One story that seems to have flown under the radar this week with the Net Neutrality discussion being so dominant was the little hiccup with BGP on Wednesday. According to sources, sources inside AS39523 were able to redirect traffic from some major sites like Facebook, Google, and Microsoft through their network. Since the ISP in question is located inside Russia, there’s been quite a lot of conversation about the purpose of this misconfiguration. Is it simply an accident? Or is it a nefarious plot? Regardless of the intent, the fact that we live in 2017 and can cause massive portions of Internet traffic to be rerouted has many people worried.
Routing by Suggestion
BGP is the foundation of the modern Internet. It’s how routes are exchanged between every autonomous system (AS) and how traffic destined for your favorite cloud service or cat picture hosting provider gets to where it’s supposed to be going. BGP is the glue that makes the Internet work.
But BGP, for all of the greatness that it provides, is still very fallible. It’s prone to misconfiguration. Look no further than the Level 3 outage last month. Or the outage that Google caused in Japan in August. And those are just the top searches from Google. There have been a myriad of problems over the course of the past couple of decades. Some are benign. Some are more malicious. And in almost every case they were preventable.
BGP runs on the idea that people configuring it know what they’re doing. Much like RIP, the suggestion of a better route is enough to make BGP change the way that traffic flows between systems. You don’t have to be a evil mad genius to see this in action. Anyone that’s ever made a typo in their BGP border router configuration will tell you that if you make your system look like an attractive candidate for being a transit network, BGP is more than happy to pump a tidal wave of traffic through your network without regard for the consequences.
But why does it do that? Why does BGP act so stupid sometimes in comparison to OSPF and EIGRP? Well, take a look at the BGP path selection mechanism. CCIEs can probably recite this by heart. Things like Local Preference, Weight, and AS_PATH govern how BGP will install routes and change transit paths. Notice that these are all set by the user. There are not automatic conditions outside of the route’s origin. Unlike OSPF and EIGRP, there is no consideration for bandwidth or link delay. Why?
Well, the old Internet wasn’t incredibly reliable from the WAN side. You couldn’t guarantee that the path to the next AS was the “best” path. It may be an old serial link. It could have a lot of delay in the transit path. It could also be the only method of getting your traffic to the Internet. Rather than letting the routing protocol make arbitrary decisions about link quality the designers of BGP left it up to the person making the configuration. You can configure BGP to do whatever you want. And it will do what you tell it to do. And if you’ve ever taken the CCIE lab you know that you can make BGP do some very interesting things when you’re faced with a challenge.
BGP assumes a minimum level of competency to use correctly. The protocol doesn’t have any built in checks to avoid doing stupid things outside of the basics of not installing incorrect routes in the routing table. If you suddenly start announcing someone else’s AS with better metrics then the global BGP network is going to think you’re the better version of that AS and swing traffic your way. That may not be what you want. Given that most BGP outages or configurations of this type only last a couple of hours until the mistake is discovered, it’s safe to say that fat fingers cause big BGP problems.
Buttoning Down BGP
How do we fix this? Well, aside from making sure that anyone touching BGP knows exactly what they’re doing? Not much. Some Regional Internet Registrars (RIRs) require you to preconfigure new prefixes with them before they can be brought online. As mentioned in this Reddit thread, RIPE is pretty good about that. But some ISPs, especially ones in the US that work with ARIN, are less strict about that. And in some cases, they don’t even bring the pre-loaded prefixes online at the correct time. That can cause headaches when trying to figure out why your networks aren’t being announced even though your config is right.
Another person pointed out the Mutually Agreed Norms for Routing Security (MANRS). These look like some very good common sense things that we need to be doing to ensure that routing protocols are secure from hijacks and other issues. But, MANRS is still a manual setup that relies on the people implementing it to know what they’re doing.
Lastly, another option would be the Resource Public Key Infrastructure (RPKI) service that’s offered by ARIN. This services allows people that own IP Address space to specify which autonomous systems can originate their prefixes. In theory, this is an awesome idea that gives a lot of weight to trusting that only specific ASes are allowed to announce prefixes. In practice, it requires the use of PKI cryptographic infrastructure on your edge routers. And anyone that’s ever configured PKI on even simple devices knows how big of a pain that can be. Mixing PKI and BGP may be enough to drive people back to sniffing glue.
BGP works. It’s relatively simple and gets the job done. But it is far too trusting. It assumes that the people running the Internet are nerdy pioneers embarking on a journey of discovery and knowledge sharing. It doesn’t believe for one minute that bad people could be trying to do things to hijack traffic. Or, better still, that some operator fresh from getting his CCNP isn’t going to reroute Facebook traffic through a Cisco 2524 router in Iowa. BGP needs to get better. Or we need to make some changes to ensure that even if BGP still believes that the Internet is a utopia someone is behind it to ensure those rose colored glasses don’t cause it to walk into a bus.
“BGP runs on the idea that people configuring it know what they’re doing.” That’s always been the problem with most of networking, except with BGP the mistakes that we all make can become very public, visible, and likely cause issues for others outside of our sphere of influence. 20 years ago when I learned BGP I used to muse that you weren’t a real network engineer until you’d leaked the global table to an upstream – who hopefully has at LEAST prefix limits on your peering. BGP has always been the easiest protocol to learn, but also the easiest to screw up. After this long running ISPs and large scale multi-homed networks, I can say with certainty that the issue is not only with BGP being easy to screw up, it’s that it “just works” and is relatively uncommon from the perspective of getting access to really do anything with it. It gets set up by someone green and then not touched until they need to change something, which they probably don’t really understand to do. Since it’s built on the handshake model, this often results in major blunders. My cynical side says that most of the lack of configuration resulting in large scale fumbles like this one is pure laziness. People don’t want to take the time to learn how to do it right when they can “make it work” by doing very little.
Pingback: Link Propagation 101 - Packet Pushers -
Great blog, interesting information.
Pingback: Do We Really Need a New BGP? – rule 11 reader
Pingback: Do We Really Need a New BGP? | Domain Industry News