AS 701 local-pref answer.

Mike Leber mleber at he.net
Tue Dec 18 03:37:30 UTC 2001


It's probably not safe to assume every 701 peer peers with each other, or
that 701 peers with every peer at every location 701 has a peering
session, which means different peers could get different routes.

In any case, it's easily adjusted by 701 customers that have a preference
with the aforementioned communities.

Mike.

On Mon, 17 Dec 2001, David Barak wrote:

> 
> Hi,
> 
> I don't think AS 701 (or any of its peers) are
> particularly worried about different best-paths in
> different regions.  This is the old
> hot-potato/cold-potato discussion, which I don't see a
> need to re-hash.  
> 
> Let's pretend that Bob's bait & tackle shop (AS
> 30,000) is multihomed to AS 701 and AS 1.  Bob would
> probably want AS701 origin traffic to prefer his AS701
> link, and his AS1 Origin traffic to prefer his Genuity
> link.  No problem there - they both see a route 1
> AS-hop away.  The question only comes when Bob wants
> to have all other traffic prefer one link or the
> other.  
> 
> If he chose to prepend his AS to AS701, then he would
> run the risk of Genuity being the preferred path from
> AS701, and AS701 would not advertise a path.  This
> would be a useful situation if, for instance, the
> Genuity link was a DS3, and the 701 link was a T1.  If
> they were equal bandwidth links, and Bob was trying to
> do traffic-sharing, then that would not be a good
> solution. 
> 
> AS 701 does have mechanisa for customers to do this,
> and their support people are more than happy to assist
> customers with their routing needs.  
> 
> By the way, the gentleman who referred to "customers,
> peers, and upstreams" as useful loc-pref settings
> should remember that AS701 doesn't have upstreams.  :)
> 
> David Barak
> I speak for myself only.
> "Quis custodes ipsos custodiet?" - Juvenal
> 
> --- Mike Leber <mleber at he.net> wrote:
> > 
> > Not to be like Columbo... However, there's just one
> > last question
> > bothering me.  Well ok, more than one :)
> > 
> > If it's like mentzer at mentzer.org said and 701
> > doesn't deterministicly
> > prefer customer routes (customers and peer routes at
> > the same local pref)
> > wouldn't this mean that they wouldn't have
> > consistent route announcments
> > in various parts of their network?
> > 
> > If a customer doesn't set the community to boost the
> > local pref, and 701
> > truly by default sets customers and peers to 100,
> > then 701 would be
> > announcing varying numbers of routes to the same
> > peer at different
> > locations.
> > 
> > Do they expect consistent route annoucements from
> > their peers?
> > 
> > Many networks out there insist upon this as a
> > requirement when peering.
> > 
> > Mike.
> > 
> > On Sun, 16 Dec 2001, Mike Leber wrote:
> > 
> > > 
> > > Thank you for pointing that out.  I was being
> > dense and reading way too
> > > much into the statements:
> > > 
> > > smentzer at mentzer.org wrote:
> > > > All the responses I have gotten indicate that
> > UUnet does indeed set
> > > > local-pref on both customers and peers to 100
> > (or leave default in this
> > > > case).  Thanks for all the responses...
> > > 
> > > Especially when the 701 communities were already
> > provided by German
> > > Martinez.  *DOH*
> > > 
> > > In other words, 701 transit customers that
> > actually want to ensure their
> > > downstream customer routes are announced by 701
> > had better set the
> > > appropriate community so that local pref gets set
> > above 100.  By default
> > > this is not done.
> > > 
> > > Pardon me while I get some much needed rest.
> > > 
> > > Mike.
> > > 
> > > On Sun, 16 Dec 2001, David Barak wrote:
> > > 
> > > > Mike Leber wrote:
> > > > 
> > > > >If they set local pref for both peers and
> > customers
> > > > >to 100 how do they
> > > > >ensure that the customer transit routes are
> > > > >announced to peers?
> > > > 
> > > > >The reason I ask this is because if a customer 
> > > > >announces a customer of
> > > > >theirs to you that a peer also has as a
> > customer >you
> > > > will have equal
> > > > >length routes for the same destination AS. 
> > While
> > > > >there are many ways to
> > > > >deterministicly prefer customer routes, local
> > pref
> > > > >is the most common.
> > > > 
> > > > AS 701 always announces the best route, as their
> > > > routers know it.  Their average AS-path length
> > is
> > > > under 2, so it doesn't seem to be a problem.  If
> > a
> > > > customer of AS 701 wants to insure that his/her
> > route
> > > > is advertised in all cases, s/he could send a
> > > > community which AS701 edge devices could use to
> > > > manipulate local-preference upward.  [this was
> > covered
> > > > in a previous posting on this topic]  I leave it
> > to
> > > > your imagination whether peers would be
> > permitted to
> > > > do this.
> > > > 
> > > > -David Barak
> > > > I only speak for myself.
> > > > "Quis custodes ipsos custodiet?" - Juvenal
> > > > 
> > > >
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