Tag Archives: bgp

Another BGP blunder.but not THAT one

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Recently, there has been much talk about the Cloudflare BGP blunder and others. The Network Collective even did a video about such things. But did you know there was one involving the entire /12 of IPV6 space? Airtel AS9498 announced the entire IPv6 block 2400::/12 for a week and no-one noticed. Someone typed a /12 instead of a /127.

So why did no one notice? I think part of it is due to the low usage of v6 space.  Sure, all kinds of people claim stats on IPV6 usage.  They talk about X number of traffic is v6, etc. There is a difference between users and connections.  A connection may not actually represent unique users.

Secondly, people are used to IPV6 being buggy.  I know many ISPs who disabled v6 as part of their troubleshooting steps.

I know there will be several folks who jump all over me about IPV6 being the wave of the future and we all should be using it.  Yes, we should, but there is no huge hurry when it comes to business cases.

Noction: BGP in Large Networks

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Are you running a large scale BGP network? Need some tips and help on what to optimize and what your next steps to optimize your setup?

Using iBGP with loopback addresses
Making sure all routers know next hop and loopback addresses
Whether to use route reflectors rather than an iBGP full mesh
Where to originate prefixes
Where and how to filter announcements

Using BGP in large scale networks and how to get the most out of it. Paper by Noction

Remote Peering

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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.

https://www.globalpeeringforum.org/pastEvents/gpf14/presentations/Wed_2_MartinLevy_remote_peering_is_bad_for.pdf

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 routeviews.org 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.

BGP Monitoring RFC 7854

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https://tools.ietf.org/html/rfc7854

   This document defines the BGP Monitoring Protocol (BMP), which can be
   used to monitor BGP sessions.  BMP is intended to provide a
   convenient interface for obtaining route views.  Prior to the
   introduction of BMP, screen scraping was the most commonly used
   approach to obtaining such views.  The design goals are to keep BMP
   simple, useful, easily implemented, and minimally service affecting.
   BMP is not suitable for use as a routing protocol.

BGP Confederations

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In network routing, BGP confederation is a method to use Border Gateway Protocol (BGP) to subdivide a single autonomous system (AS) into multiple internal sub-AS’s, yet still advertise as a single AS to external peers. This is done to reduce the number of entries in the iBGP routing table.  If you are familiar with breaking OSPF domains up into areas, BGP confederations are not that much different, at least from a conceptual view.

And, much like OSPF areas, confederations were born when routers had less CPU and less ram than they do in today’s modern networks. MPLS has superseded the need for confederations in many cases. I have seen organizations, who have different policies and different admins break up their larger networks into confederations.  This allows each group to go their own directions with routing policies and such.

if you want to read the RFC:https://tools.ietf.org/html/rfc5065

The problem with peering from a logistics standpoint

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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.

Transit, peer, upstream. What do they all mean?

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As a service provider, you have a mountain of terms to deal with. As you dive into the realm of BGP, you will hear many terms in regards to peers.  Knowing their names AND your definition of them will serve you well.  I emphasized the and in the last sentence because many people have different definitions of what these terms means. This can be due to how long they have been dealing with networks, what they do with them, and other such things.  For example, many content providers use the term transit differently than an ISP.  So, let’s get on to it.

Transit or upstream
This is what you will hear most often.  A transit peer is someone who you go “through” in order to reach the internet.  You transit their network to reach other networks.  Many folks use the term “upstream provider” when talking about someone they buy their internet from.

Downstream
Someone who is “downstream” is someone  you are providing Internet to.  They are “transiting” your network to reach the Internet.  This is typically someone you are selling Internet to.

Peer
This is the term which probably needs the most clarification when communicating with others about how your BGP is setup.  A peer is most often used as a generic term, much like Soda (or pop depending on where you are from). For example someone could say:
“I have a peer setup with my upstream provider who is Cogent.” This is perfectly acceptable when used with the addition of “my upstream provider”.  Peers are often referred to as “neighbors” or “BGP neighbors”.

Local or Private Peer
So what is a local peer? A local peer is a network you are “peering” with and you are only exchanging routes which are their own or their downstream networks.  A local peer usually happens most often at an Internet Exchange (IX) but can happen in common points where networks meet. The most important thing that defines a local peer is you are not using them to reach IP space which is not being advertised form their ASN.   Your peering relationship is just between the two of you. This gets a little muddy when you are peering on an IX, but thats being picky.

I have trained myself to qualify what I mean by a peer when talking about them. I will often say a “transit peer” or a “local peer”. This helps to add a little bit of clarity to what you mean.

Why is this all important? For one, it helps with keeping everyone on the same page when talking about peering.  I had a case a few weeks ago where a Content provider and I wasted configuration time because our definition of transit was different.  Secondly, you want to be able to classify your peers so you can apply different filter rules to them. For example, with a downstream peer you only want to accept the IP space they have shown you which is their own.  That way you are not sending your own transit traffic over their network. This would be bad.  However, if you are accepting full routes from your transit provider, you want your filters to accept much more IP than a downstream provider. So if you have a team being able to be on the same page about peers will help when it comes to writing filters, and how your routers “treat” the peer in terms of access lists, route filters, etc.