “prepend war”. [I imagine that x20+
> prepending starts out this way]
> The way I see it, prepending (or maybe even the whole BGP-Path thing) is a
> local-optimization problem: it’s only best for someone, not globally.
> And the Higher-Tiers (Lower Tier-Numbers) will always “engineer” me in the
> end.
> Worse yet, I might be out-voted by de-aggregation insider “cultists”
> anyway.
> Which forces me to proactively ask you guys questions about
> ROV-Overlapping and ROV “Hijack Gap” soon, in another posting with separate
> “Subject:”.
> Again, Thank you.
> Cheers,
> Pirawat.
> P.S.  [Off-Topic] Any comment on the “SCION” System?
> Any good (I will even take "academically")?
> [Reference:]
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