Re: Peering + Transit Circuits

["Patrick W. Gilmore" <patrick () ianai net>]

Assume you and I are at an IX and peer. Suppose I send you traffic for Comcast. I can do this, even if you do not send 
me prefixes for Comcast. It requires me to manually configure things, but I can do it.

Put another way, you said "We will trust everything coming in”. I am saying that perhaps you should not.

As Comcast is not one of your customers, you will have to send the packets out your transit provider. You do not get 
paid when I give you the packets, and you probably pay your transit provider to get to Comcast. So I have gotten 
something for free, and you are paying for it - i.e. stealing.

Normally a router gets a packet and sends it on its way without looking at the source. However, if you have a router at 
the IX which has _only_ peer routes and your routes, that solves the problem. If I send you a packet for Comcast, your 
peering router will drop it and send an ICMP Network Unreachable. No filters to manage, no RIRs to sync, nothing to 
code, etc.

There are evil ways around this if you do not configure your router properly (e.g. send you a prefix for Comcast with 
next-hop set to inside your network). But standard network hygiene will stop those.

And as has been stated, this doesn’t have anything to do with URPF either. (Not sure why Nick brought that up, he’s 
smart enough to know what URPF is and runs an exchange himself, so I think he just brain-farted. Happens to us all.)

Hope that made it more clear.

-- 
TTFN,
patrick

> On Aug 18, 2015, at 6:35 PM, Faisal Imtiaz <faisal () snappytelecom net> wrote:
>
> Let me start backwards... 
>
> To me 'peering' is sharing internal routes and downstream customer routes,and not external ones.
>    IP transit is all of the external routes including internal routes & downstream customer routes
>
>
> Having said that..... if one is control of what IP Prefixes get advertised to whom... how exactly someone (peers) 
> 'steal' transit ?
> (If one is not managing the filters well then yes it is possible, but that would be a configuration error ?)
>
>
> Maybe I am naive, to my Peering routes (relationships) are a subset of IP Transit Routes (relationships)
>
> Based on above belief...
>
> Then Item # 3, becomes the choice of the OP.... where one can make one of two starting assumptions... We will trust 
> everything coming in and change what we don't like... or We will not trust anything coming in, and change (accept) 
> what we like.
>
> Items # 1 & 2, would be a function of network design, technical requirements (maintenance window) etc etc.. easier to 
> deal with a distributed edge vs all in one when one has to bring anything down for any reason..
>
> I am open to learning and being corrected if any of the above is wrong !
>
>
> Faisal Imtiaz
> Snappy Internet & Telecom
>
> ----- Original Message -----
> > From: "Tim Durack" <tdurack () gmail com>
> > To: cisco-nsp () puck nether net, "nanog list" <nanog () nanog org>
> > Sent: Tuesday, August 18, 2015 8:29:31 AM
> > Subject: Peering + Transit Circuits
>
> > Question: What is the preferred practice for separating peering and transit
> > circuits?
> >
> > 1. Terminate peering and transit on separate routers.
> > 2. Terminate peering and transit circuits in separate VRFs.
> > 3. QoS/QPPB (
> > https://www.nanog.org/meetings/nanog42/presentations/DavidSmith-PeeringPolicyEnforcement.pdf
> > )
> > 4. Don't worry about peers stealing transit.
> > 5. What is peering?
> >
> > Your comments are appreciated.
> >
> > --
> > Tim:>