IP Hijacking

IP hijacking (sometimes referred to as BGP hijacking, prefix hijacking or route hijacking) is the illegitimate takeover of groups of IP addresses by corrupting Internet routing tables.

The Internet is a global network in enabling any connected host, identified by its unique IP address, to talk to any other, anywhere in the world. This is achieved by passing data from one router to another, repeatedly moving each packet closer to its destination, until it is safely delivered. To do this, each router must be regularly supplied with up-to-date routing tables. At the global level, individual IP addresses are grouped together into prefixes. These prefixes will be originated, or owned, by an autonomous system (AS) and the routing tables between ASes are maintained using the Border Gateway Protocol (BGP). A group of networks that operate under a single external routing policy is known as an autonomous system. For example Sprint, MCI and AT&T each are an AS. Each AS has its own unique AS identifier number. BGP is the standard routing protocol used to exchange information about IP routing between autonomous systems.

Each AS uses BGP to advertise prefixes that it can deliver traffic to. For example if the network prefix 192.0.2.0/24 is inside AS 64496, then that AS will advertise to its provider(s) and/or peer(s) that it can deliver any traffic destined for 192.0.2.0/24.

IP hijacking can occur on purpose or by accident in one of several ways:

• An AS announces that it originates a prefix that it does not actually originate.
• An AS announces a more specific prefix than what may be announced by the true originating AS.
• An AS announces that it can route traffic to the hijacked AS through a shorter route than is already available, regardless of whether or not the route actually exists.

Common to these ways is their disruption of the normal routing of the network: packets end up being forwarded towards the wrong part of the network and then either enter an endless loop (and discarded), or are found at the mercy of the offending AS.

Typically ISPs filter BGP traffic, allowing BGP advertisements from their downstream networks to contain only valid IP space. However, a history of hijacking incidents shows this is not always the case.

IP hijacking is sometimes used by malicious users to obtain IP addresses for use with spamming or a distributed denial-of-service (DDoS) attack.