The Internet is a highly unstable and non-reliable network which requires a strong routing protocol. There are about 493870 routes on the Internet and the number is increasing every day (CIDR Report). Border Gateway Protocol (BGP) is the exterior gateway routing protocol used for routing over the Internet worldwide. BGP exchanges routing information between autonomous systems over the Internet. An autonomous system (AS) can be defined as network or group of routers that implement the same routing policy (Halabi, 96). Routes are announced by the AS to its connecting AS and are thus advertised further.
Even though BGP is a stable protocol, various issues such as delayed convergence, instability, inbound and outbound policy changes continuously occur in the Internet (Mahajan, Wetherall, and Anderson 1). The issues can either occur due to misconfigurations, software bugs, and faulty hardware. Misconfiguration errors such as wrong prefix advertisement, wrong attributes, incorrect policy filters occur while advertising routes to the Internet. Such errors can lead to an outage of the Internet scaling from a short time span to even days.
In this paper, the causes of misconfigurations from the origin AS are discussed. The paper further explores the probable effects of such misconfigurations on the Internet routing table and connectivity, followed by a few real life incidents that caused the Internet to shut down. The paper concludes with discussing various methods that have been proposed earlier to prevent or at least localize the effects of such misconfigurations.
Overview of BGP
BGP is a special case of distance vector protocol called the path vector protocol used for routing between autonomous systems (Halabi, 102). Two types of BGP exists: (1) eBGP which acts as Exterior Gateway Protocol and is used for routing between two AS and (2) iBGP which acts as an Interior gateway Protocol and is used for routing within an AS (Halabi 126). BGP forms a peer connection between the two routers using a TCP session before exchanging routing information (Halabi 103,126). After the peer connection is established, the tow BGP routers exchanges routing information along with their attributes.
BGP attributes include parameters such as next hop address, local preference, MED values, and AS_Path. BGP routing policy uses the attributes for determining the best path to the destination (Halabi 168). AS_Path is one of the major attributes in the BGP decision process. AS_Path is a list of all the AS in path to reach the destination (Halabi 154). Whenever a route is advertised by an AS, it appends the AS number in the AS_Path field and then forwards the route (Halabi 154, 155). The right most AS number in the AS_Path is the origin AS, which generates the route in the BGP network. The less number of AS in the AS_Path, the better the route (Halabi 168).
The first factor that BGP checks in its decision process is whether the advertised route has a...