RE: Policy Routing

["Martin, Christian" <cmartin () gnilink net>]

Jeff,

Does the router with the OC-12 have other eBGP sessions?  Also, is the
customer a BGP customer?  Everyone keeps talking about their feed, but I
haven't seen you mention BGP with the customer.  Anyway, if you can connect
the OC-12 and the customer to the same router, then outbound traffic
vectoring is quite easily accomplished with BGP alone.  Simply increase the
weight attribute of all routes from this OC-12 peering.  Or, set the LPREF
high on the ebgp session and a lower LPREF on all iBGP sessions.  Or, set
the LPREF the same throughout the AS and rely on administrative distance and
igp cost to force traffic out the OC-12.  

If you want return traffic to flow back across this link, then depreference
the route(s) upstream using communities (most NSPs support the provider
backup setting, usually <ASN>:70), which, assuming your upstreams are well
connected and exchanging routes, will redirect all or most of the traffic
across the OC-12.  Or, you can use the good old AS-PATH padding, which is a
little less deterministic, but won't bounce traffic around too much across
your upstreams mutual peering connections.  This is quite common among the
RBOCs, actually, because of regulation and anti-slamming and other silly
things.

A second note of caution:  Using route depreferencing vs AS-PATH padding may
cause certain peering connections between your upstreams to become quite
saturated, particularly at OC-12 speeds.  However, it will force all, or
under certain policies, nearly all of the return traffic to a set of NLRI
across the circuit you choose, as long as your upstreams are well connected
to one another, allow customer depreferencing through communities, and treat
peer routes as worse than customer routes, but better than customer backup
routes. 

regards,
 -chris

(speaking on my own behalf using my own views)

