valley free routing?

Blake Dunlap ikiris at
Wed Mar 5 22:37:47 UTC 2014

The AS I worked at back in the day did to a degree for willing parties.
Mostly small ISPs who all knew each other. We had at the time 3 regional
hub locations with interlinks, and peered settlement free with 2 - 3 ASs in
1 of the locations, and 1-2 ASs each in the other 2 locations, all of which
could opt to allow their prefixes to be heard by the others via communities.


On Wed, Mar 5, 2014 at 3:48 PM, Siegel, David <David.Siegel at>wrote:

> I can't think of any circumstances where the business "B" would be content
> transit traffic between A and C without some form of compensation.  That
> compensation may not involve payment for bits, however.  In theory, the
> compensation might be derived from something occurring at the application
> layer, but even in those cases that business relationship is probably not
> apparent from looking at prefix advertisements.  Business B is probably
> using b2b user agents, gre encap or some other method that makes both legs
> look like independent IP flows to network A and B.
> Interesting question, though.
> Dave
> -----Original Message-----
> From: William Herrin [mailto:bill at]
> Sent: Wednesday, March 05, 2014 2:08 PM
> To: Valdis Kletnieks
> Cc: nanog at
> Subject: Re: valley free routing?
> On Wed, Mar 5, 2014 at 4:00 PM,  <Valdis.Kletnieks at> wrote:
> > On Wed, 05 Mar 2014 15:23:55 -0500, William Herrin said:
> >> Can anyone tell me about a situation in which a route which was not
> >> valley free was not a result of a misconfiguration or a bad actor?
> >> For those who don't recall the terminology, a network path is valley
> >> free if it crosses exactly zero or one free peering links when
> >> traveling between the two endpoints.
> >
> > Assume 3 providers A B and C, where you have a single-homed customer
> > on A and a single-homed customer on C, and A and C don't peer.
> > Traffic may end up going thorugh an A-B peering and a B-C peering. And
> > whether A-B and B-C are a free peering or a paid transit is a business
> > deal, outside the scope of BGP, unless you want to abuse communities...
> >
> > Are A and/or C "bad actors" for not peering? Jury is still out on that
> one.
> Hi Valdis,
> It's that business deal I want to hear about. When A-B and B-C are free
> peering but the traffic goes A-B-C for some reason other than a
> misconfiguration or deliberate abuse. On or off list, I'd like to know
> about real-life use cases where folks do this on purpose.
> Regards,
> Bill Herrin
> --
> William D. Herrin ................ herrin at  bill at
> 3005 Crane Dr. ...................... Web: <> Falls
> Church, VA 22042-3004

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