Re: Networks ignoring prepends?

[James Jun <james.jun () towardex com>]

On Wed, Jan 24, 2024 at 07:25:42AM -0800, William Herrin wrote:

[ snip ]

> or I chose my words poorly. What I did say, and stand behind, was that
> applying local prefs moves BGP's route selection off the _defaults_,
> and if Centurylink was routing to me based instead on the defaults
> they'd have made a _good_ route selection instead of a _bad_ one.

This cuts both ways Bill.  First, 3356 is making an intended route selection, their customer who interconnects directly 
into 3356 demands this.  That customer who connects into 3356 probably had no idea that you (AS11875) would someday 
decide to take IP transit from a downstream AS of them, and your situation was likely never in their minds of 
consideration in their network planning.

_You_ want better connectivity from 3356 to 11875 for the explicit benefit of 11875, which _you_ operate and control.  
That's good, so let's continue.


> I do care whether you're routing packets in a reasonable way. When you
> pick the 10-AS path over the 3-AS path because the 10-AS path arrives
> from a customer, the odds that you're routing those packets in a
> _good_ way are very low. I get that a lot of you do that. I'm telling
> you that when you do, you're doing a _bad_ job. If you think you're
> justified, well, it's your business. But don't doubt for a second that
> you've served your customers poorly.

Conversely at the same time, the below is also equally true:

You (AS11875) have an operational need for good connectivity into 3356 but, you made a poor purchasing decision by 
buying IP transit for 11875 from a provider who has 10-AS path into 3356 instead of <=3 AS path.  You've done a _bad_ 
job here in selecting an inferior pathway into 3356, and what you SHOULD have done is to select an IP transit provider 
who has an optimal AS-path into 3356 to meet your operational need of having good connectivity into 3356.


> And before you suggest that I'm not your customer, let me point out
> what should be obvious: if none of your paying customers were trying
> to reach my network, I wouldn't notice which direction you routed my
> packets, let alone care. It's not about serving me, it's about serving
> your paying customers. My packets are their packets, and when you send
> _their_ packets along the scenic route, you have done a bad job.

We can do this all day long.  You (AS11875) also have the responsibility to yourself and your end-users to select and 
award business to an IP transit provider and make every reasonable efforts to ensuer that 11875 has good connectivity 
into 3356 as your operational needs require.  You've abrogated that responsibility in your own AS and decided to spew 
non-sense over the most critical and important knob that is more important than AS_PATH (LOCAL_PREF) in BGP-4 that was 
developed since NSFNET days and are telling us that we're doing a poor job.  Your argument fails.

The internet works upon the principle of "best-effort."  What you're describing is the net effect of that 
"best-effort", and you, as the operator and controller of AS11875 which is involved in the path are just as culpable 
and responsible.  Moreover, you, by being the operator of an AS in the problematic path, have the wherewithal and 
commercial ability to fix it, without involving the rest of us.  The answer right is in front of you.

James