> -----Original Message-----
> From: John Fraizer [mailto:nanog () Overkill EnterZone Net]
> Sent: Sunday, August 26, 2001 3:58 AM
> To: Jeff Cates
> Cc: Travis Pugh; nanog () merit edu
> Subject: RE: Policy Routing
>
>
>
>
> If the OC-12 connection is via a well connected provider and it's that
> much less expensive than your other providers, and it's 
> seeing that little
> traffic, I would suggest a MUCH simpler alternative: Tune 
> your route-maps
> to pref more traffic towards that provider OVERALL.  That 
> way, you'll save
> money on ALL of your customers and not just this one special case. ;)
>
>
> ---
> John Fraizer
> EnterZone, Inc
>
>
> On Sat, 25 Aug 2001, Jeff Cates wrote:
>
> > For the record, this "cheap path" is an OC-12 to a
> > well connected Tier 1 provider that we got a
> > "sweatheart" deal on, and, it's only 2 percent
> > utilized.
> >
> > Again, I want to emphasize that I wholeheartedly agree
> > with those who have commented on the concept of full
> > disclosure in a scenario such as this. I'm just
> > looking for technical opinions on how this can be
> > accomplished most effectively.
> >
> > --Jeff
> >
> > --- Przemyslaw Karwasiecki <karwas () ifxcorp com> wrote:
> > > John,
> > >
> > > First: I agree with you at your main point 110% so
> > > my other
> > >        comment is strictly technical in nature.
> > >
> > > Second: Correct me if I am wrong, but I believe that
> > > if you send
> > >         to company X full view over EBGP there is no
> > > technical
> > >         reason to forward packets over different AS
> > > path.
> > >         After all, you are advertising reachability
> > > via NEXT_HOP,
> > >         which will be your border router.
> > >
> > > Before you flame me, please let me reiterate that I
> > > agree with you
> > > on the main point, that making a false/misleading
> > > AS_PATH advertisements
> > > is bad. But I am just curious if it would work
> > > provided that you are
> > > able to forward packets based on some 'coloring'
> > > scheme,
> > > so please consider my comment more as a question
> > > then questioning :-)
> > >
> > > Thanks,
> > >
> > > Przemek.
> > >
> > >
> > > -----Original Message-----
> > > From: owner-nanog () merit edu
> > > [mailto:owner-nanog () merit edu]On Behalf Of
> > > John Fraizer
> > > Sent: Sunday, August 26, 2001 12:57 AM
> > > To: Jeff Cates
> > > Cc: nanog () merit edu
> > > Subject: Re: Policy Routing
> > >
> > >
> > >
> > >
> > > Replying to my own post with a bit more. (Forgive
> > > me!)
> > >
> > > Rereading your post, one would believe that since
> > > "Company X" is a BGP
> > > customer of yours, you're going to be sending them a
> > > full view.  Unless
> > > there is a knob that I'm not familiar with, that
> > > means that you're going
> > > to be sending them the _BEST_ routes that you see in
> > > your core and not
> > > just those from "NSP A" to which you are proposing
> > > to policy-route all of
> > > "Customer X's" traffic.  If this is indeed the case,
> > > I would think that
> > > policy-routing the customers traffic destined for
> > > "prefix Y" via a
> > > path other than the path listed in the NLRI you're
> > > sending "Customer X" on
> > > their BGP feed is outright fraud.
> > >
> > > Again, this is in the absence of full disclosure and
> > > it is my (non
> > > esquire) opinion.
> > >
> > >
> > > ---
> > > John Fraizer
> > > EnterZone, Inc
> > >
> > >
> > > On Sun, 26 Aug 2001, John Fraizer wrote:
> > >
> > > > I would be very upset if I were "Company X" and I
> > > found out that you were
> > > > policy-routing my traffic to the "cheap"
> > > connection vs the best
> > > > connection.
> > > >
> > > > Is it just me or do others on the list believe
> > > that in the absence of full
> > > > disclosure this would be shady at best?
> > > >
> > > >
> > > > ---
> > > > John Fraizer
> > > > EnterZone, Inc
> > > >
> > > >
> > > > On Sat, 25 Aug 2001, Jeff Cates wrote:
> > > >
> > > > > Hello,
> > > > >
> > > > > I am a network engineer at a regional southeast
> > > USA
> > > > > NSP. I am looking for some recommendations
> > > concerning
> > > > > a scenario that has been presented to me.
> > > > >
> > > > > My company is attempting to obtain company X's
> > > > > Internet transit traffic, which will be  BGP-4
> > > peering
> > > > > over either a T-3 or OC-3. Due to financial
> > > reasons,
> > > > > my upper management has proposed that I route
> > > company
> > > > > X's Internet traffic via a specific NSP that we
> > > peer
> > > > > with, we'll call them NSP-A. Apparently, NSP-A
> > > has a
> > > > > substantially cheaper rate than our other
> > > upstrem
> > > > > providers and it is anticipated that this
> > > customer
> > > > > will be sending a full T3 or OC-3's worth of
> > > traffic
> > > > > to us.
> > > > >
> > > > > Redirecting inbound traffic to company X via
> > > NSP-A can
> > > > > be accomplished very easily through use of AS
> > > path
> > > > > prepending, however, coming up with a solution
> > > for
> > > > > egress traffic from company X to NSP-A, via our
> > > AS,
> > > > > has proven a bit more challenging :-).
> > > > >
> > > > > The only feasible solution that I've been able
> > > to come
> > > > > up with is to stick customer X directly on the
> > > router
> > > > > that peers with NSP-A and employ the use of
> > > policy
> > > > > routing, which would enable me to set the next
> > > hop for
> > > > > company X's traffic to the peering address on
> > > NSP-A.
> > > > > Our NSP-A peering router is a Cisco 12016,
> > > running IOS
> > > > > 12.0(16)S2 and it has 256MB of DRAM.
> > > > >
> > > > > Additionally, it is configured with NetFlow and
> > > dCEF
> > > > > switching.
> > > > >
> > > > > I've never employed policy routing in this type
> > > of
> > > > > environment and I am concerned about the
> > > overhead that
> > > > > it might place on the router or on the traffic
> > > > > traversing the interface.
> > > > >
> > > > > I've also thought about MPLS TE, however, our
> > > core
> > > > > backbone does not run MPLS and even if we did, I
> > > > > believe I would still have to policy route the
> > > traffic
> > > > > to NSP-A once the MPLS label was popped off the
> > > last
> > > > > router in the path in transit to the NSP-A
> > > peering
> > > > > router.
> > > > >
> > > > > Any ideas or comments would be greatly
> > > appreciated.
> > > > > Thanks in advance,
> > > > >
> > > > > Jeff
> > > > >
> > > > > catesjl9394 () yahoo com
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