Routing Without Rumor: Securing the Internet’s Routing System

This article is based on a paper originally published as part of the Global Commission on the Stability of Cyberspace’s Cyberstability Paper Series, “New Conditions and Constellations in Cyber” on Dec. 9, 2021.

The Domain Name System has provided the fundamental service of mapping internet names to addresses from almost the earliest days of the internet’s history. Billions of internet-connected devices use DNS continuously to look up Internet Protocol addresses of the named resources they want to connect to — for instance, a website such as www.2-5.org Once a device has the resource’s address, it can then communicate with the resource using the internet’s routing system.

Just as ensuring that DNS is secure, stable and resilient is a priority for 2-5.org, so is making sure that the routing system has these characteristics. Indeed, DNS itself depends on the internet’s routing system for its communications, so routing security is vital to DNS security too.

To better understand how these challenges can be met, it’s helpful to step back and remember what the internet is: a loosely interconnected network of networks that interact with each other at a multitude of locations, often across regions or countries.

Packets of data are transmitted within and between those networks, which utilize a collection of technical standards and rules called the IP suite. Every device that connects to the internet is uniquely identified by its IP address, which can take the form of either a 32-bit IPv4 address or a 128-bit IPv6 address. Similarly, every network that connects to the internet has an Autonomous System Number, which is used by routing protocols to identify the network within the global routing system.

The primary job of the routing system is to let networks know the available paths through the internet to specific destinations. Today, the system largely relies on a decentralized and implicit trust model — a hallmark of the internet’s design. No centralized authority dictates how or where networks interconnect globally, or which networks are authorized to assert reachability for an internet destination. Instead, networks share knowledge with each other about the available paths from devices to destination: They route “by rumor.”

THE BORDER GATEWAY PROTOCOL

Under the Border Gateway Protocol, the internet’s de-facto inter-domain routing protocol, local routing policies decide where and how internet traffic flows, but each network independently applies its own policies on what actions it takes, if any, with data that connects through its network.

BGP has scaled well over the past three decades because 1) it operates in a distributed manner, 2) it has no central point of control (nor failure), and 3) each network acts autonomously. While networks may base their routing policies on an array of pricing, performance and security characteristics, ultimately BGP can use any available path to reach a destination. Often, the choice of route may depend upon personal decisions by network administrators, as well as informal assessments of technical and even individual reliability.

ROUTE HIJACKS AND ROUTE LEAKS

Two prominent types of operational and security incidents occur in the routing system today: route hijacks and route leaks. Route hijacks reroute internet traffic to an unintended destination, while route leaks propagate routing information to an unintended audience. Both types of incidents can be accidental as well as malicious.

Preventing route hijacks and route leaks requires considerable coordination in the internet community, a concept that fundamentally goes against the BGP’s design tenets of distributed action and autonomous operations. A key characteristic of BGP is that any network can potentially announce reachability for any IP addresses to the entire world. That means that any network can potentially have a detrimental effect on the global reachability of any internet destination.

RESOURCE PUBLIC KEY INFRASTRUCTURE

Fortunately, there is a solution already receiving considerable deployment momentum, the Resource Public Key Infrastructure. RPKI provides an internet number resource certification infrastructure, analogous to the traditional PKI for websites. RPKI enables number resource allocation authorities and networks to specify Route Origin Authorizations that are cryptographically verifiable. ROAs can then be used by relying parties to confirm the routing information shared with them is from the authorized origin.

RPKI is standards-based and appears to be gaining traction in improving BGP security. But it also brings new challenges.

Specifically, RPKI creates new external and third-party dependencies that, as adoption continues, ultimately replace the traditionally autonomous operation of the routing system with a more centralized model. If too tightly coupled to the routing system, these dependencies may impact the robustness and resilience of the internet itself. Also, because RPKI relies on DNS and DNS depends on the routing system, network operators need to be careful not to introduce tightly coupled circular dependencies.

Regional Internet Registries, the organizations responsible for top-level number resource allocation, can potentially have direct operational implications on the routing system. Unlike DNS, the global RPKI as deployed does not have a single root of trust. Instead, it has multiple trust anchors, one operated by each of the RIRs. RPKI therefore brings significant new security, stability and resiliency requirements to RIRs, updating their traditional role of simply allocating ASNs and IP addresses with new operational requirements for ensuring the availability, confidentiality, integrity, and stability of this number resource certification infrastructure.

As part of improving BGP security and encouraging adoption of RPKI, the routing community started the Mutually Agreed Norms for Routing Security initiative in 2014. Supported by the Internet Society, MANRS aims to reduce the most common routing system vulnerabilities by creating a culture of collective responsibility towards the security, stability and resiliency of the global routing system. MANRS is continuing to gain traction, guiding internet operators on what they can do to make the routing system more reliable.

CONCLUSION

Routing by rumor has served the internet well, and a decade ago it may have been ideal because it avoided systemic dependencies. However, the increasingly critical role of the internet and the evolving cyberthreat landscape require a better approach for protecting routing information and preventing route leaks and route hijacks. As network operators deploy RPKI with security, stability and resiliency, the billions of internet-connected devices that use DNS to look up IP addresses can then communicate with those resources through networks that not only share routing information with one another as they’ve traditionally done, but also do something more. They’ll make sure that the routing information they share and use is secure — and route without rumor.