Destination Preference Attribute for BGP

Fri Aug 18 22:22:59 UTC 2023

On Fri, Aug 18, 2023 at 2:36 PM Mark Tinka <mark at tinka.africa> wrote:

> [...]
> To be fair, you are talking about an arbitrary value of years back, on
> boxes you don't name running code you won't mention.
>
> This really not saying much :-).
>

Hi Mark,

I know it's annoying that I won't mention specifics.
Unfortunately, the last time I mentioned $vendor-specific information on
NANOG, it was picked up by the press, and turned into a multimillion dollar
kerfuffle with me at the center of the cross-hairs:
https://www.google.com/search?q=petach+kablooie&sca_esv=558180114&nirf=petah+kablooie&filter=0&biw=1580&bih=1008&dpr=2

After that, I've learned it's best to not name specific very-big-name
vendors on NANOG posts.

What I *can* say is that this was one of the primary vendors in the
Internet backbone space, running mainstream code.
The only reason it didn't affect more networks was a function of the
particular cluster of signalling communities being applied to all inbound
prefixes, and how they interacted with the vendor's hash algorithm.

Corner cases, while valid, do not speak to the majority. If this was a
> major issue, there would have been more noise about it by now.
>

I prefer to look at it the other way; the reason you didn't hear more noise
about it, is that we stubbed our toes on it early, and had relatively fast,
direct access to the development engineers to get it fixed within two
days.  It's precisely *bcause* people trip over corner cases and get them
fixed that they don't end up causing more widespread pain across the rest
of the Internet.

> There has been quite some noise about lengthy AS_PATH updates that bring
> some routers down, which has usually been fixed with improved BGP code. But
> even those are not too common, if one considers a 365-day period.
>

Oh, absolutely.  Bugs in implementations that either crash the router or
reset the BGP session are much more immediately visible than "that's odd,
it's taking my routers longer to converge than it should".

How many networks actually track their convergence time in a time series
database, and look at unusual trends, and then diagnose why the convergence
time is increasing, versus how many networks just note an increasing number
of "hey, your network seems to be slowing down" and throw more hardware at
the problem, while grumbling about why their big expensive routers seem to
be less powerful than a *nix box running gated?

I suspect there's more of these type of "corner cases" out there than you
recognize.
It's just that most networks don't dig into routing performance issues
unless it actually breaks the router, or kills BGP adjacencies.

If you *are* one of the few networks that tracks your router's convergence
time over time, and identifies and resolves unexpected increases in
convergence time, then yes, you absolutely have standing to tell me to pipe
down and go back into my corner again.  ;D

> Mark.
>

Thanks!

Matt
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