Remote Peering

Martin J. Levy from Cloudflare did a presentation about remote peering possibly being a bad thing. In this presentation, he brings up several valid points.

Some thoughts of my own.

Yes, remote peering is happening.  One thing touched upon is the layer3 vs layer2 traffic.  We at MidWest-IX only allow remote peering at a layer2 level unless it is groups like or other non-customer traffic situations.

Many providers are overselling their backbone and transit links.  This oversubscription means access to content networks in places that do not have an exchange or places that do have the content locally can suffer through no fault of the ISP or the content provider.  We have situations with content folks like Netflix who do not join for-profit IXes at the moment, keeping the content further away from customers.  These customers are reaching Netflix through the same transit connections many other providers are.  The can result in congested ports and poor quality for the customer.  The ISP is left trying to find creative ways to offload that traffic.  An Internet Exchange is ideal for these companies because cross-connect charges within data centers are on the rise.

When we first turned up MidWest-IX, now known as FD-IX, in Indianapolis we used a layer2 connection to Chicago to bring some of the most needed peers down to our members.  This connection allowed us to kick-start our IX.  We had one member, who after peering with their top talkers, actually saw an increase in bandwidth.  The data gained told the member that their upstream providers were having a bottleneck issue. They had suspected this for a while, but this confirmed it. Either the upstream provider had a congested link, or their peering ports were getting full.

As content makes it way closer remote peering becomes less and less of an issue.  There are many rural broadband companies just now getting layer2 transport back to carrier hotels. These links may stretch a hundred miles or more to reach the data center.  The rural broadband provider will probably never get a carrier hotel close to them.  As they grow, they might be able to afford to host caching boxes. The additional cost and pipe size to fill the caches is also a determining factor. The tradeoff of hosting and filling multiple cache boxes outweighs the latency of a layer2 circuit back to a carrier hotel.

I think remote peering is necessary to by-pass full links which give the ISP more control over their bandwidth.  In today’s race to cut corners to improve the bottom line having more control over your own network is a good thing. By doing a layer2 remote peer you might actually cut down on your latency, even if your upstream ISP is peered or has cache boxes.

The problem with peering from a logistics standpoint

Many ISPs run into this problem as part of their growing pains.  This scenario usually starts happening with their third or 4th peer.

Scenario.  ISP grows beyond the single connection they have.  This can be 10 meg, 100 meg, gig or whatever.  They start out looking for redundancy. The ISP brings in a second provider, usually at around the same bandwidth level.  This way the network has two pretty equal paths to go out.

A unique problem usually develops as the network grows to the point of peaking the capacity of both of these connections.  The ISP has to make a decision. Do they increase the capacity to just one provider? Most don’t have the budget to increase capacities to both providers. Now, if you increase one you are favoring one provider over another until the budget allows you to increase capacity on both. You are essentially in a state where you have to favor one provider in order to keep up capacity.  If you fail over to the smaller pipe things could be just as bad as being down.

This is where many ISPs learn the hard way that BGP is not load balancing. But what about padding, communities, local-pref, and all that jazz? We will get to that.  In the meantime, our ISP may have the opportunity to get to an Internet Exchange (IX) and offload things like streaming traffic.  Traffic returns to a little more balance because you essentially have a 3rd provider with the IX connection. But, they growing pains don’t stop there.

As ISP’s, especially WISPs, have more and more resources to deal with cutting down latency they start seeking out better-peered networks.  The next growing pain that becomes apparent is the networks with lots of high-end peers tend to charge more money.  For the ISP to buy bandwidth, they usually have to do it in smaller quantities from these types of providers. Buying this way introduces the probably of a mismatched pipe size again with a twist. The twist is the more, and better peers a network has the more traffic is going to want to travel to that peer. So, the more expensive peer, which you are probably buying less of, now wants to handle more of your traffic.

So, the network geeks will bring up things like padding, communities, local-pref, and all the tricks BGP has.  But, at the end of the day, BGP is not load balancing.  You can *influence* traffic, but BGP does not allow you to say “I want 100 megs of traffic here, and 500 megs here.”  Keep in mind BGP deals with traffic to and from IP blocks, not the traffic itself.

