AS 701 local-pref answer.

Daniel Golding dgolding at sockeye.com
Tue Dec 18 21:33:17 UTC 2001


As a clarification, MEDs would not help you out here in case of customer
prepending - unless you were ignoring AS-Path length. I'm not endorsing
that, as I've not heard of anyone trying it on a large scale.

- Daniel Golding

>
>
>
> Heh. Of course for AS's lacking usptreams, a more sensible sort of Local
> Preference hierarchy might be...
>
> Customer Prefered
> Customer
> Customer Backup
> Private Peers
> Congested Private Peers (perish the thought!)
> Good Public Peers (usually gigE exchange points)
> Bad Public Peers (Used to be FDDI, now ATM, i guess :)
>
> This is the usual ranking system used, with each category having both a
> local pref (and occasionally a range of LPs), and a destinctive community
> value.
>
> Although 701 has mechanisms for handling this (which work), the best
> approach for most folks who have both peers and customers, is to pref your
> customers, to ensure that their routes are always chosen in case of
> prepending. There are several reasons for this...
>
> 1 - Customers generally WANT traffic from directly connected
> networks. They
> also want to be able to prepend in order to balance traffic.
> 2 - Selecting a route through a peer, instead of a customer could
> adversely
> effect both your peering traffic balance, and your burstable billing model
> :)
>
> One way of accomplishing this sort of thing, if one were
> completely adverse
> to Local Preference, would be to use additive MEDs, and adding a large MED
> cost for peers, and a smaller one for customer routes, at point
> of ingress.
>
> - Daniel Golding
>
>
> > -----Original Message-----
> > From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu]On Behalf Of
> > David Barak
> > Sent: Monday, December 17, 2001 10:55 AM
> > To: Mike Leber
> > Cc: nanog at merit.edu; smentzer at mentzer.org; rekoil at semihuman.com;
> > gmartine at nic.gip.net
> > Subject: Re: AS 701 local-pref answer.
> >
> >
> >
> > 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
> > > > >
> > > > >
> > > __________________________________________________
> > > > > Do You Yahoo!?
> > > > > Check out Yahoo! Shopping and Yahoo! Auctions
> > > for all of
> > > > > your unique holiday gifts! Buy at
> > > http://shopping.yahoo.com
> > > > > or bid at http://auctions.yahoo.com
> > > > >
> > > >
> > > > +------------------- H U R R I C A N E - E L E C T
> > > R I C -------------------+
> > > > | Mike Leber             Direct Internet
> > > Connections     Voice 510 580 4100 |
> > > > | Hurricane Electric       Web Hosting  Colocation
> > >         Fax 510 580 4151 |
> > > > | mleber at he.net
> > >        http://www.he.net |
> > > >
> > >
> > +-----------------------------------------------------------------
> > ----------+
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > >
> > > +------------------- H U R R I C A N E - E L E C T R
> > > I C -------------------+
> > > | Mike Leber             Direct Internet Connections
> > >     Voice 510 580 4100 |
> > > | Hurricane Electric       Web Hosting  Colocation
> > >       Fax 510 580 4151 |
> > > | mleber at he.net
> > >      http://www.he.net |
> > >
> > +-----------------------------------------------------------------
> > ----------+
> > >
> >
> >
> > __________________________________________________
> > Do You Yahoo!?
> > Check out Yahoo! Shopping and Yahoo! Auctions for all of
> > your unique holiday gifts! Buy at http://shopping.yahoo.com
> > or bid at http://auctions.yahoo.com
> >
>




More information about the NANOG mailing list