Peering + Transit Circuits

Tue Aug 18 23:38:18 UTC 2015

On Aug 18, 2015, at 7:26 PM, Faisal Imtiaz <faisal at snappytelecom.net> wrote:
> 
> Thank you for the explanation..
> 
> However wouldn't a few other other attributes of the traffic show up .
>  e.g. you would have asymmetric traffic.. going out via us, but coming back via a totally another path ?

So? If I am a content provider, my transit has more out than in. If I can push some of that outbound traffic through you for free, I’ll get the inbound over my transit provider for free since inbound is so low.

> BTW, my comment "We will trust everything coming in" was in ref. to QOS tags.
> 
>>>>> 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.
> 
> In this scenario, the peering router is feeding routes to a Route Reflector ? 
> and not taking in full routes from the route reflector ?

The peering router has routes from the peers (since it peers directly with them), and routes from your internal network. Not sure where a router reflector comes into this. You can use one, or not, but it’s not relevant to which routes the peering router has.

>>>> But standard network hygiene will stop those.
> If there are any resources you could point to for these, I would be much obliged..

There are lots, but don’t have my references with me. There’s 10K+ people on this list, I’m sure someone else has a list they like. :)

-- 
TTFN,
patrick

> ----- Original Message -----
>> From: "Patrick W. Gilmore" <patrick at ianai.net>
>> To: "nanog list" <nanog at nanog.org>
>> Sent: Tuesday, August 18, 2015 7:12:23 PM
>> Subject: Re: Peering + Transit Circuits
> 
>> 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 at 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 at gmail.com>
>>>> To: cisco-nsp at puck.nether.net, "nanog list" <nanog at 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:>