So, how does the ISP solve this? Knowing about your upstream peers is the first thing.  BGP looking glasses, peer reports such as those from Hurricane Electric, and general news help keep you on top of things.  Things such as new peering points, acquisitions, and new data centers can influence an ISPs traffic.  If your equipment supports things such as NetFlow, sflow, and other tools you can begin to build a picture of your traffic and what ASNs it is going to. This is your first major step. Get tools to know what ASNs the traffic is going to   You can then take this data, and look at how your own peers are connected with these ASNs.  You will start to see things like provider A is poorly peered with ASN 2906.

Once you know who your peers are and have a good feel on their peering then you can influence your traffic.  If you know you don’t want to send traffic destined for ASN 2906 in or out provider A you can then start to implement AS padding and all the tricks we mentioned before.  But, you need the greater picture before you can do that.

One last note. Peering is dynamic.  You have to keep on top of the ecosystem as a whole.

BGP communities and traffic engineering

BGP communities can be powerful, but an almost mystical thing.  If you aren’t familiar with communities start here at Wikipedia.  For the purpose of part one of this article, we will talk about communities and how they can be utilized for traffic coming into your network. Part two of this article will talk about applying what you have classified to your peers.

So let’s jump into it.  Let’s start with XYZ ISP. They have the following BGP peers:

-Peer one is Typhoon Electric.  XYZ ISP buys an internet connection from Typhoon.
-Peer two is Basement3. XYZ ISP also buy an internet connection from Basement3
-Peer three is Mauler Automotive. XYZ ISP sells internet to Mauler Automotive.
-Peer four is HopOffACloud web hosting.  XYZ ISP and HopOffACloud are in the data center and have determined they exchange enough traffic amongst their ASN’s to justify a dedicated connection between them.
-Peer five is the local Internet exchange (IX) in the data center.

So now that we know who our peers are, we need to assign some communities and classify who goes in what community.  The Thing to keep in mind here, is communities are something you come up with. There are common numbers people use for communities, but there is no rule on what you have to number your communities as. So before we proceed we will need to also know what our own ASN is.  For XYZ we will say they were assigned AS64512. For those of you who are familiar with BGP, you will see this is a private ASN.  I just used this to lessen any confusion.  If you are following along at home replace 65412 with your own ASN.

So we will create four communities .

64512:100 = transit
64512:200 = peers
64512:300 = customers
64512:400 = my routes

Where did we create these? For now on paper.

So let’s break down each of these and how they apply to XYZ network. If you need some help with the terminology see this previous post.
64512:100 – Transit
Transit will apply to Typhoon Electric and Basement3.  These are companies you are buying internet transit from.

64512:200 – Peers
Peers apply to HopOffACloud and the IX. These are folks you are just exchanging your own and your customer’s routes with.

64512:300 – Customers
This applies to Mauler Automotive.  This is a customer buying Internet from you. They transit your network to get to the Internet.

64512:200 – Local
This applies to your own prefixes.  These are routes within your own network or this particular ASN.

Our next step is to take the incoming traffic and classify into one of these communities. Once we have it classified we can do stuff with it.

If we wanted to classify the Typhoon Electric traffic we would do the following in Mikrotik land:

/routing filter
add action=passthrough chain=TYPHOON-IN prefix= prefix-length=0-32 set-bgp-communities=64512:100 comment="Tag incoming prefixes with :100"

This would go at the top of your filter chain for the Typhoon Electric peer.  This simply applies 64512:100 to the prefixes learned from Typhoon.

In Cisco Land our configuration would look like this:

route-map Typhoon-in permit 20  
match ip address 102  
set community 64512:100

The above Cisco configuration creates a route map, matches a pre-existing access list named 102, and applies community 64512:100 to prefixes learned.

For Juniper you can add the following command to an incoming peer in policy-options:

set community Typhoon-in members 64512:100

Similar to the others you are applying this community to a policy.

So what have we done so far, we have taken the received prefixes from Typhoon Electric and applied community 64512:100 to it.  This simply puts a classifier on all traffic from that peer. We could modify the above example to classify traffic from our other peers based upon what community we want them tagged as.

In our next segment we will learn what we can do with these communities.